BDA Guide to Successful Brickwork, Third Edition

The BDA Guide toSUCCESSFUL BRICKWORK

Third Edition

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This Page is Intentionally Left Blank

The BDA Guide toSUCCESSFUL BRICKWORKThird Edition

Woodside House, Winkfield, Windsor, Berks

AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO

Butterworth-Heinemann is an imprint of Elsevier

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Butterworth-Heinemann is an imprint of ElsevierLinacre House, Jordan Hill, Oxford OX2 8DP30 Corporate Drive, Suite 400, Burlington, MA 01803

First published 1994Second edition 2000Reprinted 2001, 2002, 2003 (twice), 2004Third edition 2005

Copyright © 2005, The Brick Development Association. All rights reserved

The right of The Brick Development Association to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988

No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1T 4LP. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publisher

Permissions may be sought directly from Elsevier’s Science and Technology Rights Department in Oxford, UK: phone: (�44) (0) 1865 843830; fax: (�44) (0) 1865 853333; e-mail: [email protected]. You may also complete your request on-line via the Elsevier homepage (http://www.elsevier.com), by selecting ‘Customer Support’ and then ‘Obtaining Permissions’

British Library Cataloguing in Publication DataA catalogue record for this book is available from the British Library

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ISBN-13: 978-0-7506-6469-1ISBN-10: 0-7506-6469-X

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CONTENTS

Foreword viiTraining as a bricklayer viiiGlossary of terms xi

PREPARATION AND PROTECTION1.1 Reference and sample panels (B Carling) 11.2 Protection of newly built brickwork (G Pellatt) 31.3 Handling, storage and protection of

materials (M Rawson) 61.4 Estimating quantities of bricks and mortar

(M Hammett) 10

BRICKLAYING TECHNIQUES2.1 Setting-out facework – stretcher half-

bond (R Baldwin) 122.2 Gauge and storey rods (S Brown) 162.3 Line, level and plumb (M Procner) 202.4 Vertical perpends (M Lang) 282.5 Cutting bricks (D Pope) 312.6 Keeping brickwork clean (R Baldwin) 332.7 Finishing mortar joints (R Baldwin) 362.8 Pointing and repointing (R Baldwin) 392.9 Bricks of special shapes and sizes (R Baldwin) 44

GOOD PRACTICE3.1 Avoiding damage from extremes of

temperature (M Thorpe) 503.2 Blending facing bricks on site (R Baldwin) 533.3 External cavity walls (T Knight, R Baldwin) 563.4 Frog up or frog down? (G Foster) 663.5 Manholes and inspection chambers

(G Britton) 69

ACCESSORIES4.1 Mortars (C Wallace) 764.2 Ties in cavity walls (A Buckley) 824.3 Damp-proof courses (M Lang) 864.4 Insulated cavity walls (M Thorpe) 894.5 Vertical movement joints (M W Pearce) 944.6 Reinforced and post-tensioned brickwork

(D Pope, S Bell) 984.7 Brickwork on metal support systems (G Law) 106

SPECIFIC CONSTRUCTIONS5.1 Copings and cappings (M Procner) 1125.2 Cavity parapet walls (T Knight,

R Baldwin) 1195.3 Curved arches (K Lamb) 1245.4 Circular bull’s-eyes (R Daniel) 1295.5 Soldier arches (R Baldwin) 1335.6 Decorative brickwork (M Dacey) 1355.7 Curved brickwork (R Baldwin) 1435.8 Corbelling (B Wroe) 1475.9 Tumbling-in courses (G Wright) 1515.10 Fireplace openings, chimney breasts and

flues (G Pellatt) 1555.11 Chimney stacks for domestic fireplaces

(G Pellatt) 161

BACKGROUND TOPICS6.1 Efflorescence and lime staining

(T Knight) 1686.2 Frost attack and frost resistance

(T Knight) 1716.3 Sulfate attack on mortars (T Knight) 1736.4 Durability of brickwork (T Knight) 1766.5 Allowing for variations in brick sizes

(R Baldwin, T Knight) 1816.6 Appearance (T Knight, R Baldwin) 1866.7 Rain resistance of cavity walls

(C Powell) 1916.8 Reading construction drawings

(M W Pearce) 1976.9 Bricklaying tools and equipment

(M Procner) 2076.10 Brick manufacture (M Crosby) 2126.11 Blockwork inner leaves, walls and

partitions (R Daniel) 223

INNOVATION7.1 The individual unit 1 2287.2 Innovation in components 2307.3 Innovation in prefabrication systems 2327.4 Innovation in technique 2347.5 Innovation in construction systems 237

Index 239

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FOREWORD

The BDA Guide to SuccessfulBrickwork has been updated inits third edition to take accountof the European Standards forClay, Calcium Silicate, andConcrete Bricks. The original texthas been amended to takeaccount of the EuropeanStandards and new material oninnovations in bricks andbrickwork has been added.

The European Standard EN771-1 specifies the performancecharacteristics for clay masonryunits available throughout the EUEconomic Zone. This has changedthe technical performancecategorisation of clay brick butcurrent products manufactured,traded and sold in the UK willbroadly remain the same asexisting.

One of the visible signs of thenew European Standards will beCE-marking. The CE-mark is the

mark of conformity denoting thata product satisfies certainrequirements within EuropeanLaw – and by inference – in therelated European CEN Standards.CE-marking is not a legalrequirement of product sales oruse within the UK and Irelandalthough it is only a matter oftime before it becomes so. Thismeans that some clay brickproducts may exhibit the markwhile others will not immediatelydo so. Failure to carry a CE-markinfers no impediment on thetrading of any clay brick productsin the UK and Ireland. However,all brick products are, for theforeseeable future, able toconform to EN 771-1 with orwithout CE-marking being used.

The new British Standard forclay bricks is BS EN 771-1. Not allbricks and masonry productsproduced and used throughout

Europe are the same. Producttypes and construction practicesvary greatly. In the UK a NationalAnnex has been produced that ispublished towards the rear pagesof BS EN 771-1 as informativeguidance to specifiers and users.The annex is not a formal part ofthe Standard. The BritishStandards Institution has alsopublished BSI PAS 70:2003. Thispublication deals with specificissues of clay brick site-measureddimensions and tolerances andalso brickwork reference panelsfor appearance purposes that arenot dealt with in the main bodyof the Standard.

Throughout the third editionthe BS EN 771 reference is usedalthough there are some diagramswhich compare specificationsoriginally available under BS 3921with those now available underthe European Standard.

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TRAINING AS A BRICKLAYER

During the period of thepublication of AchievingSuccessful Brickwork the nationalapproach to the formalrecognition of craft competenceand associated practical andtheoretical examinationprocedures underwent a majorchange. Formerly, courses oftraining involved a fixed periodof study and practice based ontraditional apprenticeshipconcepts. The new approach,which removes the obligatoryfixed time element, assesses skillby ability to demonstratecompetence.

The new approach now totallyreplaces the former one andleads to a National VocationalQualification (NVQ). NVQs applyto a wide range of industrial andcommercial activities and are notexclusive to the constructionindustry. Eventually the intentionis that they will be extended toall vocational pursuits. An NVQ isa measure of competence of anindividual’s capability to carry outa range of work to performancecriteria which had been agreedby Industry. An NVQ is comprised

of a number of Units ofCompetence which can beaccumulated over any period oftime and in any sequence.

Such qualifications areaccessible to everyone. Traditionalbarriers such as age, duration oftraining, mode of training, whereand how skills had been acquired,are removed. The only constraintremaining is compliance withstatutory regulations and legalrequirements, e.g. some tasks canonly be performed by individualsabove a minimum age.

The Construction IndustryTraining Board (CITB) is the bodythat has been responsible fordefining the range of craftoccupations within theconstruction industry and forestablishing definitions andstandards of competence foreach occupation. It has alsoreviewed formerly existingqualification procedures andidentified appropriatearrangements for assessing workand awarding NVQs.

The CITB and the City andGuilds Institute of London – thebody that formerly awarded

recognition of craftpersonshipability – are now jointlyresponsible for assessment andawarding qualifications.

In theory an individual who isable to demonstrate competencein the skills and knowledgedefined as necessary for aparticular craft can seekassessment and becomequalified. However, in practice,most individuals will undertake aformal training programmewhich involves tuition andpractical work as well as ancillarystudies and this will be donethrough a college or othertraining establishment.

This book does not specificallyidentify the tasks covered in thevarious Units of Competencedefined and assessed under theNVQ scheme, but all theinformation and craft guidance iscomplementary to, and inaccordance with, the acceptedstandards adopted by theawarding bodies and therefore itmay be relied upon as up-to-dateand authoritative guidance onthe construction of modern brickmasonry.

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The Brick Development Association acknowledges the help and assistance provided by the followingpersons in the preparation of the written material featured in this publication.

Bob Baldwin PPGB

Consultant

Stuart Bell DipArch, RIBA, MICeramTechnical Director, Marshalls Clay

Products Ltd

George Britton ABL

Waltham Forest College

Stephen Brown MMGB

South Cheshire College

Bert Buckley MMGB

The Bournemouth & Poole College

Brian Carling MCIOB, MBIM, Dip.Ed.New College, Durham

Martin CrosbyRedland Bricks Ltd

Mark DaceyPontypridd Technical College

Ray Daniel PPGB

Cumbria College

Graham Foster MMGB, LCG

Stoke on Trent College

Terry Knight AA Dipl, ARIBA

Terry Knight Consultancy

Keith Lamb MMGB

Hull College of Further Education

Mick Lang ABL

Lewisham College, London

Graham Law C.Eng., M.I.Mech.E.,

M.I.Struct.E. Technical Director, ANCON

Stainless Steel Fixings Ltd

Mick Pearce JVP, Associate CIOB

Barnsley College, Yorkshire

Graham R. Pellatt MMGB

Highbury College, Portsmouth

David Pope MGB

Langley College, Bucks

Chris Powell MICeram, MIHT, ACIOB

Brick Development Association

Mick ProcnerOaklands College, St Albans

Malcolm Rawson MMGB

Leeds College

Malcolm Thorpe PPGB, MIOB, MBIM,

Dip.Ed.West Nottinghamshire College

Clive H. Wallace MMGB, LICW, LCG

Worcester College

Graham WrightLeicester Southfields College

Brian Wroe MGB

Wakefield College

Technical Editor Terry Knight.Design & origination of first edition Barrett Howe Group Ltd, Windsor, Berks.

Additional text and technical co-ordination of soft bound editionsMichael Hammett DipArch, ARIBA, Senior Architect, Brick Development Association

Michael Driver MA DipArch RIBA, Director and Senior Architect Brick Development Association

Advanced Pro Tools LtdAncon CCL LtdARC AggregatesBritish Cement AssociationRedland Bricks LtdBrick Development Association

Lead Sheet AssociationM. ProcnerBlakes Building ProfilesMarshalls Clay Products LtdButterley Brick LtdAlan Blanc DipArch, FRIBA

Ryarsh Brick LtdTerry Knight ConsultancyR. J. BaldwinD. PopeRed Bank Manufacturing Co Ltd

Photographs and illustrations used in this manual have been kindly supplied by the followingorganisations.

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BDA MEMBER COMPANIES

Baggeridge Brick plcBlockleys Brick LtdBovingdon BrickworksBroadmoor Brickworks LtdBulmer Brick & Tile Co LtdCarlton BrickCharnwood Forest Brick LtdColeford Brick & TileDunton Brothers

Freshfield LaneBrickworks LimitedHammill Brick LimitedHanson Building ProductsIbstock Brick LtdKingscourt BrickMichelmersh Brick & Tile Co LtdNormanton Brick Co LtdNorthcot Brick Limited

Ormonde Brick LtdPhoenix Brick Company LtdWm. C Reade of Aldeburgh LtdSelborne Tile & Brick LtdSwarland Brick Co LtdTyrone Brick LtdThe York Handmade Brick Co LtdWienerberger Ltd

The Brick Development Association Limited

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GLOSSARY OF TERMS

Actual size the size of anindividual brick or block asmeasured on site. It may vary fromthe work size within certainallowances for tolerance (see alsoco-ordinating size and work size)Air entrainer see plasticiserAngle grinder a powered handtool with a cutting/grinding discused for cutting bricks or blocksand also for cutting and chasingbrickwork or blockworkAngle support steel angle fixedto a steel or concrete frame,usually at each floor level, tosupport brickwork claddingAngles special shape bricks whichform non-right angled corners inwallsArch an assembly of bricks whichspans an opening in a wall. It isusually curved in form, but may bepractically flatArris any straight edge of a brickformed by the junction of its facesATR’s ‘as they rise’, a traditionalterm referring to stock bricks thatare drawn from the clamp or kilnand delivered to site unsorted forqualityAutoclave a pressure vessel usedin the manufacture of calciumsilicate bricks in which they aresubjected to super heated steam athigh pressureAxed arch an arch formed ofbricks cut to appropriate wedgeshape by the bricklayer (see also gauged arch)Band course a single course ofbricks forming a decorative contrastof brick colour, bonding or shapeBat a part brick, e.g. half-brick,three-quarter brick, used in

bonding brickwork at corners andends of wallsBatching the accurateproportioning of mortar materialsto produce a specified mortar mixBed the horizontal layer ofmortar on which a brick is laidBed face the face(s) of a brickusually laid in contact with amortar bedBed joint a horizontal joint inbrickworkBench saw a power-driven,circular saw mounted on a benchwhich has facilities for holding abrick or blockBenching floor of a manhole orinspection chamber formed todischarge into the drainage channelBevel (in full bevel square) a toolwith an adjustable steel blade formarking and checking angles whensetting out brickwork and layingbricksBolster a broad-bladed chisel ofhardened steel used for cuttingbrickBond (1) the arrangement ofbricks in brickwork, usuallyinterlocking, to distribute loadBond (2) the resistance todisplacement of individual bricks ina wall provided by the adhesivefunction of mortarBonding bricks part bricks, e.g.half- or three-quarter bricks, orspecially shaped units to facilitatebonding of brickwork at features,corners and ends of walls (see alsobat)Boulder clay a type of clayformed by glacial action. Itcontains mixed sizes of particlesfrom fine clays to boulders

Brick see calcium silicate, clay,common, concrete, engineering,extruded wire-cut, facing, fletton,perforated, pressed, semi-drypressed, soft-mud, stockBrick gauge a wooden tool toassist the accurate marking forcutting bricks to half- and three-quartersBrickearth silty clay or loam in ashallow deposit. Traditionally usedfor making clay bricksBritish Standards nationalstandards defining the sizes andproperties of materials and theirproper use in buildingBroken bond the use of partbricks to make good a bondingpattern where dimensions do notallow regularised bond patterns offull bricksBullnose special shaped brickwith a curved surface joining twoadjacent facesBull’s eye a circular opening inbrickwork formed with a completering of voussiorsCalcium silicate brick a brickmade from lime and sand (sandlime)and possibly with the addition ofcrushed flint (flintlime), autoclavedin steam under high pressureCant special shaped brick with asplayed surface joining twoadjacent facesCapping construction orcomponent at the top of a wall orparapet not providing a weatheredoverhang (see also coping)Cavity batten a timber batten,with lifting wires, sized totemporarily lie in the void of acavity wall to catch mortardroppings and assist their removal

*Terms printed in italics in the definitions are separately defined within this glossary.

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xii GLOSSARY OF TERMS

Cavity tray see DPC trayCavity wall wall of two leaveseffectively tied together with wallties with a space between them,usually at least 50 mm wideCellular block concrete blockwith large voids that do not passright through the unitCement see Portland cement andmasonry cementCentring temporary former tosupport underside of arch duringconstructionC&GIL City and Guilds Institute ofLondon. A national trainingauthorityChases recesses cut in walls toaccommodate service cables orpipescill see sillCITB Construction IndustryTraining Board. A national trainingauthorityClamp a large stack of moulded,dried clay bricks and crushed fuelwhich is set alight and burns to firethe bricksClay brick a brick made from clayformed in a moist condition, driedand fired in a kiln or clamp toproduce a hard semi-vitreous unitClosers bricks cut to expose ahalf header in the surface of a walland used as bonding bricksClub hammer heavy hammerused for striking bolster whencutting bricksCollar joint a continuous verticaljoint, parallel to the face of a wall,formed in walls one-brick or morethick when bricks are bonded inleaves of stretcher bondCommon brick a brick for generalpurpose applications whereappearance is not of significanceCompressive strength theaverage value of the crushingstrengths of a sample of brickstested to assess load bearingcapability

Concrete a mixture of sand,gravel, cement and water that setsand hardensConcrete brick a brick madefrom crushed rock aggregatebound with Portland cementCo-ordinating size size of aco-ordinating space allocated to abrick or block, including allowancefor mortar joints (see also work sizeand actual size)Coping construction, orcomponent, at the top of a wall orparapet that is weathered, groovedand overhangs the wall surfacebelow to throw water clear andprovide protection againstsaturation (see also capping)Corbel a feature, or course, orcourses of brick, projecting fromthe face of the wall, often forminga supportCorner block a wooden, orplastic, block to provide atemporary fixing at the ends of awall for a string line used to controllevelling of bricks or blocks whenbuildingCourse a row of bricks laid on amortar bed jointed in mortar,generally horizontallyCourse stuff a mixture of sandand lime to which cement andwater is added to make mortarCross joint vertical mortar joint atright angles to the face of the wall(sometimes incorrectly called a perp)Datum a fixed reference pointfrom which levels are set outDiaper decorative pattern ofdiagonal intersections or diamondshapes produced by contrastingcoloured bricks in a bondarrangementDogleg special shaped anglebrickDPC a layer or strip of imperviousmaterial placed in a joint of a wallchimney or similar construction toprevent the passage of water

DPC brick clay brick of specifiedmaximum water absorption ofwhich two courses may be built atthe base of a wall to prevent theupward movement of moistureDPC tray a wide DPC bedded inthe outer leaf, stepping in thecavity of a cavity wall, and builtinto the inner leaf. It diverts waterin the cavity through weep holes inthe outer leafDPM a layer or sheet ofimpervious material within orbelow a floor, or vertically within oron a wall, to prevent the passageof moistureDurability the ability of materialsto withstand the potentiallydestructive action of freezingconditions and chemical reactionswhen in a saturated stateEaves lower edge of a pitchedroof, or edge of a flat roofEfflorescence a white powderydeposit on the face of brickworkdue to the drying out of solublesalts washed from the bricksfollowing excessive wettingElevation a construction drawingshowing the view of a verticalsurface of a building or objectEngineering brick a type of claybrick traditionally used for civilengineering work for whichcharacteristics of great strengthand density are consideredbeneficial. They are defined bycompliance with minimumcompressive strength andmaximum water absorption values(stated in the British Standard forClay Bricks (BS 3921)Extrados the upper or outercurve of an arch (oppositeintrados)Extruded wire-cut bricks bricksformed by forcing stiff moist clay,under pressure, through a die andcutting the extruded shape intoindividual bricks with taut wires

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GLOSSARY OF TERMS xiii

Face work brickwork orblockwork built neatly and evenlywithout applied finishFacing brick a brick for use in theexposed surface of brickworkwhere consistent and acceptableappearance is requiredFireclay a type of clay containinga high proportion of silica,principally used for the manufactureof fire bricks because of itsresistance to high temperature. Alsoused for building bricks. Generallyproduces a buff colourFlashing waterproof sheetmaterial, usually lead, dressed toprevent entry of rain water at anabutment junction between roofand brickworkFletton bricks semi-dry pressedbricks made from lower Oxfordclay, originally made in Fletton,near Peterborough, andsubsequently widely usedthroughout the UKFlintlime brick see calciumsilicate brickFlue a duct, or pipe, that conveyssmoke from a fireplace or aheating appliance to the open airFooting a widening at the base ofbrickwork to form a bearing on thesupporting sub-soil. Traditionallya footing could be of brickworkbut in modern construction it isusually of in-situ concrete whenit is also referred to as a stripfoundationFoundation a sub-structure to bearon supporting sub-soil. May be piles,ground beams, a raft or footingsFrenchman a hand tool used toneatly cut off excess mortar whenforming certain mortar joint finishesFrog an indentation in one orboth bed faces of some types ofmoulded or pressed bricksFrost damage the destructiveaction of freezing water andthawing ice in saturated materials

Gable portion of a wall aboveeaves level that encloses the end ofa pitched roofGauge boxes boxes of specificvolumes to accurately measure theproportions of cement, lime andsand when preparing mortarGauge rod batten marked atintervals for vertical setting-out ofbrick coursesGauged arch an arch formed ofwedge-shaped bricks jointed withnon-tapered mortar jointsGault a clay associated with chalkdeposits of East Anglia. Generallybricks made with gault clay arecream or yellow in colour but theymay be light redGun template template shapedto set out angled alignment ofskewback or tumbling inHandmade bricks see soft-mudbricksHatching & grinning irregularityof appearance due to the poorvertical alignment of the faces ofbricks in a wall surfaceHawk a small board, with ahandle in the centre of theunderside, used for holding inone hand a small quantify ofmortar ready for pointing with atrowelHeader the end face of astandard brickHod a three-sided box, mountedon a pole handle, used over theshoulder for carrying smallquantities of bricks or mortarHollow block concrete block inwhich voids run through from bedface to bed faceIncrement an increase ofdimension based on the length ofa standard brickInspection chamber chamberconstructed on a drain, sewer orpipe line with a removable cover topermit inspection, maintenance,clearance of blockages, etc, all

when operating from surface level(see also manhole)Insulation batt rectangular unitof resilient fibrous insulationmaterial of uniform thicknessused to fully fill the air space in acavity wallInsulation board rectangular unitof rigid insulation material ofuniform thickness used to partiallyfill the air space in a cavity wallInsulation material materialprimarily intended to reduce thepassage of heat through aconstructionIntrados the lower or inner curveof an arch (opposite extrados)Invert the lowest point on theinternal surface of a channel ortrough at any cross sectionIsometric a drawing, to scale,showing an oblique view of anobject from a high viewing pointJoint profile the shape of amortar joint finishJointer a tool used to form amortar joint profileJointing forming the finishedsurface profile of a mortar joint bytooling or raking as the workproceeds, without pointingKey brick the central brick at thecrown of an archKeyed brick a common brick,deeply grooved on the stretcherand header faces as a key forplaster or renderKiln a permanent enclosure inwhich clay bricks are fired. Thereare several designs, some providingfor continuous burningLateral load force actinghorizontally at right angles to theface of a wall. May be due to windforce, retained earth or fromassociated structureLeaf one of two parallel walls thatare tied together as a cavity wallLevel (1) the horizontality ofcourses of brickwork

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xiv GLOSSARY OF TERMS

Level (2) see spirit level andplumb levelLime (hydrated) a fine powderedmaterial, with no appreciablesetting and hardening properties,used to improve the workabilityand water retention of cement-based mortarsLime (hydraulic) a fine powderedmaterial which when mixed withwater slowly sets and hardens andbinds together to form a solidmaterial. Traditionally used as aconstituent of mortarLime putty slaked lime, sievedand mixed with water, possiblywith a little fine sand, to form awhite mortar. Traditionally used forthin joints in gauged archesLime stain (bleed or bloom)white insoluble calcarious depositson the face of brickwork derivedfrom Portland cement mortarswhich have been subjected tosevere wetting during setting andhardeningLine (1) a string line used toguide the setting of bricks to lineand levelLine (2) the straightness ofbrickworkLine block see corner blockLintel a component of reinforcedconcrete, steel or timber to supportbrickwork over an openingManhole an inspection chamberthat permits the entry of a personMarl a type of clay with a naturallime contentMasonry cement a pre-mixedblend of Portland cement, fillermaterial and an air entrainer usedto mix with sand and water toform a complete mortarMortar a mixture of sand,cement or lime, or a combinationof both, possibly with the inclusionof an air entrainer, that hardensafter application and is used forjointing brickwork or as render

Movement joint a continuoushorizontal or vertical joint inbrickwork filled with compressiblematerial to accommodatemovement due to moisture,thermal or structural effectsNVQ National VocationalQualification. A formal certificationof skill competencePacks of bricks bundles of brickssecured by bands or straps tofacilitate mechanical handlingParapet wall upper part of a wallthat bounds a roof, balcony,terrace or bridgePartition wall wall within abuilding to compartmentalise thespace within it. It may or may notsupport floors or roofsPerforated bricks extruded wire-cut bricks with holes through frombed face to bed facePerpends (perps) notionalvertical lines controlling theverticality of cross joints appearingin the face of a wallPier local thickening of a wall toimprove its stiffnessPigments powdered or liquidmaterials which may be added tomortar mixes in small quantities tomodify its colourPins flat bladed nails temporarilypressed into mortar joints to securebricklayers linePistol brick special shaped brickwith a recess in the lower bed to fitover support anglePlan a constructural drawingshowing a view of a building orobject in a horizontal plane. A floorplan shows the floor area of abuilding with walls in horizontalsectionPlasticiser powdered or liquidadmixture added to mortar mixesin controlled amounts to improveworkability by generating airbubbles. Also known as airentrainer

Plinth (1) visible projection orrecess at the base of a wall or pierPlinth (2) special shaped brickchamfered to provide for reductionin thickness between a plinth andthe rest of a wallPlugging chisel a stout chiselwith a narrow cutting edge forcutting out hardened mortar froma joint between bricksPlumb the verticality of brickworkPlumb level an instrument tocheck horizontality or verticality ofwork, consisting of a long,straight-edged casing fitted withtwo or more spirit levelsPointing finishing a mortar jointby raking out part of the jointingmortar, filling with additionalmortar, and tooling or otherwiseworking it to form the finishedjoint profilePolychromatic brickworkdecorative patterned work whichfeatures bricks of different coloursPortland cement a finepowdered material which, whenmixed with water, sets and bindstogether to form a hard, solidmaterial. It is used as a componentof mortar and concretePost tensioned brickworkreinforced brickwork in which thesteel is tensioned, usually by meansof tightening a nut on a threadedend of rod reinforcement, toartificially compress the brickworkand enhance its resistance tolateral loadPressed bricks bricks formed bypressing moist clay into shape byhydraulic pressProfile boards temporary timberboards erected outside the enclosingwalls of a structure at cornersand used to fix string lines whensetting-out foundations and wallsProfiles patent metal cornerposts which are temporarily set upat the corners and ends of walls to

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GLOSSARY OF TERMS xv

support string lines and assistbuilding the brickwork to line andlevelQuoin the external corner of awallQuoin block concrete block ofL shape on plan for maintainingbond at cornersRacking back temporarilyfinishing each brickwork course inits length short of the coursebelow so as to produce a steppeddiagonal line to be joined withlater workRadial special shaped brick ofcurved form for use in brickworkcurved on planReference panel a panel ofbrickwork built at thecommencement of a contract toset standards of appearance andworkmanshipReinforced brickwork brickworkincorporating steel wire or rodsto enhance its resistance to lateralloadRender mortar applied to a wallsurface as a finishRepointing the raking out of oldmortar and replacing it with new(see also pointing)Retaining wall a wall thatprovides lateral support to higherground at a change of levelReturns the areas of walling atpiers or recesses which are at rightangles to the general face of thewallReveal the area of walling at theside of an opening which is at rightangles to the general face of thewallReverse bond bonding in whichasymmetry of pattern is acceptedacross the width of an opening orat quoins of a wall in order toavoid broken bond in the workRough arch an arch of standardbricks jointed with tapered mortarjoints

Sample panel a panel ofbrickwork which may be built tocompare material andworkmanship with those of areference panelSand a fine aggregate whichforms the bulk of mortarSandlime brick see calciumsilicate brickScaffolding a temporaryframework, usually of tubular steelor aluminium, and timber boards togive access for construction workScale the proportional relationshipbetween a representation of anobject on a constructional drawingand its actual size, e.g. 1/10th fullsize � 1:10 � 1 represents 10Scutch a hammer with sharp-edged blade, or comb blade,set at right angles to the line of thehandle. Used for trimming a cutbrick to shapeSealant a stiff fluid materialwhich sets but does not harden.Used to exclude wind-driven rainfrom movement joints and arounddoor and window framesSection a constructional drawingshowing a view of the cut surfacethat would be seen if a building orobject was cut through, generallyverticallySemi-dry pressed bricks claybricks formed by pressing semi-dryor damp, ground granular clay intoshape by hydraulic pressShale a type of clay, oftenassociated with coal measuresSill the lower horizontal edge ofan openingSize see co-ordinating size, worksize and actual sizeSkewback brickwork, or specialshaped block, which provides aninclined surface from which anarch springsSoft-mud bricks bricks mouldedto shape from clay in a moist, mud-like state. Often handmade

Soldier a brick laid verticallyon end with the stretcher faceshowing in the surface of theworkSpecials bricks of special shapeor size used for the constructionof particular brickwork featuresSpirit level device for checkinghorizontality or verticalityconsisting of one or more sealedglass tubes, each containing liquidand an air bubble, mounted in aframeSpot board board up to 1 msquare on which fresh mortar isplaced ready for useSpringing plane at the end of anarch which springs from askewbackSquint special brick for theconstruction of non-right angledcorners (see also angle)Stock bricks soft-mud bricks,traditionally handmade, but nowoften machine mouldedStop special shaped brick toterminate runs of plinth, bullnoseor cant bricksStop end a three-sided box-shaped shoe of DPC materialsealed to the end of a DPC tray todivert the discharge of waterStorey rod gauge rod of storeyheight with additional marks toindicate features such as lintelbearings, sills, floor joists, etc.Stretcher the longer face of abrick showing in the surface of awallStrip foundation See footingSuction rate the tendency of abrick or block to absorb water fromthe mortar used for its beddingand jointing. Dense vitrified brickshave a low suction rate, porousbricks have a higher suction rateSulfate attack the chemicalreaction of soluble sulfates fromthe ground or certain types ofbricks with a chemical constituent

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xvi GLOSSARY OF TERMS

of Portland cement which results inexpansion of, and physical damageto, mortarTemplate full size pattern, usuallyof rigid sheet material, used as aguide for cutting or setting-outworkThroat (1) a groove formed in theunderside of a coping, projectingsill, or other projecting feature,parallel with its edge and intendedto cause water to drip off at thatpoint and not run back on to thesurface of the wall immediatelybelow.Throat (2) the narrowed part of aflue that is located between thetop of the fireplace and thechimney flueTies see wall tiesTingle plate a metal plate shapedto give intermediate support to aline when building long lengths ofbrickworkTolerance allowable variationbetween a specified dimension andan actual dimension

Trammel timber batten, pivotedat one end, used to set out curvedworkTrowel hand tool with a thin flatblade, usually diamond shaped, forapplying mortarTuck pointing a mortar joint finishsometimes used in the 17th, 18thand 19th century work in whichmortar joints are finished flush withthe face of the walling, tinted tomatch the bricks and then scoredwith a regular pattern of falsejoints to which thin ‘ribbons’ oflime putty are pressed to create theillusion of finely jointed, accuratelyset-out brickworkTumbling in a sloping featureformed by bricks laid in courses atright angles to the face of thesloped surfaceUnit of Competence formalrecognition of competence in aspecific task. Several Units buildtowards an NVQVerge sloping edge of a pitchedroof

Voussior a wedge-shaped brick orstone used in a gauged archWall joint vertical mortar jointbetween bricks within a wall andparallel to its faceWall ties a component, made ofmetal or plastic, either built intothe two leaves of a cavity wall tolink them, or used as a restraintfixing to tie back cladding to abackingWater absorption a measureof the density of a brick bycalculating the percentageincrease in the weight of asaturated brick compared withits dry weightWeep hole hole throughbrickwork, usually an unmortaredcross joint, through which watercan drain to its outer faceWork size the size of a brick orblock specified for its manufacture.It is derived from the co-ordinatingsize less the allowance for mortarjoints (see also co-ordinating sizeand actual size)

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1 PREPARATION AND PROTECTIONThis section deals with aspects ofbricklaying on site that are oftenleft to chance, or left to others.

Because they do not directlyinvolve the placing of bricks andmortar together in theconstruction of the actualbrickwork required, thesematters are sometimes regardedas of little importance –‘optional extras’ to be dealt withby someone other than thebricklayer. In reality poorlyprepared and presented materialwill hamper the achievement ofgood quality work and it is in

the best interest of thecraftsperson to see thatmaterials are correctly storedand handled before they areused. Similarly, it is in thecraftsperson’s interest to ensurethat when the work is completeit will be respected by othertrades and protected fromweather or damage while therest of the work is completed.Although these aspects of workmay be undertaken by someonein the building team other thanthe bricklayer, it is nonethelessimportant that it shall be done.

The building of referencepanels and sample panels is alsodealt with in this section. Theseagain are not unnecessary ‘extras’but give the chance for everyoneinvolved with the work to agreethe standard of quality that canbe expected with the particularbricks, mortar, and design detailsthat the building projectdemands. Time and effort spentin this exploratory work is veryworthwhile as it will avoid delayscaused by later dissatisfaction,disagreement and possibledemolition of unacceptable work.

1.1 REFERENCE AND SAMPLE PANELS

Bricklayers may be asked tobuild both reference andsample panels on site atvarious times. Bricklayers whounderstand why such panelsare built as well as how tobuild them can contributemuch to achieving goodquality brickwork andavoiding costly delays.

DEFINITIONSA reference panel will be builtbefore the facework begins inorder to determine designfeatures or to establish standardsof workmanship or the visualacceptability of bricks, or allthree.

Sample panels are built fromsubsequent deliveries of bricksfor comparison with those in theoriginal reference panel.

WHY REFERENCE PANELS AREREQUIRED

Their use can save time andmoney by helping to avoid orresolve disputes which may ariseover the quality of the bricks orbrickwork.

They may be required for anumber of distinct reasons:

1. For the architect to choose amortar joint colour and profileto suit the specified facingbricks.

2. To establish and provide, forthe duration of the contract, areference to the standard ofbrickwork which thecontractor can produceregularly and which will beacceptable to the architect.

3. Similarly, to provide areference for an acceptablelevel of minor or visible

surface blemishes such assmall surface cracks, chips,small pebbles and expansiveparticles of lime in the brickswhen they are delivered tosite (fig 1.1).

Figure 1.1. A reference panel toestablish an acceptable level of minorblemishes and proposed mortar colour.

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2 PREPARATION AND PROTECTION

It is a matter which cannot bejudged by examiningindividual bricks. Furtherreference is made in PAS70:2003(1).

4. Samples of special shapedbricks may be incorporatedin the reference panel toenable the designer toconsider any slight colourvariation between the specialand normal standard bricks(fig 1.2).

5. Reference panels may alsoinclude special featuressuch as soldier courses ornarrow piers so that anyproblem related to bricktolerances and workmanshipcan be resolved.

viewing in good natural daylightfrom a distance of 3 m. It shouldalso remain free from damage byvehicles, plant, mud or dirt.

When deciding on a locationfor a reference panel allow spacefor subsequent sample panelswhich should be orientated thesame way as the reference panelso that they can be viewedtogether in similar lightingconditions as well as from thesame distance of 3 m.

SELECTING BRICKS TO BUILD APANEL

PAS 70:2003(1) recommends theadoption of one of two methods:

1. ‘supplied by the manufactureror supplier so that they arereasonably representativeof the average quality ofthe whole order to bedelivered’ (this may often bethe simplest and mostappropriate method) or

2. ‘randomly sampled inaccordance with BS EN771-1(2). This gives precisestatistical methods ofsampling with whichmany site personnel maybe unfamiliar, in which caseit may be advisable toavoid duplication of effortby conducting thesampling in conjunctionwith the manufacturer orsupplier.

The methods are designed toselect a representative sample ofthe bricks delivered. Bricklayersshould not attempt to select thebest bricks and should discardonly those which they woulddiscard in practice during thecontract.

BUILDING THE PANELSeparate panels may be built tosatisfy the five requirementslisted above or one panel may berequired to meet more than oneof them.

Depending on therequirements, panels should bebuilt:

• on a firm concrete base andstabilised to prevent its beingknocked over. In practice thismay mean a 215 � 215 pierat each end of a half-brickthick panel which if largeenough to display 100 brickswill not be stable.

• to expose not less than 100bricks.

• to a standard which can bemaintained throughout thecontract. No attempt shouldbe made to build an‘exhibition panel’.

• discarding only those brickswhich would normally berejected by the bricklayerduring subsequent contructionof the contract brickwork.

• to the specified brick bond.• using the mortar and joint

profile specified.• to a vertical gauge of 4

courses to 300 mm, unlessotherwise specified, andplumb, level and aligned.

• with protection to prevent thetop of the wall becomingsaturated and stained.

• incorporating the specifiedDPC 150 mm above the slablevel to prevent rising dampstaining the brickwork and toprovide a demonstration of anagreed method for futurereference. Flexible DPCs shouldbe bedded on fresh mortar andnot laid dry (see Section 4.3‘Damp-proof courses’).

Reference panels provide usefulcontinuity in the event ofchanges of personnel, i.e.bricklayers, architects or sitesupervisors.

LOCATION OF REFERENCEPANELS

The panel should be built whereit will remain throughout thecontract, readily accessible for

Figure 1.2. Special shapes in areference panel.

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PROTECTION OF NEWLY BUILT BRICKWORK 3

Although the requirements dealtwith above and elsewhere in thissection are concerned withappearance, panels may berequired to explore or demonstrateconstructional matters such as theposition of wall ties, the fixing ofinsulation, lintels or DPC trays.

SAMPLE PANELSSample panels for comparisonwith the reference panel may berequired to be built if there is adispute about the quality of thebricks delivered to site.

The sample panels should bebuilt in the same way as thereference panel from bricksrandomly sampled in accordancewith BS EN 771-1(2). See thesecond method described under‘Selecting bricks to build a panel’above.

Sample panels should belocated so that they can be readilyand effectively compared with thereference panel. It is advisable tobuild them in the same plane

because different lightingconditions can result in differentappearances. It should also bepossible to view the sample panelfrom the recommended distanceof 3 m. Ideally provision should bemade to build sample panelsimmediately next to the referencepanel.

EXAMINING AND ASSESSINGREFERENCE AND SAMPLE

PANELSReference and sample panelsshould be viewed from about

3 m, as noted in the BritishStandard(1), and only aftersome days when thebrickwork has dried out,because damp brickwork isusually darker than drybrickwork.

References(1) BSI PAS 70:2003 ‘HD Clay

Bricks’ – Guide to appearance andsite measured dimensions andtolerances.

(2) BS EN 771-1:2003 Annex A.

KEY POINTS

■ Build reference panels in‘permanent’ position on a firmbase.

■ Panels must be viewed in goodlight at 3 m distance.

■ Allow for building sample panelsclose by.

■ Use bricks especially supplied bythe supplier or select at random.

■ Protect panels from saturation.

1.2 PROTECTION OF NEWLY BUILT BRICKWORK

The finished work of skilled,conscientious bricklayers canbe ruined for all time if it isnot protected. Protected fromwhat? Why and how?

RAINBricklayers expect rain or even hailor snow to interrupt their work.They may be only temporarilydiscomforted but their interruptedwork can be permanentlydisfigured unless protected. Thecauses are inevitable, the results

distressing, but protection issimple, requiring only forethoughtand preparation.

Even light rain falling on newlybuilt brickwork may saturate thesurface of the mortar and causethe very fine particles in thecement, lime and pigments toleach, changing the colour of themortar and giving rise to patchybrickwork.

The fine particles of free limein Portland cement and hydratedlime may leach and carbonate onthe brickwork as hard, shiny,

white crystals. Lime leaching isvery difficult to remove unlikemost efflorescence which is a softdeposit readily weathered awayby rain (fig 1.3).

Prevent saturationTo avoid such damage, protect thebrickwork before leaving the siteor when rain is imminent.A scaffold board or length of DPC,held in place by a few bricks, willoften be sufficient.

Although it is particularlyimportant to prevent rain

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Polythene sheeting, securedagainst sudden high winds byscaffold boards or bricks, iseffective. Ensure that there isenough to reach down to andprotect the lower courses of thenew work.

The scaffold boards nearest thebrickwork should be turned backif rain is expected otherwise thewall may become stained withbands of mortar splashes whichoften prove impossible to removesatisfactorily (fig 1.4).

Provide means of maintainingan airspace between thepolythene and brickwork as alack of ventilation may causecondensation which can be asdamaging as rain (fig 1.5).

Most competent bricklayersprotect their newly finished workbut they should also rememberto protect bricks stacked on thescaffold, especially if they have alow water absorbency (fig 1.6).

Such bricks can be difficult tolay if saturated. They tend to‘swim’ on the mortar bed as theyhave little initial suction toremove water from the mortarinterface.

Figure 1.3.Lime leaching.

entering perforations and frogs,even solid bricks should beprotected.

When severe or wind-drivenrain is expected it is advisable totake more elaborate precautions.

Shed rainwater

clear o

f brick

s

below

Maintain air space

Figure 1.4. Avoid mortar splashing.

Figure 1.5. Protection from rain.

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PROTECTION OF NEWLY BUILT BRICKWORK 5

Also the joints will cure moreslowly and when ironed or struckwill be of a different colour fromthose laid with drier bricks thuscausing an apparent colourchange in the brickwork.

FROSTIf mortar is frozen before it hastime to set it will remainpermanently friable and weakand have poor bond with thebricks. If this happens thebrickwork will have to be takendown and rebuilt.

The mortar in newly builtbrickwork can be protected fromfreezing by covering with hessianwhich in turn should beprotected by polythene sheetingfrom becoming wet and uselessas insulation. Alternatively,waterproofed insulating sheetswill give even better protection(fig 1.7).

SUN AND WINDIn hot, sunny weather, especiallywith drying winds, the mortarjoints may dry before the cementhas set and the mortar hasbonded adequately with thebricks. This is more likely tohappen with bricks of high waterabsorbency.

This risk can be reduced bycarefully draping the brickworkwith slightly damp hessian. If thehessian is too wet it may causestaining from the joints (fig 1.7).

PLANT AND PEOPLEUnprotected brick reveals, sills,arches, thresholds, steps andplinth courses may sufferaccidental mechanical damagefrom building plant or people.

Figure 1.6. Protect bricks on scaffolding.

Figure 1.7.

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Such damage is not onlyexpensive but often impossible torepair without leaving permanentscars.

Protect such features withstrips of plywood or hardboard orin the case of plinths withpolythene sheeting (fig 1.8).

WHOSE RESPONSIBILITY?Site supervisors are responsiblefor providing protective materialsand for giving instructions fortheir use.

BUTUltimately it is the bricklayer’sresponsibility, as the person onthe spot whose work is at risk, toprovide timely and effectiveprotection.

KEY POINTS

■ Always protect newly laidbrickwork from rain.

■ Protect it from frost in winter.■ Protect it from drying out quickly

in hot weather.

■ Leave an air space betweenprotective sheeting andbrickwork.

■ Turn back first scaffold board ifrain is likely.

■ Protect vulnerable brickworkfrom damage by people andplant.

1.3 HANDLING, STORAGE AND PROTECTION OF MATERIALS

Supervisors and bricklayersare responsible forimplementing managementpolicies for safe, carefuland efficient handling,storage and protection on

site in order to avoid wasteof time as well asmaterials. This section isconcerned particularly withavoiding damage to facingbricks.

Because the type of storage andmechanical plant available willvary from site to site it is essentialthat everyone is aware howhandling and storage are to beorganised.

Figure 1.8.

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HANDLING, STORAGE AND PROTECTION OF MATERIALS 7

STORING AND HANDLING OFBRICKS

There are two basic methods:

• Bricks may be located close tothe work place. This reducesthe risk of damage and theexpense of double handling.

• Alternatively a centralcompound (fig 1.9) providesfor better control of pilferingand misuse of all materialsinherent in the first method.

Bricks of special shapes and sizes‘Special’ bricks, being particularlyvaluable, should always be storedcentrally and easily identifiable forcollection as required (fig 1.11).Replacements for many typeswill not be available ‘off the shelf’(see ‘Storage’, p. 44, Section 2.9‘Bricks of special shapes andsizes’).

or placed directly by roughterrain fork lift trucks on agantry scaffold big enough totake at least three packs ofbricks (fig 1.12).

If packs have to be stacked onstructural floors they should beplaced close to columns awayfrom mid spans whilst allowingspace for access and working(fig 1.13).Storage areas must be

accessible to delivery vehicles andrelevant site plant and the bricksshould stand on a firm, level, welldrained puddle-free base, not incontact with soil of sulfate-bearing clinker or ashes (fig 1.10)nor where they can be mud-splashed by vehicles.

Figure 1.9. Storage compound – bricks,blocks and steel.

Figure 1.10. Storage of bricks.

Figure 1.11. Special shapes in pack.

Figure 1.12. Rough terrain fork lift withtelescopic mast.

Figure 1.13. Packs of bricks placed closeto columns.NOTE: for simplicity, scaffolding and safetyrails are not shown.

ProtectionGenerally, leave any polythenewrapping, banding or strappingin place. If the wrapping isremoved for inspection or none isprovided, replace or providealternative protection. If thebricks are saturated on deliveryprovide protection from furtherrain, but allow air to circulate anddry them before use.

Distribution from a central storePacks of bricks and blocksshould be transported tosuitably positioned flat drainedareas at work places or forfurther distribution. If the bricksare for use on upper floors theyshould be unloaded within thehandling radius of tower cranes

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A structural engineer shouldalways be consulted beforeloading out a floor. Typicalmaximum permissible loading onstructural floors and gantryscaffolds is 5–10 kN (1⁄2–1tonne) per m2.

NOTE:• One pack of typical facing

bricks is approximately0.75–1.00 tonne.

• One pack of typicalengineering bricks isapproximately 1.20 tonnes.

(The above is for information andgeneral guidance only).

Although the floor above willgive some protection to thebricks they will need extraprotection from water and wetconcrete draining through serviceholes.

Distribute no more than isnecessary for immediate use toany point, but heed any advicefrom manufacturers to blendbricks by supplying bricklayersfrom at least three packs (seeSection 3.2 ‘Blending facingbricks on site’).

Opening packs• The correct and safe way to

remove banding is by cuttingthe straps with snips or byplacing a chisel under thestrap as an anvil and strikingwith another chisel (fig 1.14).

• A common but not approvedmethod uses two fish-tail wallties (fig 1.15).

• Do not chop the band with abrick hammer or any toolwhich will damage the bricks.

• Immediately make bandinginto safe bundles and removefrom the work area. Loosebanding entangled round the

feet can cause seriousaccidents (fig 1.16).

• Polythene wrapping, removedcarefully and put on one side,can provide protectionelsewhere.

Loading-out for the bricklayer• Lay out alternate stacks of

bricks and spot boards alongthe face sides of walls andapproximately 600 mm fromthem.

• Make a level base for eachstack, possibly using rejectedmaterials.

• Stack bricks with frog orperforation uppermost, foreasy handling by thebricklayer.

• At the end of work protecteach stack from rain.

• Supply stacks by drawingfrom as many packs aspossible, but at least three.

Remove vertical slices of bricksrather than horizontal layers,in order to blend them well(fig 1.17).

Moving to the next working place• On completion of a lift move

all materials to the next workarea ready for the next lift.Bricks left on the scaffoldmight be tipped off andwasted.

HANDLING, STORING ANDPROTECTING OTHER

MATERIALS

Cement and lime in bags• Unload without damaging the

bags, stack so thatconsignments can be used inorder of delivery and protect

Figure 1.14. Cutting brick banding with‘snips’.

Figure 1.15. Incorrect cutting of bands.

Figure 1.16a. Brick strapping – a‘hazard’.

Figure 1.16b. Brick strapping made safe.

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HANDLING, STORAGE AND PROTECTION OF MATERIALS 9

from rain, frost and soil anddamp walls. Both lime andcement deteriorate quicklywhen damp, producingmortar with inferior strength,adhesion and durability (seeSection 4.1 ‘Mortars’).

Sand and premixed lime:sand(coarse stuff) for mortars• Store on a hard, clean,

drained base, separatingdifferent types of sand andprotect from rain especially iffrost is imminent.Contaminated sand andcoarse stuff may produce

mortars with inferior strength,adhesion, durability andappearance.

• Coarse stuff must also beprotected from rain andwind, which may erode thefine particles of cement, limeand pigments causinga marked change inmortar colour (see Section 4.1‘Mortars’).

Flexible damp-proof courses• Store rolls on end, no more

than three packs high toavoid distortion.

• Protect bitumen and otherthermoplastic materials fromdirect heat.

• In cold weather storesufficient overnight in a warmplace for use the followingday as some DPCs are difficultto roll out when cold (seeSection 4.3 ‘Damp-proofcourses’).

Ancillary components• Lintels, wall ties, thermal

insulation batts and boards,DPC adhesives, movementjoint fillers and sealants are

Supply stacksfrom at leastthree packs

Remove bricksin vertical slicesfor best blend

Remove bandingto a safe place

Replaceprotection totop of packs

Figure 1.17.

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examples of materials whichshould be handled, storedand protected with care inorder to avoid damage, loss,distortion and deterioration.

• Read and carefully follow themanufacturers’ instructions.

• Additional wooden palletsmay be necessary fortransferring bags of cement,lintels, DPCs or othermaterials from openedpacks in the centralcompound.

Further reading• BS 5628-3:2001 ‘Code of practice

for use of masonry – Part 3:Materials and components,design and workmanship’.

• ‘Brickwork – good site practice’Knight. The Brick DevelopmentAssociation 1991.

• Sections 2.9, 3.2, 4.1, 4.3, 4.4 ofthis publication.

KEY POINTS

■ Central storage permits bettercontrol

■ Stand bricks on flat, well-drainedsurfaces.

■ Protect bricks from saturationand contamination.

■ Take special care of specialshaped bricks.

■ Locate packs stacked on concretefloors close to supporting columnsbut always with the advice of astructural or civil engineer.

■ Clear away potentially dangerouscut strapping and banding.

■ Protect all mortar materials■ Follow manufacturers’

instructions for handling andprotection of all materials.

1.4 ESTIMATING QUANTITIES OF BRICKS AND MORTAR

The quantities of bricks and mortarin the following tables have beenarrived at by calculation assumingthat standard bricks with a worksize of 215 � 102.5 � 65 mmare used and that the mortarjoints are solidly filled andnominally 10 mm wide.

For the mortar, five figures aregiven for each wall thickness,depending on the form of thebricks being used and how theyare laid, i.e.:

1. Solid bricks2. Perforated wire-cut bricks

(It is difficult to estimate howmuch mortar enters theperforations as this will varywith the pattern and size ofthe holes. A 5% increase overthe figure for solid bricks isassumed)

3. Bricks with a shallow frog(In which the frog is about

Quantity of bricks and mortar per square metre of wall surface

Wall Number Mortar (cubic metre)thickness of (mm) bricks Solid Perforated Shallow Deep Deep

wire cut frog frog frog (frog (frog up) down)

102.5 59.26 0.018 0.019 0.022 0.030 0.023215 118.52 0.045 0.047 0.054 0.068 0.055327.5 177.78 0.078 0.082 0.086 0.107 0.088440 237.04 0.101 0.106 0.118 0.146 0.120

Quantity of mortar per 1000 bricks

Wall Mortar (cubic metre)thickness (mm) Solid Perforated Shallow Deep frog Deep frog

wire cut frog (frog up) (frog down)

102.5 0.30 0.32 0.37 0.50 0.39215 0.38 0.40 0.46 0.58 0.47327.5 0.41 0.43 0.48 0.60 0.49440 0.42 0.44 0.50 0.62 0.51

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ESTIMATING QUANTITIES OF BRICKS AND MORTAR 11

5% of the gross volume ofthe brick)

4. Bricks with a deep frog,laid frog up (In which thefrog is up to 20% of the grossvolume of the brick, e.g. apressed Fletton brick)

5. Bricks with a deep frog,laid frog down

ALLOWANCE FOR HANDLINGAND WASTAGE

The quantities of bricks andmortar given in the tables arebased on calculation. In practiceallowance must be made forhandling and wastage. Anincrease of 5% is generallyallowed for the quantity of bricksand 10% for mortar.

A worked exampleEstimate the bricks and mortarrequired to build a freestandingwall 215 mm thick, 25 m longand 1.8 m high from the top ofthe foundation to the undersideof the coping units.

Surface area of the brickwork:25 m � 1.8 m � 45 m2

Number of perforated wire-cutbricks for 215 mm thickness:

45 � 118.52 � 5333.45% wastage allowance � 266.6Total � 5600.0

Volume of mortar– calculated on wall dimensions:

45 � 0.047 � 2.11510% wastage allowance � 0.211Total � 2.326 m3

– calculated on number ofbricks:5333 � 0.4 � 2.13310% wastage allowance � 0.213Total � 2.346 m3

SUMMARY 5600 bricks and21⁄3 m3 mortar.

THE VOLUME OF CEMENT INBAGS

Mortars are normally mixed on siteby volume, but cement is suppliedby weight in bags of 25 kg.

The density of OrdinaryPortland Cement can be1200–1400 kg/m3. It is generally

taken as 1400 kg/m3 if morespecific information is notavailable.

Based on a density of1400 kg/m3 the volume ofcement in a 25 kg bag is0.0175 m3 (17.5 litres) which isequal in volume to a 260 mmcube.

For mixing mortar on site it isconvenient if a box is made equalto the volume of a bag ofcement, then this can be used asan accurate measure for the otherconstituents of a mortar mix, e.g.a 25 kg bag of cement � 1 boxmeasure of hydrated lime � 6box measures of sand makes a1:1:6 cement:lime:sand mortar.

Boxes can be made with nofixed bottom to save lifting andtipping contents out (fig 6.32).

REMEMBER that becausebinder materials (cement and anylime) in a mortar mix occupy thespace that naturally occursbetween the particles of thesand, the volume of the mortar isthe same as that of the sand, notthe volume of sand plus thevolumes of the cement and thelime (if any).

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2 BRICKLAYING TECHNIQUESThis section deals with basicbricklaying skills common to all

brickwork assemblies – settingout and control of the regularity

of the work, the use of tools,forming joints, etc.

2.1 SETTING-OUT FACEWORK – STRETCHER HALF-BOND

Face brickwork should beset-out at the lowestpracticable level, ideallybelow finished ground level,before bricklaying begins,otherwise ill-considereddecisions may have to bemade later regarding bondingand cutting, particularly atwindow and door openings.The result may be a lastingmonument of poorworkmanship.

Setting-out facework isnormally the responsibilityof the supervising bricklayerwho will, after consultingthe architect, determine thedetailed bond pattern andthe location of any broken orreverse bond.

Setting-out the brickwork isdifferent from setting-out thebuilding which is done beforeexcavation begins.

OBJECTIVESOne of the main purposes ofsetting-out facework is to createa matching and balancedappearance of brickworkparticularly at the reveals oneither side of door and windowopenings and ends of walls.

An understanding of therelationship between openingsand the bond pattern, if sharedby bricklayers, site supervisorsand architects will minimisedisappointments and delays.

BRICK DIMENSIONSBrickwork should be setout using the co-ordinatingsize of the length of a brick,e.g. 225 mm (215 mm worksize � 10 mm nominal jointfor bricks to BS EN 771-1)(1)

(fig 2.1).The above co-ordinating

and work sizes are those ofthe bricks most widely usedin the UK, but the specificationmay call for the use of bricksof other sizes. In this case,

WORK SIZE(co-ordinating size lessnominal 10 mm joint)

ACTUAL SIZE(as measured)

225 112.5

This is a general rule which isto be applied to faceworkcontaining window and dooropenings. It is not necessaryto apply it rigidly in allcircumstances, e.g. a free-standing wall for whichthe bricks have all beendelivered at one time.

Although the basic principles of setting-outapply to all brickwork, of whatever bond,this section deals specifically with stretcherhalf-bond only.

CO-ORDINATINGSIZE

Used for design andsetting-out

215

e.g. 213

e.g. 217

e.g. 100.5

e.g. 104.5

102.5

Figure 2.1.

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SETTING-OUT FACEWORK – STRETCHER HALF-BOND 13

setting-out should be done toa corresponding system ofdimensions, e.g. if the work sizeof a brick is 190 � 90 � 65 mma nominal 10 mm is allowedfor mortar joints giving a co-ordinating size of200 � 100 � 75 mm.

• If brickwork is set-outusing the average actualsize of the bricks in thefirst delivery, difficultiesmay occur if subsequentdeliveries differ.

DESIGNBroken bond and possiblywasteful cutting can be avoidedif the overall length of walls andthe widths of doors, windowopenings and brickworkbetween the openings are allmultiples of a brick stretcher.The bonding either side ofreveals will also matchsymmetrically at each course(fig 2.2). (This applies to stretcherhalf-bond and English bond butnot to others such as Flemishand Dutch bond.)

In practice, this ideal situationseldom occurs and a satisfactorysolution is dependent onbricklaying skills.

PERPENDSThe bonding pattern should beset out at ground level so thatthe first few courses establishperpends for the full height ofthe wall and any problems maybe resolved with the architect orsite supervisors.

Pencil tick marks made on thebrick face should be light anddiscreet (fig 2.3). Heavy marksover the full height of the brickcan spoil the finished brickwork.A test should be made on thetype of brick to be used beforebricklaying begins as pencil marksare more conspicuous and moredifficult to remove on some typesof bricks than others.

The verticality of perpends infacing brickwork is as visuallyimportant as the horizontality ofcourses. In practice satisfactoryverticality is achieved byplumbing about every fourth orfifth perpend.

REVEALSThe positions of all windowopenings and ‘reveal’ bricksshould be identified when settingout the first few courses (fig 2.4).This ensures that perpends cancontinue unbroken for the fullheight of the wall.

Broken bondReveal bricks provide fixed pointsbetween which the bonding isset out (fig 2.5). The usuallyshort lengths of brickworkbetween windows offer littlescope for ‘adjusting’ the widths

3Bricks

3Bricks

5Bricks

5Bricks

3Bricks

Figure 2.2. ‘Ideal’ dimensions – whole numbers of bricks and symmetrical reveals.

Figure 2.3. Plumbing perpends.

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14 BRICKLAYING TECHNIQUES

of cross joints in order to avoidbroken bond.

Broken bond can sometimesbe avoided by ‘tightening’ or‘opening’ the joints. In doing sobricklayers should work to thestandard co-ordinating size of225 mm (i.e. 215 � 10 mm) ratherthan the actual size of the bricks(see ‘Brick Dimensions’ above).

Reverse bondInstead of slightly and evenlyadjusting cross joints to avoidbroken bond it may be decided,with the agreement of thearchitect, to use reverse bond.This allows bricks in reveals eitherside of openings or at each endof a wall to be asymmetrical. Bydoing so it ignores the mainprinciple of setting out face

work, which is to create abalanced appearance, butsometimes architects preferreverse bond to broken bond.

Broken bond occurs below awindow opening, as the result ofsetting-out to achieve symmetryof reveal bricks (fig 2.6a).

Window ‘reveal’ brickslocated at ground levelbefore bricklaying begins

Door opening locatedfrom drawings

Figure 2.5. Setting-out openings atground level.

Figure 2.6a. Broken bond.

Opening4½ bricks

Position ofwindow opening

to be built

Plumbedperpendsdpc

‘reveal’

‘reveal’ brickspositioned atground level

Figure 2.4. Setting-out window positionat ground level.

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SETTING-OUT FACEWORK – STRETCHER HALF-BOND 15

Broken bond can be avoidedby using reverse bond (fig 2.6b).It is, however, unlikely to beacceptable if contrastingcoloured reveal bricks areused as a decorative feature.Alternative solutions are shownin (fig 2.8).

Bricks should be spaced ‘dry’from each end of a wall whichhas no openings, to enable anagreed bonding to be reached(fig 2.7).

Figure 2.7. A wall without openings –bricks spaced out ‘dry’.

Opening4½ bricks

Figure 2.6b. Reverse bond.

Figure 2.8d. Reversing the bond at each end of a wall may also be considered preferableto broken bond.

Figure 2.8c. However, some architects may prefer three-quarter bricks at each end.

Figure 2.8b. In this situation a bricklayer will usually use broken bond, located centrally.

Figure 2.8a. The ideal solution is seldom possible.

ALTERNATIVE SOLUTIONS

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POLYCHROMATIC BRICKWORKWhere different coloured bricks areused, especially in band courses,check for differences in averagework sizes between them to avoidexcessively wide, narrow or badlyaligned cross joints. Such problemscan usually be avoided by setting-out to 225 mm increments ratherthan attempting to maintain10 mm wide cross joints.

Reference(1) BS EN 771-1:2003 Table NA.1

‘Coordinating and work sizes ofclay brick’.

KEY POINTS

■ Locate the position ofopenings and the associatedreveal bricks above whensetting out at ground leveland before commencingbricklaying.

■ Base setting-out at groundlevel on the 225 mmco-ordinating dimension NOT theactual sizes of the bricks in thefirst delivery.

■ Run out facing bricks ‘drybonded’ between the revealsand quoins.

■ Plumb the perpends of brokenbond from ground level upwards.

■ ‘Tighten’ or ‘open’ cross jointsslightly and evenly in order toavoid broken bond wherepossible.

■ Generally centralise broken bondin walling and below windowsunless the use of three-quarterbricks at each end is preferredby the architect.

■ Reverse bond may be preferredby some architects in order toavoid broken bond.

2.2 GAUGE AND STOREY RODS

Bricklayers, as part of aconstruction team, have toco-ordinate or ‘work in’ withother building components,particularly doors andwindows.

One of the most importantco-ordinating processes isknown as ‘keeping the gauge’.

KEEPING TO GAUGEThis refers to working betweentwo given points, A and B, andkeeping the bed joints of eventhickness (fig 2.9).

STANDARD GAUGE• The standard gauge is four

courses to 300 mm (i.e. 4 �75 mm, the brick co-ordinating size) (fig 2.10).

• These standard bricks aremade to a work size of65 mm high (the intendedor target size) which is equalto the co-ordinating size of

B

A

65

65

65

65

75

10

10

10

10

75

4 courses= 300 mm

75

75

Figure 2.9.Gauge and even jointthickness.

Figure 2.10. Standard gauge.

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GAUGE AND STOREY RODS 17

75 mm less a 10 mmnominal joint (fig 2.10).

• The actual size will be a littlemore or less than the worksize but the standard gaugemust be maintained even

though the joints will be alittle less or more than thenominal 10 mm. A goodbricklayer will ensure that allbed joints are regularin appearance (fig 2.11).

• Standard gauge andregular bed joints takeprecedence over 10 mmjoints.

The specification may call forthe use of bricks of a size otherthan that given in BS EN 771-1(1).For example thinner bricks,sometimes referred to as Tudorbricks, may be 41 mm high andwould be specified to be laid toa gauge of 6 courses to 300 mm,i.e. with a nominal bed joint of9 mm.

GAUGE RODSGauge rods are made and usedto maintain gauge and regularbed joints. They are made from atimber lath (typically 50 � 25 mmnominal). The length dependson the height of componentssuch as doors and windows.

The standard gauge is markedon one side and one edge.

Making a gauge rodAccuracy is essential and isachieved by using runningdimensions (fig 2.12a).

• Extend a tape from one endof the lath.

• Make pencil marks every300 mm (300, 600, 900, etc.as running dimensions).

• Sub-divide these incrementsinto 75 mm increments(75, 150 and 225 mm).

• Use a square to ‘square off’the pencil marks at rightangles to the sides of the lath(fig 2.12b).

• With a saw make permanentgauge cuts. NOTE: an oldwoodworking squareprovides a good guidingedge for the saw.

4 co

urse

s to

300

mm

Work size is 65 mmand nominal joint is10 mm

When average actualsize is more than worksize, then thinner butregular joints

When average actualsize is less than worksize, then thicker butregular joints

Figure 2.11. Building to standard gauge – maintaining regular bed joints.

Figure 2.12b. Permanent gauge cuts.

300 600 900

Figure 2.12a. Marking ‘running dimensions’.

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STOREY RODS• Storey rods contain other

useful information in additionto the standard gauge.

• The heights of walls, windowand door heads and sills canbe marked on the sideopposite to the standardgauge. These are oftenidentified by an inverted Vwith an abbreviateddescription. The height abovedatum is also included as auseful on-site reminder(fig 2.13).

• An alternative method is tomark the bed line saw cut onthe same side as the standardgauge and use a colour code,e.g. blue for sills and seatings,and red for lintels and archspringings.

USING GAUGE/STOREY RODS• Gauging is usually taken from

a fixed datum, normally atDPC level (fig 2.14).

• A nail is often simply driveninto a joint but a 50 � 25 mmbatten screwed into convenientjoints gives a more solid basefor the gauge rod.

• Check the gauge every courseas quoins are raised.

• When checking a quoin forgauge, check the brick forgauge before plumbing andlevelling (fig 2.15a) because:

(a) if low to gauge, plumbingand levelling would bepointless as the brick mustbe removed and rebedded.

(b) if the gauge is checkedfirst and found correctthen the quoin brick canbe levelled, plumbed andaligned without alteringthe gauge (fig 2.15b).

‘Working in’ other components• A gauge rod, level and

straight edge are used to‘work in’ and positioncomponents such as windowand door frames (fig 2.16a).

Figure 2.13. Storey rods.

• For accuracy they should bepositioned and gauged fromthe top down.

• Once the frame is positionedand supported the gauge canbe marked, on the sidetowards the bricks, as an extracheck when the brickwork isbeing built (fig 2.16b).

Figure 2.14. Gauging from a fixed datum.

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GAUGE AND STOREY RODS 19

Reference(1) BS EN 771-1:2003 Table NA.1 in

National Annex.

Figure 2.15a. Checking gauge of quoin brick.

Figure 2.16b. Gauge marked on back of door frame.

Figure 2.16a. ‘Working in’ a door frame.

Figure 2.15b. Plumbing quoin brick.

KEY POINTS

■ Use running measurements tomark gauge/storey rod accurately.

■ Use a square to mark gauge linesacross the lath.

■ Set-out the gauge from thetop down on components to bebuilt in.

■ Store gauge rods flat and dry.They are important pieces ofequipment for producing goodquality brickwork and should betreated as such.

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Existing buildingsIf the gauge of new work isrequired to match that ofthe existing brickwork, preparea gauge rod from the existingwall.

Work below ground level• Drive a peg into the ground to

indicate DPC level (fig 2.17).• With a level, straight edge

(if necessary) and a gaugerod, gauge down into thefoundation trenches.

• If there is not a wholenumber of 75 mm courses,any thickened bed joints orsplit course must be at thebottom of the brickwork.

• The object is to ensure that abed joint will coincide withDPC level.

These apply both to straightand curved walls, but theprocedures detailed in thissection are based on straightwalls (for curved brickworksee Section 5.7).

Quoins must be raised ascontrol points before lining-incan begin.

BUILDING AN ACCURATECORNER

When the corners of thebrickwork have been marked onthe foundation concrete then:

• Lay out materials within easyreach, without obstructingthe bricklayer.

• Run out the correct bond, dry,before any bricks are laid.

• Ensure that a datum peg,marked with the DPC level,is within reach of the quoinbrick (fig 2.19).

• Lay the quoin brick first.Push it down to gauge and‘level by eye’ (fig 2.20).Select reasonably squareand regular quoin bricks tomake it easier to build anaccurate corner.

Figure 2.17. Gauging downfrom datum.

2.3 LINE, LEVEL AND PLUMB

Whether building with bricksor blocks the same basicprocedures apply.

• The construction of controlpoints.

• Lining-in between thesepoints (fig 2.18).

Corners ascontrol points

Line betweencontrol points

Figure 2.18. Basic procedure.

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LINE, LEVEL AND PLUMB 21

The trend, in practice, to buildcorners up to eighteencourses high should beavoided as it entails morework to level and line usinga spirit level and, where itleads to toothing (fig 2.23c),to poorly filled weak jointsand a poor appearance.Furthermore, it is quicker to‘run the line’ than to level andrange quoin courses.

Figure 2.19.Levelling quoinfrom datum.

Figure 2.21. Levellingfrom the quoin brick.

Figure 2.20. Laying thequoin brick.

CheckgaugeCheck brick

level by eye

Eye downboth facesin line withwork below

• Level from the quoin brick, asthe first course cannot beplumbed (fig 2.21).

• The number of courses to beraised to complete the cornersis the same as the totalnumber of bricks in the firstcourse at the corner (fig 2.22).

6 bricks in firstcourse at cornergives 6 courseshigh

• Note that the control point forplumb and gauge is the quoinbrick and the more bricks thatare laid out from it the morelikely they are to run out ofline (fig 2.23a). It is thereforegood practice to raise smallcorners, run in the bricksbetween them and then tocontinue raising them by thesame amount (fig 2.23b). Figure 2.22. A practical tip.

Foundation

Quoin brick

Check gaugewith spiritlevel

Datum peg

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• The second course can belaid, quoin brick first. Keepa check on vertical gauge bylevelling out from the quoinbrick in both directions atevery course. At this stage,plumbing the corner can beonly approximate as there arenot many bricks to place thelevel against, so restrain thebottom of the level with thefoot and hold the upper part.Always plumb the same partof the corner, otherwise smallirregularities in the bricks maycause inaccuracies. Hold thespirit level plumb and gentlytap the bricks towards oraway from the level, until thefull height of the brick, notjust one corner, is in contactwith the level, and the bubblereads plumb (fig 2.24).Sometimes an irregularbrick will have to be knockedout of level to bring its faceplumb.

Line pushed outof true by poor‘lining-in’ ofcorner

Line of wall Bricklayer´sline

Repeat

Repeat

Raise cornersrun in bricksbetween

Figure 2.23c. Building corners –unsatisfactory method.

Figure 2.23b. Building corners –recommended method.

Figure 2.23a. The danger of long corners.

Hand on top

Foot at bottom

Tapping brick backFigure 2.24. Tapping brick to the level.

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Subsequent courses are laid onthe corner, racking back asnecessary, in the followingsequence:

• Bed the quoin brick to gaugeand level ‘by eye’.

• Check it for gauge and levelin both directions.

• Complete each quoin course,levelling from the quoin brickbefore the mortar bedstiffens.

• Plumb both faces of thequoin.

• Check cross joint thicknessand perpends.

• ‘Range in’ both faces usingthe spirit level to check faceplane alignment (fig 2.25).

• Double-check plumbing onboth faces in case they havebeen disturbed.

The student should consciously‘train his eye’ to estimate bed jointthickness, level and plumbaccurately to minimise theadjustment needed upon checkingwith gauge rod and level.

PLUMBING PIERSWhen building piers, avoidspreading excessive beddingmortar as the heavy tappingneeded will disturb the coursesbelow which will have had littletime to stiffen.

With isolated piers it is goodpractice to get a ‘turn of thebubble’ batter on both sides. Thisshould prevent the cross jointgetting larger and the piers from‘hanging out’ towards the top(fig 2.26).

Another method is to plumbonce in each direction and tocheck the opposite face with atape.

USING PROFILESThe use of patent profileseliminates the need for raisingquoins and can give greateraccuracy because they are placeddirectly at the control point andthe line is fixed to them(fig 2.27).

NOTE: Patent profiles of variouseffective designs are produced bydifferent manufacturers. The toolillustrated in diagrams in thisbook is only intended as a typicalexample and no inference shouldbe drawn that this particulardesign is approved or preferredby the authors.

Some other designs haveadditional features and/oraccessory fittings that extendtheir usefulness in assistingaccurate and well controlledbricklaying.

MAINTAINING LEVELThe level of the wall ismaintained by accurate gaugingfrom the same fixed datumwhich is usually DPC level. Thereshould be a datum peg at eachcontrol point or corner and thebricklayers should work downfrom them in substructure andup from them in superstructure

Figure 2.25. Aligning the ‘racking back’.

Figure 2.26. Plumbing piers.

Plumbbothsides

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Cramped intoraked verticaljoint

Screws toplumb profile

Special clip cornerblock to locate line

brick wall as soon as possible asdatum pegs often becomedislodged on site.

USING A GAUGE RODIf the storey height of a buildingdoes not work to gauge, orexisting brickwork has to bematched, then a ‘one-off’ gaugeor storey rod should be made upto suit each unique situation ofnon-standard gauge. The use ofsuch a non-standard gauge orstorey rod, where this is

necessary, allows the opening orclosing of a gauge to be gradualand not noticeable. The storeyrod can be marked to showcritical heights such as sill,lintel, joists and plate levels.More information on themaking and use of rods is givenin section 2.2 ‘Gauge andstorey rods’.

If the corners are built asshown in fig 2.29 and the line isfixed to the same course heightthen the wall built between thecorners will be level.

Figure 2.27. A typical patent profile.

Figure 2.28. Gauging down belowdatum.

(fig 2.28). If there is not a wholenumber of 75 mm coursesbetween datum and stripfoundations, any thickened bedjoints or split courses must be atthe bottom of the brickwork. It isadvisable to set a datum on the

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LINING IN PROCEDURESThe lineIt is essential to use a goodquality line, either of cotton,hemp or nylon. Preferences are amatter for the individual, but foraccuracy the line should be light,to prevent sag, and durable so asnot to rot if left damp, andwithout knots.

If lines cannot be spliced, theknot should be wound onto thepin. When the remaining lengthbecomes too short the whole lineshould be replaced.

The corner blockTo avoid ‘pin-holes’ in a quointhe line can be held to the cornerwith blocks which are usuallymade from wood (fig 2.30). Theline is pulled through the saw cutand taken once under the line,and through the saw cut again.Hitch the line round the pin toprevent its hanging down too far(fig 2.31).

Place the corner blocklengthways to the direction tobe run. Keep the line taut toprevent the block from falling.Pull the line through the block asbefore. The amount of tensionnecessary to keep the line tautand with no visible sag whensighted, will depend on thelength of the wall betweencorners (fig 2.32).

Both corners builtto same heightand gauge

Datum pegs atsame level

Figure 2.29. Two corners ready for ‘running in’.

Pass line through sawcut,round block, downbetween block and mainstretch, round block andthrough sawcut again

Saw cut

NOTE: the actual sizeis to suit individualpreferences

approx. 80 m

m

approx.40 mm

Figure 2.30. A typical cornerblock.

Figure 2.31. Using corner blocks.

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A corner block on the top courseIf the mortar is not completelyset the top brick may becomedislodged when the corner lineis raised to the last course,

especially on long walls. This canbe avoided by weighting the topbrick with a few others placeddry (fig 2.33).

Checking the general alignmentof cornersThe bricklayers should check thatthe quoin courses ‘follow theline’ each time it is raised.

Running-in to the lineBricklayers should positionthemselves so that they can sightboth down and across the line(fig 2.34). When eyeing downthey should be able ‘to just seethe light’ between the brick andthe line. Some bricklayers thinkof the gap as the thickness of atrowel. The arris should nevertouch the line. The bottom arrisshould align with the wall facebelow. When eyeing across theline the top of the brick shouldnot project above the line.

NOTE: it is usually the ‘righthand bricklayer’ on a wall whotensions a line.

If the line is stretched over along length and sags due to itsself-weight, a tingle plate shouldbe used to support the line asdescribed in section 2.4 ‘Verticalperpends’ and section 5.1‘Copings and Cappings’.

Irregular shaped bricksLaying some handmade andstock bricks requires experienceand skill above that required tolay more regularly shaped bricks.Surface irregularities must notinterfere with the line.

Internal cornersHere the quoin brick is not theonly major plumbing point. Theadjacent brick is also importantbecause the line is often fixed100 mm or more from theinternal angle (fig 2.35).

Figure 2.32.

Line ontop course Bricks placed

‘dry’ to stabilisetop brick

Figure 2.33. A cornerblock on the top course.

Brick NOTtouching line

Brick NOTabove line

Figure 2.34.

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A slightly larger corner willneed to be raised because theline will need a few bricks ascounterweights to preventdislodgement especially on longwalls. On the top course, the lineshould be taken over the back ofthe wall and the line held in

position by a brick placed dry onthe corner (fig 2.36).

Maintaining piers in alignmentPiers in a line should never bebuilt separately. The corner orfirst piers at each end shouldbe raised ahead of the

remainder and a line strungbetween. The piers shouldalways be a course or sobehind the main wall so thata tight line can be pulledthrough the face of theinfilling panels of brickwork(fig 2.37).

Corner blocksand line toalign piers

Line and pins toalign main wall

Figure 2.37. Maintainingpiers in alignment.

KEY POINTS

■ Always set out brickwork fromprofiles or grid lines. Do not justfollow the centre of the trench orassume that steel or concretecolumns are correctly positioned.

■ Run out a wall in dry bricks tolocate openings, broken bondand perpend plumbing pointsbefore you start laying bricks.

■ Always work from datums tokeep gauge of brickwork correctall round the building.

■ Keep to standard gauge for newwork.

■ Always make a storey rod inpreference to checking with a tapeto keep vertical gauge constant.

■ Raise small quoins throughout aworking day.

■ Always rack back when raising aquoin. Avoid toothing.

■ Keep your foot on the bottom ofthe spirit level when plumbing aquoin.

■ Always keep a tight line.■ Make broken bond as

inconspicuous as possible(i.e. two equal cuts over onecut in alternate courses ispreferable to a single cutin every course in stretcherbond).

■ Plumb perpends every fourth orfifth brick along a course.

■ Always plumb the perpends ofbroken bond.

Face side

Figure 2.36. Top courseof internal corner.

Face side

Pins intocross joints

Figure 2.35. Pins atinternal corners.

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MAINTAINING PERPENDSWHEN RUNNING THE LINE

Once the corners have been builtthe bricklayers ‘run the line’, thatis they build the walling betweenthe corners. By positioning everyfourth or fifth brick exactly abovethe corresponding bricks in lowercourses the ‘perps’ will remainconstant in position.

If the ‘perps’ are notconsciously aligned they maygradually close up on one part ofthe walling whilst opening on thenext part especially if onebricklayer is quicker than the rest.This might result in one bricklayerhaving to ‘crop’ or cut bricks to

2.4 VERTICAL PERPENDS

LinePlumb-uptingle brick

Brick batlocatestingle

Tingle plate

Bricklayer’s line

Figure 2.38. Use of a tingle brick to prevent ‘travelling’ perps.

achieve a fit in his part of thewall whilst another may have toincrease the thickness of his‘perps’ to compensate for theresulting discrepancies.

The methodThe difficulties, as described, caneasily be overcome with care andforethought.

Firstly, divide the length of thewall into equal sections (normallytwo) by the use of a tingle, adevice for taking up the slack ordrop inherent in a line pulledbetween two distant points. Thetingle and its use is illustratedand described in section 5.1‘Copings and Cappings’.

The tingle is placed on a brickbedded near the centre of the runof walling. Plumbing this tinglebrick up the wall effectively dividesthe wall into two sections, causingthe bricklayers to adjust only theperpends within their ownsections. This will help to preventthe perpends from ‘travelling’across the facework (fig 2.38).

Finally, check, at frequentintervals horizontally, that theperpends are vertically abovethose in the courses below.

In good quality facework thevisible vertical joints inalternate courses should havethe general appearance ofrising vertically one abovethe other for the full height ofthe building without‘wandering’. Although thismay appear to be a simplematter, it can be achievedonly if supervisors andbricklayers think ahead andexercise care and attention.

DEFINITIONThe visible lines of vertical orperpendicular cross jointsbetween bricks are commonlycalled ‘perpends’ or ‘perps’.

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VERTICAL PERPENDS 29

BELOW GROUND LEVELWhenever possible, the actionsnecessary to maintain verticalperpends should be consideredwhile construction is belowground level and beforefacework begins. Door andwindow jambs should beaccurately located and the‘reveal’ bricks plumbed upwardsso that the perpends may bemaintained vertically and will notbe required to ‘travel’ across thefacework to the correct positionfor the reveals of a window at ahigher level. This matter is morefully covered in section 2.1‘Setting-out facework’.

Once openings and perpendshave been identified and located,broken bonds may appearelsewhere. If full length bricks orthe intended bondingarrangement cannot bemaintained over the length ofthe wall then somerearrangement will be required.This may result in a new patternof cut bricks.

PARTICULAR CARE WITHBROKEN BOND

Great care must be taken inaligning the perpends of anypattern of broken bond that hasbeen formed or any otherchanges in the facework bonding(fig 2.39a). These changes attractthe eye and if they contain anymisalignment of perpends it willbe more noticeable than in thegeneral mass of brickwork suchas a flank wall (fig 2.39b).

If the discrepancy in the wall isonly slight then it may be betterto tighten or open carefully allcross joints rather than to ‘crop’bricks. If the perpends are to bealigned correctly then all cut

bricks should be exactly the samelength and the easiest way to dothis is to prepare the bricksbeforehand using a brick gaugeand if available a masonry benchsaw.

CHECKING PERPENDALIGNMENT

Once above DPC, the bricklayerneeds to plumb up and mark the

arris of every fourth or fifthbrick very lightly in pencil.Make a test with the type ofbrick in use to ensure that themarks can either be removed orwill not be visible on the finishedbrickwork. Particular care mayhave to be taken with sometextured bricks.

Checking perpends can easilybe carried out by either of thefollowing methods:

Plumb perpends

Figure 2.39a. Care taken to plumb a broken bond.

Figure 2.39b. Poor plumbing at broken bond is visually disturbing.

Plumb line

Perpends allowedto creep

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• Place the spirit level on thearris of the lower alternatecourses and transfer theirpositions up the wall(fig 2.40).

• Place a large ‘T’ squareagainst the arris of the loweralternate courses and transfertheir positions up the wall.

Perpends should be checkedconstantly, starting with thecorners. If the perpends on alarge corner are ‘allowed towander’ it may be impossible tocorrect the error in the main wallabove (fig 2.41). Racking backrequires special care becauseperpend misalignment can veryquickly occur. Also perpendmisalignment can easily occurwhen toothing is used (fig 2.42).

Toothing should be avoided asit usually results in poorly filledjoints when filling in thetoothing. This is likely to increasethe amount of water penetratingthe outer leaf and be ofparticular concern to engineers ifthe brickwork is structural. Iftoothing is unavoidable, takeparticular care when filling in.

Perpend alignment, like allbricklaying skills, requires theindividual to stand uprightoccasionally, to step back fromhis work and look at what he hasdone and consider its qualitybefore resuming work.

Figure 2.40.

Arris of brickplumbedwith level

Figure 2.41. Plumb racking brickwork withcare at corners.

Plumb bothperpends

Figure 2.42. Plumb toothedbrickwork with care at corners.

KEY POINTS

■ Consider the actions necessaryto maintain vertical perpendsbefore coming out of the groundwith facework.

■ Where more than one bricklayeris working on a line divide thewall with a tingle.

■ Check verticality at frequentintervals.

■ Take particular carewith perpends when raisingcorners.

■ Take particular care withperpends at broken bond.

Bricklayer’sline

Mark every 4thor 5th perpend

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CUTTING BRICKS 31

One of the best ways ofassessing the standard ofbricklayers is to examinethe accuracy and neatnessof their cutting of bricks.High standards dependon skill, care and attentionand the use of the correcttools and establishedtechniques.

CUTTING BRICKS –TRADITIONALLY BY HAND

Rough cuttingTrowels may be used for‘rough cutting’ but they donot give the necessary accuracyand neatness for faceworkwhich needs more appropriatetechniques and tools.

Fair cuttingFor fair cutting, bricklayers useclub hammers, bolsters, combhammers and brick gauges whichthey carry as part of their normaltool kit.

Selecting bricks for cutting withhammer and bolsterSelect evenly burnt brickswithout small fire cracks andother blemishes (fig 2.43). Thelatter tend to shatter or break inthe wrong place under theimpact from a hammer andbolster.

Frogged bricksIf frogged bricks are splay cut,the solid bed surfaces shouldbe the longer and thefrogged bed the shorter, asin figure 2.44a not figure 2.44b.The latter will be more likely tobreak during cutting and layingor fail in use.

Measurement and marking ofbricks for cuttingA simple brick gauge(fig 2.45) will aid fast, accuratemarking when many brickshave to be cut, as for instancewhen building broken bond infacework. Accurate, cleancutting will help to maintainneat and plumb perpends.The work sizes of brick batsare shown in figure 2.46.

2.5 CUTTING BRICKS

Figure 2.43. Brick with fire crack.

This portionis very weak

Figure 2.44b. An incorrectly cutfrogged brick.

158.75 mm

102.5 mm

46.25 mm

Figure 2.45. A typical brick gauge.

Figure 2.44a. A correctly cut froggedbrick.

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Bricks should be marked onthree sides, the face and oppositeside and one bed surface whichmust be the solid bed of singlefrogged bricks.

CuttingUse a small mound or thick layerof sand as a firm cutting pad. Thesand, by supporting the brickevenly, minimises the risk of thebrick breaking in the wrongplace. Alternatives to sand arepads made from DPC off-cuts orfrom sacking.

• Place the brick on sand or ona pad with the faced side ofstretcher uppermost for thefirst blow (fig 2.47).

• Turn the brick, face down, forthe second blow.

• Place the brick flat or frogdown for the last blow.

• If the strength of the blows iscorrectly adjusted, and thisonly comes with experience,

the third blow will completethe cut.

• If not, repeat the 1st, 2ndand 3rd stages until the brickbreaks cleanly.

• To achieve a straight cut onthe face side, NEVER startwith the brick flat or frogdown.

• Trim any rough edges with ascutch or comb hammer.

Cutting bricks on a scaffoldWhen bricks have to be cut ona scaffold, make an adequatespace, possibly by removing aspot board or stack of bricks.Keep the work areas clear ofbroken bricks for safe workingconditions.

Regulations regarding the handcutting of bricksIt should be noted that ‘Healthand Safety’ regulations requirethe wearing of eye protectorswhen cutting bricks with ahammer and bolster.

CUTTING BRICKS WITH AMASONRY BENCH SAW

The use of masonry bench sawsis effective and advisable whenlarge numbers or particular typesof bricks have to be cut.

Experience suggests that while3-hole perforated bricks can becut satisfactorily by hand it is verydifficult to cut multi-holeperforated bricks accurately andconsistently without creating alot of waste. Similarly, the cuttingof very high strength, low waterabsorbency solid bricks willalmost certainly require a benchsaw (fig 2.48).

Masonry bench saws areparticularly useful for cuttingbricks at an angle which can bevery difficult to do by hand. Forfurther information about benchsaws and their location (seeSection 6.9 ‘Bricklaying tools andequipment’).

Correct operation• For safety, keep area around

the bench saw free fromdebris and obstacles.

• Ensure blade is tight onspindle.

102.5 mm

158.75 mm

215 mm

102.5 mm

46.25 mm

A three-quarterbat

A quarter-bat

A standardbrick

A half-bat

65 m

m

Figure 2.46. Work sizes of brick bats.

Figure 2.47. Cutting a brick.

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KEEPING BRICKWORK CLEAN 33

• Check trolley moves freely onthe rails.

• Ensure an adequate supply ofwater in the machine.

• Clearly mark bricks to be cut,as described in ‘Measurementand marking’ in this section.

• Put on ear and eye protectorswhich are required by law butalso wear gloves, waterproofapron and boots.

• Place brick on the slidingtable and offer up so that theblade is central over thecutting mark. Secure brickwith fixing clamp.

• Turn on power to startmachine and check that theblade turns evenly and freefrom wobble.

• Offer the brick on the slidingtable to the rotating blade,apply pressure to the spring-loaded foot pedal to draw theblade down on the brick. It isimportant to ‘let the machinedo the work’. A little evenpressure, keeping the motorrevolutions even, is enoughto guide the blade throughthe brick.

• Keep fingers clear of blade,never look away whileusing saw.

• If sparks are emitted it usuallymeans insufficient water isreaching the blade.

• When the brick is almost cutthrough, release pressure

so that chipping doesnot occur.

• When cutting is complete,switch off, unclamp the brickand leave to dry before use,as, if saturated, the brickfaces may become smearedwith mortar.

• Change the water beforeeach change of brick. Light,buff bricks, for instance, maybecome stained if cut afterblack bricks.

NOTE: An approvedCautionary Notice (AbrasiveWheels Legislation) must bedisplayed for easy readingby operatives.

Figure 2.48. Bench saw.

KEY POINTS

■ Always use a pile of sand orother pad when fair cutting.

■ Prepare a space when cutting onscaffolding.

■ Use a gauge for quick, accuratemarking.

■ Apply bolster to face side first.

■ Do not strike too hard withbolster.

■ Select technique to suit type ofbrick.

■ Follow all safe workingprocedures when operating abench masonry saw.

2.6 KEEPING BRICKWORK CLEAN

Well designed, specified andotherwise skilfully built facingbrickwork can becomedisfigured by mortar stainsunless care is taken to workcleanly and protect materialsand finished work.

This section is mainly aboutgood trowel technique andcontrol of mortar consistencyto minimise such staining.

But it also refers to othertechniques, describedelsewhere in this book.

TROWEL TECHNIQUECross jointsApply mortar deftly to the end ofbricks so that faces are keptperfectly clean while filling the

cross joints completely tomaximise rain resistance(figs 2.49a & b) (see Section 6.7‘Rain resistance of cavity walls’).

Bed jointsSpread mortar fully acrossthe wall, but let none droopand stain the facework below.Do not deeply furrow(figs 2.50a & b).

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To avoid smearing the bricks inthe course below, gather thesurplus ‘squeeze’ of bed jointmortar produced as each brick is

pressed down to the line. Dothis with the trowel blade,making a ‘cutting’ action alongthe line of the bed joint,

horizontally not upwards(figs 2.51a & b).

Do not put too much beddingmortar on the wall. It willincrease the risk of wetting thebrick face and can lead toexcessive tapping whichencourages water towards theface. Estimating the correctquantity of bedding mortar andspreading it efficiently is animportant training aspect(fig 2.52).

Point the trowel along the wallwhen tapping bricks down sothat any mortar dropping fromthe blade falls on the bed(fig 2.53a). If the trowel is heldacross the wall, mortar can dropon the face (fig 2.53b). Takegreater care as you modify yourtrowel technique to reach higheras the wall rises.

MORTARSExcessively wet mortar, whethersite-mixed or delivered in tubs,retarded and ready-to-use(see Section 4.1 ‘Mortars’),is a common cause of dirtybrickwork.

In order to press bricks downby hand, bricklayers need smoothworkable mortars, but if theycontain too much water orplasticising admixtures they willbe ‘sloppy’, causing even themost skilful bricklayers to smearthe face.

Bricklayers are responsible foradjusting the consistency andworkability of mortars to suit thetype of bricks being used. Butthey must not, without thepermission of the architects orengineers, adjust the proportionsof cement, lime and sand as thiscan reduce the strength ordurability of mortars.

Figure 2.49a. Apply mortar cleanly toend of bricks.

Figure 2.50a. Acceptable lightfurrowing.

Figure 2.51a. Correct cutting action. Figure 2.51b. Incorrect cutting action.

Figure 2.50b. Unacceptable deepfurrowing reduces load-bearing capacity.

Figure 2.49b. Avoid smearing the face.

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KEEPING BRICKWORK CLEAN 35

Sand for mortarsMortars should be made fromwell-graded sand containing fine,medium and coarser particles(see Section 4.1 ‘Mortars’fig. 4.3). Well-graded sands usedin mortars help retain mixingwater long enough for themortar to develop its maximumstrength, durability and adhesion.Sand containing only largerparticles makes ‘hungry’ or‘short’ mortar, allowing mixingwater to ‘bleed out’ on the spotboard and/or down the wall face.Factory-produced mortars fromreputable suppliers can beexpected to contain suitably

graded sands. Builders’merchants usually refer to suchsands as ‘building sands’.

Lime in mortarsLime helps to prevent mortarsdrying out too rapidly while inuse. This is considered to improvecohesion, workability andadhesion and in turn reduce therisk of smearing.

TYPES OF BRICKSBricklayers are responsible foradjusting the consistency andworkability of mortars to suit thetype of bricks. (For further

information on bricks seeSection 6.10 ‘Brick manufacture’.)

Higher absorbency bricksProviding such bricks are not wetat the time the mortar is spread,they will normally have sufficientsuction rate to absorb somewater immediately, therebyreducing the risk of mortarsrunning down the facework.

But, if the bricks are extremelydry, as in a hot summer, they mayabsorb water too quickly. In thatcase it is better to reduce theirsuction rate by wetting, ratherthan making the mortar too wetand ‘sloppy’.

Figure 2.52. Judge the right quantity of bedding mortar and spread evenly.

Figure 2.53a. Mortar drops on bedof brick.

Figure 2.53b. Mortar may dropdown face.

Figure 2.54. A typically high absorptionbrick with a high suction rate when dry.

Examples of such bricksare some machine-mouldedstock and handmade bricks(fig 2.54).

Lower absorbency bricksSuch bricks generally have a lowsuction rate and absorb very littlewater from mortars as they arespread. When using such bricksbricklayers should adjust theconsistency of mortars toproduce a less ‘sloppy’ mix inorder to prevent its runningdown the face.

Examples of such bricks areextruded wire-cut bricks(fig 2.55).

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Textured bricksDragwire and other texturedbrick faces tend to pick upmortar more readily than smoothfaces during bricklaying.

To reduce this risk, remove the‘squeeze’ of excess mortar insmaller amounts by two or threehorizontal passes of the trowel asthe brick is squeezed down,rather than a single pass whichtends to pile mortar on the face.

OTHER TECHNIQUESGood trowel technique alone isnot enough. Protect bricks frombecoming very wet from rain andground water when in store and

loaded-out on the scaffolding. Ifmedium to low absorbency bricksare very wet it becomes moredifficult to avoid smears (SeeSection 1.3 ‘Handling, storageand protection of materials’).

Completed facework shouldalso be protected to prevent rainfrom washing fine particles ofcement, lime and pigments fromfresh mortar.

Plinths and other projectingbrickwork should be protectedfrom mortar droppings. Scaffoldboards next to facework shouldbe cleared of mortar and turnedback during rain, and overnight(see Sections 1.2 ‘Protection ofnewly built brickwork’ and 6.6‘Appearance’).

CONCLUSIONThe necessary cleaning down offacework at the end of acontract can be greatly reducedby good trowel technique andavoiding the use of ‘sloppy’mortars.

In addition, vulnerablefinished brickwork must beprotected from subsequentstaining by mortars andmaterials used by other trades.Mortar must be cleared fromscaffold boards and thosenearest the brickworkturned back to preventsplashing caused by rainfalling on them.

Figure 2.55. A typical low absorptionbrick with a low suction rate, especiallywhen wet.

KEY POINTS

■ Keep mortar workable but reducemixing water as much as possible.

■ Use well-graded building sand.■ Do not spread bedding mortar

too thickly.■ Remove surplus mortar from

face with horizontal cuttingaction of trowel.

■ Apply cross-joint mortarcarefully to end of bricks.

■ Do not tap bricksunnecessarily – press themdown to the line.

■ Although bricks may have to bewetted in hot dry weather donot lay bricks that are saturated.

2.7 FINISHING MORTAR JOINTS

The type of joint finish andthe skill and care with which itis carried out, profoundlyaffects both the appearanceand rain resistance ofbrickwork (see Sections 6.6‘Appearance’ and 6.7 ‘Rainresistance of cavity walls’).

Today, most brickwork is‘jointed’, which means thatthe joints are finished as the

bricklaying proceeds.‘Pointing’ of mortar jointsthat were raked out onthe day the brickworkwas built is not nowcommon. If pointing isspecified it is normallycarried out after thecompletion of bricklaying(see Section 2.8 ‘Pointing andrepointing’).

Joint finishing is usually left toa convenient moment. ‘Joint-upbefore you break for tea’ is theusual reminder from the foremanbricklayer or charge hand.Likewise, bricklaying willgenerally stop before the end ofthe day’s work to leave time forjointing-up.

This section stresses not onlythe importance of allowing

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FINISHING MORTAR JOINTS 37

sufficient time for finishingjoints correctly but the need todo so at the right timesthroughout the working day.

APPEARANCE‘Good pointing can improvepoor brickwork but badpointing can spoil goodbrickwork’, is a saying wellknown to experiencedbricklayers. Similarly, carefulfinishing of mortar jointing canminimise the effect of smalldeficiencies in bricks andbricklaying but careless jointfinishing can make them lookworse.

Jointing-up is a critical part ofbuilding facework and is notsomething to be ‘dashed off’apart from the main operation ofbricklaying. It considerably affectsthe permanent appearance offacework as almost one fifth ofthe total surface consists ofmortar joints.

Probably the most importantaspect of jointing-up is to avoidsmudging the bricks or blocks(see Section 2.6 ‘Keepingbrickwork clean’).

TIMINGTiming is probably the mostimportant aspect of jointing-up,particularly when making a neatflush joint without smudging thefacework.

The right time to joint-up isdetermined by both the suctionrate of the bricks and weatherconditions at the time the bricksare laid.

At one extreme, bricks of lowwater absorption that are verywet will have a low suction rate.The bricks will tend to ‘float’,

and the mortar will dry slowly,especially during wet or coldweather.

At the other extreme, highwater absorption bricks that arevery dry will have a high suctionrate and the mortar will dry outvery quickly, possibly before abond with the bricks has fullydeveloped.

To avoid these extremeconditions all bricks should beprotected from saturation, and inhot, dry weather the suction rateof higher absorption bricksshould be reduced by dockingor lightly spraying so that thesurface is left damp rather thanwet.

During summer months it isusually necessary to joint-upevery two or three courses in alength of walling typically builtby one bricklayer. In winter,twice only in a lift of brickworkmay be appropriate. The mortarshould be ‘soft’ enough for thejointing tool to leave a smoothsurface and to press the mortarinto contact with the brick arrisesin order to maximise rainresistance.

Trying to finish a mortar jointwhich is too dry, and pressingtoo hard with the jointer can‘blacken’ the joint face and leavea crumbly surface (fig 2.56).

Jointing-up too soon spreadsthe mortar and leaves a roughjoint surface (fig 2.57)Northamptonshire bricklayers say‘Wait until the joints have“hazelled off” a bit before youjoint-up’.

TECHNIQUEWhen ‘ironing in’ to give joints a‘bucket handle’ finish forexample, each bricklayer must

use the same diameter jointerfor consistency (fig 2.58). Thejointing tool must remain incontact with brick arises above

Figure 2.56. Jointing-up late can disturband crumble mortar surface or ‘blacken’ itby over-rubbing.

Figure 2.57. Jointing-up too early cansmear mortar and leave a rough surface.

Figure 2.58. Correct use of jointer.

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and below the bed joints andeach side of cross joints,otherwise ‘tramlines’ will be left(fig 2.59).

Cross joints must always befinished first whatever the jointfinish. The only exception to thisrule is when applying tuckpointing.

If square recessed joint finish isspecified, the use of ‘chariot’jointers (fig 2.60) or other depthgauges (fig 2.61) will help eachbricklayer to rake out to the samedepth. After raking out, therecessed mortar should normallybe ‘polished-up’, not left rough,in order to maximise the rainresistance of the joint. Use theinsert in a chariot jointer or asquare jointing tool.

If a weather struck finish isrequired, all cross joints must beinset the same side, usually theleft-hand side, by both right andleft-handed bricklayers (fig 2.62).Otherwise there will be distinctdifferences in appearance due toshadow lines.NOTE: With weather struck andcut pointing the depth of insetand ‘boldness’ of mortarprojection must be consistent.The thickness of the pointing

trowel is sufficiently bold.(see Section 2.8 ‘Pointing andrepointing’)

It may appear easy to achievea high standard of simple ‘flush’jointing but experience, care andattention is required if the jointsare to be left looking truly flush.

If finished too soon ‘wet’mortar will be smeared on theface of the bricks. If left too late,so that the mortar is too ‘dry’, itwill crumble and leave ‘misses’and an incomplete and unevenlycompacted surface.

Steel tools are used to finish thesurface of bucket handle, struckweathered and also give the finalpolish to square recessed joints.Steel tools are not used to finishflush joints as they tend to leaveconspicuous tooling marks. Apiece of hardwood, about200 mm long by 50 mm wide and10 mm thick with a half-roundedend, rather like a doctor’s spatula,is commonly used to flatten themortar joints. Great care shouldbe taken to ensure that both crossjoints and bed joints are left trulyflat and not ‘dished’.

A very light brushing willremove fine crumbs of mortar andleave a matt surface rather than apolished one as from a steel tool.

The comments on ‘brushing’, insection 2.8 ‘Pointing andrepointing’, applies equally tojointing. Generally, delay brushinguntil the end of the day in summerand leave until the next day indamp or cold winter weather.

ATTENTION TO DETAILCare is needed when finishingjoints at external angles (fig 2.63).Finishing of joints in internalangles must carefully emphasisethe tie-bricks or bonding at thesepoints, finishing alternately to leftand right (fig 2.64), not with astraight joint (fig 2.65).

Take care to continue with thejoint finishing under projectingbrick-on-edge sills, under copingsand the soffits of soldier archesover openings.

Figure 2.59. Incorrect use of jointerleaving ‘tramlines’.

Figure 2.60. Chariot jointer showingspike for raking joints to a consistentdepth.

Figure 2.61. An improvised but effectivedepth gauge.

Figure 2.62. Forming a weather struckjoint.

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POINTING AND REPOINTING 39

Immediately after a brick hasbeen laid the surplus mortar iscut flush with the face. Themain purpose of anysubsequent joint finishing is to

improve the rain resistance ofthe wall by compacting thesurface of the mortar andpressing it into close contactwith the bricks.

At vertical movement jointsin facework leave a vertical,parallel sided 10 mm space formastic sealant. Do not leavegaps at the ends of bed jointsso that the sealant spreads togive unsightly ‘mouses’ ears’(fig 2.66).

MORTARBuilding sand that ispredominantly fine grained willproduce a closer textured,smoother and denser surfacefrom the action of the jointerthan will coarser sands. Lime inbricklaying mortar tends toproduce a more compact surfacethan when air entrainingplasticisers are used.

Figure 2.63. Pay attention to externalangles.

Figure 2.64. Correctly finished internalangle.

Figure 2.65. Incorrectly finishedinternal angle.

Figure 2.66. ‘Mouses’ ears’ in a verticalmovement joint.

KEY POINTS

■ Take care to judge the besttime to joint-up.

■ All bricklayers should use thesame profile jointing tools andtechnique.

■ Take particular care at angles,sills and vertical movementjoints.

■ Use fine grained sands for finejoint finishing.

■ Brush lightly if at all.

2.8 POINTING AND REPOINTING

JOINTINGToday most face brickwork is‘jointed’ which means that thejoints are finished as the workproceeds and should require no

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further attention at the end ofthe day.

POINTINGOccasionally architects will specifythat the joints be ‘pointed’ inorder to achieve a particular effect.

When new brickwork is to bepointed, all joints are raked 12 to15 mm deep on the day the wallis built ready to receive a differentmortar at a later date (fig 2.67).

The pointing is usually adifferent colour and may berequired to have a particularprofile, e.g. flush, struckweathered, half-round tooled orsquare recessed, all of which canalso be formed as a jointingprocess as the work proceeds(fig 2.68).

In this section, only weatherstruck and cut pointing will bedescribed, as it is a commonlyused profile for pointing andrepointing (fig 2.69). Also, it is

not practicable to form theprofile as part of the jointingprocess because the bricklayers’rhythm would be disruptedwhilst they stopped to apply,to every joint, extra mortar toform the profile. Forming aweather struck and cut finish is apointing, not a jointing operation.

TOOLSPointing trowels with blades 50,75, 100 and 150 mm long areused with a hand held hawk. Theshortest trowel is known as a‘dotter’ (fig 2.70).

THE PROCESSPointing is seldom popular withbricklayers, for being a staticoperation and requiring patience,care and attention it can be acold job during the winter.

Figure 2.67. Raked out joints.

Figure 2.69. Weather struck and cutpointing.

Figure 2.68. Typicaljoint profiles exceptingstruck and cut. (See alsoinside front cover.)

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Specialist pointing gangs areusually engaged for large areasof walling.

Careless pointing can spoilgood brickwork and conversely,good pointing can considerablyimprove ‘questionable’ facework.

Before pointing begins, loosedebris should be removed fromthe joints with a dry brush andthe work ‘wetted down’ to adamp condition. Wetting downreduces the amount of watersucked from the pointing mortar

by the existing brickwork whichif too great would preventcomplete hydration resulting in aweak crumbly mortar.

Cross jointsCross joints are filled first. Thepointing mortar should be firmlypressed home and compactedwith the inset on the left-handside and the ‘cut’ on theright-hand side so that every jointlooks the same width (fig 2.71).

Both left and right-handedbricklayers must inset on the leftand cut on the right to preventthe completed wall face having apatchy appearance (fig 2.72).

The inset and cut projectionmust not be exaggerated. In bothcases 1 mm is enough.

When the cross joints arecompleted over about 1 m2 of wallsurface, the top and bottom ‘tails’of mortar should be pressed away.

Bed jointsA trowel with a longer blade isused to apply the mortar to bedjoints.

Press the pointing mortar firmlyinto the joints, insetting just 1 mmat the top and ‘cut projecting’ thelower edge by the same amount.Sloping or ‘weathered’ surfaces,by shedding rainwater morereadily, are considered to providebetter rain resistance thanrecessed or even flush joints(fig 2.73).

Bed joints are cut guided by apointing rule, a wooden straightedge with spacing blocks to holdit off the surface of thebrickwork. Joints may be cutusing the point of a towel(fig 2.74a), but some bricklayersfind that a specially made cuttingtool known as a ‘Frenchman’ ismore manageable (fig 2.74b,c).

Figure 2.70. 50, 75, 100 & 150 mm trowels.

Figure 2.71. Cross joint.

Figure 2.73. Filling bed joints.Figure 2.72. Cutting a cross joint.

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It is important to cut themortar bed joints so that they allappear to be the same width.

TimingNeither cross joints nor bed jointsshould be cut until the mortarhas stiffened a little. This willensure a clean cut. Theabsorption of the bricks andweather conditions willdetermine the timing.

Bricks with a high absorptionwill allow cutting to be carriedout sooner than bricks of lowabsorption. Similarly, cutting canbe carried out sooner in warmdrying weather than in colddamp weather.

Pointing should not be carriedout if frost is likely or after a longperiod of frost if the bricks arestill frozen.

External anglesBed joints should be neatlyformed at corners and reveals(fig 2.75).

BrushingAt the end of the day a lightbristle brush may be used toremove any crumbs of excessmortar left after cutting the

Figure 2.74a. A pointing rule and trowel in use.

Figure 2.74b. A pointing rule and Frenchman.

Figure 2.74c. A pointing rule and Frenchman in use.Figure 2.75. External angles at cornersand reveals.

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joints. Great care should betaken to avoid making brushmarks in the soft mortar. Itmay be advisable to leavebrushing the pointing whichhas been completed late in theday, until the following morning(fig 2.76).

REPOINTINGBefore old brickwork is repointedthe cause of the deteriorationshould have been established.It is usually the result of slowerosion over many years but if itis due to, say, sulfate attack onthe mortar the cause should beremedied first.

The sequence of operations forrepointing old brickwork isvirtually the same as for newwalling, except that the jointswhich may be heavily weatheredor perished must be cut out firstusing a hammer and bolster withcare in order to cause minimaldamage to the bricks. It isessential that the recess soformed be left square. The brickedges should be absolutely freeof old mortar so that the newmortar (fig 2.77) can bondeffectively with the bricks.

The recess should be no lessthan 10 mm and no more than15 mm deep. If it is too shallow

the mortar may not have asufficient bond with the bricksand if it is too deep it may bedifficult to force the mortar in forthe full depth.

At the same time lichen andmoss should be removed bycareful brushing so as not todamage the bricks.

The brickwork should then bedampened, not soaked, andwork should proceed asdescribed for pointing newbrickwork.

MORTAR MIXESPointing mortars should be ‘fatty’and cling to the trowel. This canbe achieved by the addition oflime which improves thecohesiveness of mortar, its bondwith the bricks and the rainresistance of the brickwork.

Under normal conditions ofexposure a 1:1:6cement:lime:sand mix will bespecified as appropriate. Withcalcium silicate bricks a 1:2:9 mixmay be required. With very densebricks only and in situations ofextreme exposure the mortarmay be 1:1/4:3.

In general the mortarshould be no stronger thanthat used in the constructionof the wall.

MORTAR BATCHINGWhether the cement, lime andsand are all mixed on site orcement is added to premixedlime:sand, careful measurementfor every batch is essential ifmortar colour variations andpatchy brickwork are to beavoided. It is virtually impossibleto achieve satisfactory results ifmeasurement or gauging is doneby the shovelful.

Consistent results are alsodifficult if pigments are added onsite. The use of premixedlime:sand for mortars is the onlypracticable way of producingcoloured mortars.

Figure 2.76. The result of brushing jointstoo soon.

10–15 mm

Figure 2.77. Recessing joints forpointing.

KEY POINTS

■ Remove lichen and moss fromold brickwork before repointing.

■ Ensure joints are recessed squareand all old mortar and dust isremoved before pointing orrepointing begins.

■ Dampen the wall by wettingdown and allow to drain beforestarting work.

■ Press mortar into crossjoints first, followed by thebed joints.

■ Do not exaggerate the inset orprojection of the mortar.

■ Cut joints so that all appear thesame size.

■ Do not brush the finished worktoo soon.

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The familiar brick shape hasproved to be the mostsuitable for building andmanufacture for over threethousand years, and it will bereferred to here as the‘standard’ brick.

Even so, from earliest timesspecial shapes have beenmade to fulfil functional anddecorative requirements andtoday their use has beenrevived to meet the need forattractive and enrichedbuildings. For the bricklayer,laying special shapes requirescare and attention if thearchitect’s design is to berealised in practice.

THE PURPOSE OF SPECIALSHAPES

To create shapes in brickworkwhich would be impossible,unsatisfactory or expensive usingonly ‘standard’ bricks.

DEFINITIONSBricks of special shapes and sizesSuch bricks are referred to inBritish Standards as ‘Bricksof special shapes and sizes’ ormore commonly as ‘specialshapes’ or even just ‘specials’(fig 2.78).

Standard specialsThe term ‘standard specials’refers to those shapes and sizesspecified in BS 4729(1). It doesnot imply that manufacturers orsuppliers generally hold themin stock.

Non-standard specialsThis term describes any bricks ofspecial shapes or sizes notspecified in BS 4729. They aresometimes referred to as‘purpose made specials’ or ineveryday speech as ‘specialspecials’.

AVAILABILITY AND STOCKSSome of the more commonlyused standard specials, e.g.single bullnose and cants andplinth headers and stretchers arestocked by suppliers but theywill frequently be made toorder.

Some special shapes may takelonger to produce than‘standard’ bricks because theyare formed, dried, fired andhandled by different processes

and in some cases new mouldsor extrusion dies will have to bemade. This should be taken intoaccount when programmingbrickwork requirements andplacing orders.

STORAGEAll ‘specials’ take longer toproduce and are more expensivethan ‘standard’ bricks and shouldbe carefully and systematicallystored and protected from rainin order to reduce damage andwastage and make it easier tofind particular types whenrequired.

Money spent on appropriatestorage is likely to bejustified, particularly as wasted‘specials’ can seldom be replacedquickly.

2.9 BRICKS OF SPECIAL SHAPES AND SIZES

Figure 2.78.

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BRICKS OF SPECIAL SHAPES AND SIZES 45

BASIC FUNCTIONSSpecial shaped bricks may begrouped according to their mostusual function:

• for changes of direction atangles other than 90 degreese.g. ‘squints, external andinternal angles (doglegs)’.

• for changes in thicknessvertically, e.g. ‘plinth bricks’.

• for chamfered and radiusedcorners, e.g. ‘cant andbullnose bricks’.

• to stop, neatly and effectively,the freestanding end of a runof brickwork or to changefrom one profile to another,e.g. stops for ‘standard’, cantor bullnose brick-on-edgecappings.

• to return cappings andsoldier courses neatly andeffectively.

• for bonding brickworkwithout cutting ‘standard’bricks, e.g. ‘King and Queenclosers’.

• for tightly Curved brickwork,i.e. ‘radial bricks’.

• for arches. Tapered archbricks are available forbuilding semi-circular archeswith parallel-sided jointsbetween each arch brick.

NOTES:1. Many ‘specials’, because they

have single frogs or have atexture so that the brick has a‘top and bottom’, are availablein left-hand and right-handversions, e.g. king closers,cants, bullnoses, squints,angles and certain returns.

2. Because standard and specialshape bricks are sometimesformed or fired in differentways the colour or texture mayvary slightly. If this is thought

to be unacceptable thesupplier or manufacturershould be informedimmediately and certainlybefore the bricks are walled in.

SETTING OUTSquints, external and internal(dogleg) anglesWalls which include anglebricks should be set out to theface side as with any facework.The same rules of bondingmust be applied at obtuse anglesas apply at right-angled corners(fig 2.79). The use of squints

instead of external angles givesa smaller face lap but it appearsto have proved adequate inpractice. Squints have anadvantage that being easier tomanufacture the angle is oftenmore accurate.

BS 4729(1) includes a rangeof angle bricks for internaland external angles of 30°, 45°and 60°. There is a choice ofsizes to turn the corner andmaintain bond in half lapped orquarter lapped bonding with orwithout the addition of closersor three-quarter bats.

Plinth bricksBonding should be set out sothat perpends align vertically

An external angle andcloser establish half-bond

An external angle andthree-quarter batsestablish half-bond

An internalangle (dogleg)establisheshalf-bond

A squint brickestablishes half-bond

A squint brick andcloser establishesquarter-bond

Figure 2.79. Examples of bonding of angle bricks at a quoin.

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from the base below theplinth, through the plinthcourse to the walling above(fig 2.80).

This requires pre-planning by thesupervising bricklayer before workbegins, using pencil and paper toensure that the correct quoin

bricks are used, as a mistake willbe permanent and conspicuous.

Pre-planning ensures that anybroken bonding is at or near thecorner below the plinths, then,when the plinth courses havebeen bedded, the brokenbonding at the cornerautomatically disappears.

Cant and bullnose bricksSetting out is the same as forwalls with normal bricks at thecorners but special attentionshould be paid to plumbing thecorners as indicated below.

PLUMBINGWhen plumbing single cant orbullnose bricks, simply tap thequoin headers and stretchersbackward or forward until thefaces next to the corner are trulyvertical at A and B (fig 2.81).

When plumbing squint orexternal angle quoin bricks theyshould be tapped along the lineof the wall in order to plumb thefaces, marked C and D (fig 2.82).

This skill in laying squint andexternal angle bricks needs to be

75

56 56

327

215

75

75

75

75

75

75

75

Figure 2.80. Bonding plinth bricks.

A B

Figure 2.81. Plumbingcant bricks at a quoin.

Plan first course

Plan second course

D

C

Figure 2.82. Plumbing angle bricks ata quoin.

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developed so that the angle lookstruly straight when viewed frombelow (fig 2.83).

LAYING TO LINESpecial thought must be given tofixing a line and pins when‘running-in’ a course of some‘special’ bricks (fig 2.84).

It is good practice to considerthe most obvious ‘sight line’ suchas the edge or arris of any courseof ‘specials’ which will beimmediately apparent to anyonelooking at the finished building.

HANDINGSome smooth faced specialshapes such as single cants andsingle bullnoses may be reversedwhen used for example on eitherside of an opening (fig 2.85).

This is not so with manytextured bricks which initiallylook and weather differently iflaid ‘upside down’ (fig 2.86). Forthese, separate right and lefthanded versions must be orderedand stored carefully for easy andobvious identification, butreference should always be made

Figure 2.83. A well plumbedsplayed quoin using textured andhanded, squint bricks.

Figure 2.84. Fixing line and pins whenrunning a saddle back coping.

Figure 2.85. Smooth cant bricksmay be reversible.

Figure 2.86. Textured cant bricksmust be handed.

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to BS 4729(1) to check the correctversion before placing an order.

External plinth returns areanother example where left andright handed versions arerequired (fig 2.87).

Right and left handed versionsof single frogged specials maybe specified for reveals toopenings where they have to belaid frog uppermost in order toresist heavy loads from a lintelabove. Alternatively, if theappearance of the special allowsit to be laid either way up thefrogs may be filled with mortarand allowed to set before it islaid frog down in the work.

Some manufacturers stamp‘LH’ or ‘RH’ as appropriate tohelp identification.

HOW TO IDENTIFY WHICHHAND – LEFT OR RIGHT?

The following method toidentify left and right handversions of specials is used inBS 4729(1).

When the special is placed onits normal bed surface and itsequivalent stretcher face viewed,if the modification of the shape isto or at the left hand end of thebrick it is a left hand brick. If it isto or at the right hand end it is aright version.

Do not identify right or lefthand by brick’s intended positionin the work.

STOP BRICKSThese provide a transition from aspecial shape to a ‘standard’brick (e.g. fig 2.88a). Left andright hand versions will berequired for some stop bricks(e.g. fig 2.88b).

STOP ENDSLarge bullnose and cant bricks(215 � 215 mm or 215 �159 mm) stop straight runs ofcant or bullnose bricks on edgeeffectively and securely (fig 2.89).

RETURN BRICKSThese allow a special shapeto be returned at rightangles neatly and securely(fig 2.90).

Lefthand

Righthand

Figure 2.87. External plinth returnsmust be handed.

Figure 2.88a. Doublebullnose stop.

Figure 2.88b. Singlebullnose stop (left hand).

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BONDING BRICKSOne of the essential skills of abricklayer is the efficient use ofhammer and bolster in cuttingbats and closers from wholebricks for bonding purposes.However, in order to save timeand wastage where largenumbers of these are required itis usually possible to obtain themspecially made (fig 2.91).

ARCH AND RADIAL BRICKSThe use of these specials forbuilding arches and curvedbrickwork is covered insections 5.3, 5.4 and 5.7.

Reference(1) BS 4729:2005 ‘Recommendations

for dimensions of bricks (includingthose of special shape)’.

Figure 2.89. Stop endto double bullnose.

Figure 2.90. Single cant return. Figure 2.91. Queen closer.

KEY POINTS

■ Check if any ‘specials’ arehanded.

■ Check whether purpose-madebats and closers are availableon site.

■ Protect all specials fromdamage and waste. They maybe difficult to replace.

■ Take particular care to plumbsquint and angle bricks.

■ Maintain perpends of facebrickwork through plinthcourses.

■ Consider the ‘sight line’ whenlaying a course of projecting‘specials’ to the line.

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3 GOOD PRACTICEThis section deals with someaspects of the work that are notstrictly concerned with themanipulative skills involved inthe craft, nonetheless they needto be understood andimplemented to achieve good

results – working in hot andcold conditions, blendingbricks to achieve uniformity ofcolour.

This section also deals with somespecific constructions and

highlights the inclusionof accessories andcomponents generallyincorporated into modembrickwork – ties, insulation,DPCs, pipework, manholecovers, etc.

3.1 AVOIDING DAMAGE FROM EXTREMES OF TEMPERATURE

This section is concernedprimarily with the preventionof frost damage to brickwork,but makes reference topreventing damage duringhot, dry weather.

Preparations for winterbuilding should be made wellin advance and equipmentand materials procured readyfor use.

MORTARS AND FROST DAMAGECements set more slowly atlower temperatures. If mortarsfreeze before the set is complete,their ultimate adhesion, strengthand durability will be reduced

and the brickwork may have tobe rebuilt (fig 3.1).

Avoiding frost damage to mortarsPreventing stocks of sand andlime:sand from becoming wet willprevent ice forming within them.

Simply cover them withwaterproof, preferably insulated,sheets supported by a lightframework arranged to maintainan air space immediately over thestock pile.

Heating of aggregates, bricksand blocks, as has beenrecommended in the past, doesnot appear to have provedpracticable.

Tubs of retarded mortar shouldbe covered to prevent the mortarfreezing.

Bricklaying should stop whenthe air temperature is at or below3°C and falling (fig 3.2)

Figure 3.1. The result of frost damageto unset mortar.

Figure 3.2. Checking the air temperature from a convenientlyplaced thermometer.

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AVOIDING DAMAGE FROM EXTREMES OF TEMPERATURE 51

as recommended in the MasonryCode of Practice(1).

Bricklaying should resume onlywhen the air temperaturereaches 1°C and is still rising –but only if the bricks are notfrozen. To test, brush cold wateron to the faces of some of thebricks with a paint brush; if thebricks are frozen the water willturn to ice.

A more direct method uses a‘spear’ thermometer to check thetemperature of a trial mortar bedleft to cool for a suitable time(fig 3.3).

Brickwork can be protectedfrom wind by heavy gauge,reinforced polythene sheetingsecured to the scaffolding.Alternatively, work areas and

materials can be enclosed inheated lightweight structures(fig 3.4).

If frost is likely before themortar has set, the brickworkshould be protected bywaterproof insulation (seeSection 1.2 ‘Protection of newlybuilt brickwork’).

Protection from frost should beleft in place for about 7 days. Ifthere is any doubt about thecondition of the mortar, heatselected small areas to abovefreezing point. If the mortar isfound to be soft, it has not set,and the brickwork may have tobe rebuilt.

Take care not to stain thebrickwork. A radiant heater maybe suitable.

‘Anti-freeze’ agentsAccelerators, althoughsuccessfully used in concrete, arenot recommended for masonrymortars. This is because theadditional heat liberated fromthe accelerated hydration ofsmall amounts of cement willbe quickly conducted away bythe bricks and blocks whichhave a relatively high thermalcapacity.

Admixtures containingcalcium chloride should never beused as they may lead todampness and corrosion ofembedded metals like wall tiesand reinforcement.

As there is no UK experience ofadmixtures which reduce thefreezing point of mortars beingmixed, they are notrecommended. Some mayadversely affect the hydration ofcements.

The frost resistance of mortarsduring the setting can beimproved by adding air-entraining admixtures to the mix.However, their use may reduceboth the mortar strength andadhesion and should be addedonly with the permission of thearchitect or engineer. Theyshould comply with BS 4887-1and the manufacturer’sinstructions should be strictlyfollowed.

Ready-mixed lime:sand formortars and ready-to-useretarded mortars supplied to sitesmay contain the optimumquantity of air-entrainingadmixture. Unauthorised extraadmixtures should not be added.

Protecting bricks from frostModerately frost resistant (M)clay bricks are at risk from frostattack when saturated and

Figure 3.3. A spearthermometer in use.

Figure 3.4. External and internal views of a temporary enclosure.

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52 GOOD PRACTICE

should be protected, whether inthe packs, stacked on thescaffolding or in the wall(see Section 6.2 ‘Frost attackand frost resistance’). But evenfrost resistant (F) bricks shouldbe protected from saturationas, if the water contentfreezes, the bricks will beunusable until they thaw.

Protection of the mixing areaThe temperature in the area ofthe mixing plant and materialsmay be kept higher and workingconditions made morecomfortable by the erection ofsimple wind screens.

BRICKLAYING IN WARMDRYING WEATHER

Bricks of high water absorptionusually have a high suctionrate. They rapidly absorbmoisture from mortars whichnot only reduces theirworkability but may seriouslyreduce adhesion.

Mortar should be laid inshort lengths to limit the lossof water before the bricks arelaid.

It is considered that the useof lime in mortars helps toimprove their bond with claybricks that have a high waterabsorption (see Section 4.1‘Mortars’).

Newly built brickwork shouldbe protected from drying outtoo rapidly as this may result ina reduction in strength(see Section 1.2 ‘Protection ofnewly built brickwork’).

Clay bricksAdhesion of mortars tohighly porous clay bricks mayalso be improved by ‘docking’

them, but they must not beoverwetted as this may lead to‘floating’ on the mortar bedand to efflorescence and stainingof the facework. Bricks of lowwater absorption should not bewetted.

Calcium silicate bricksEasier laying and betteradhesion is achieved byadjusting the consistency ofthe mortar or briefly docking,not soaking, the bricks justbefore laying.

WEATHER FORECASTSFROM THE METEOROLOGICAL

OFFICEThere are a number offorecast services available forbuilders via fax, phone or theInternet.

Fax – MetFAX is a premiumrate fax service, giving fiveday regional weatherforecasts. An indexpage listing the areas andfax numbers can be

obtained by dialling 09060100 400.Phone – MetCALL DIRECTgives you the opportunity tospeak directly to a forecasterday or night. To access thisservice call 08700 767 828.Payment is by credit cardon-line. For more details on pastweather information for planning,contract disputes and projectoverruns call 08709 0000 100.Internet – a complete rangeof forecast services isavailable on MetWEB atwww.metoffice.gov.uk. Tosubscribe or to obtainfurther information call 087090000 100.

Full details of The Met.Office’s services tobuilders can be found on theirFREE index card which you canget by calling their helpline on08709 0000 100 or by e-mail:[email protected].

References(1) BS 5628-3:2001, A4.2.3.8 ‘Mixing in

cold weather’.

KEY POINTS

■ Anticipate and prepare for coldweather.

■ Cements set more slowly in coldweather.

■ Brickwork may need rebuilding ifmortars are frozen before the setis complete.

■ ‘Anti-freeze’ admixtures areof little value in masonrymortars.

■ Never use calcium chloride.

■ High absorption clay bricks mayneed docking in hot, dryweather.

■ With calcium silicate bricks,preferably adjust the mortarconsistency.

■ Ensure that a robust, reliablethermometer is available on site.

■ Use a weather prediction serviceto anticipate need forprecautions.

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BLENDING FACING BRICKS ON SITE 53

Packs of facing bricks areblended or mixed as they areloaded-out to bricklayers inorder to minimise the effect ofslight but inevitable variationsin colour and size on theappearance of finishedbrickwork.

THE CAUSES OF COLOUR ANDSIZE VARIATIONS –

MANUFACTURING CONTROLS

Variations in raw materialsBricks are made mainly fromnatural materials deposited atdifferent times over millions ofyears, often in layers having verydifferent physical qualities.

Clay deposits vary considerablyhaving been formed by theweathering of rocks; thedepositing of sediments by riversand lakes and finally bygeological upheavals and furtherweathering.

Winning, processing and formingclayAlthough, during the winningand stockpiling of clay, thevarious materials are mixed ashomogeneously as is practicable(fig 3.5), slight variations persist,particularly between stockpilesproduced at different times.

Raw materials from stockpilesare crushed and finely groundand other materials may beadded. The final mixture may bemoulded or pressed or extrudedand wire-cut to shape beforebeing dried ready for firing (seeSection 6.10 ‘Brick manufacture’).

Firing clay bricksModern tunnel kilns arecontinuously monitored andcontrolled to minimise differencesin firing temperatures from onepart of a kiln to another, andfrom time to time (fig 3.6).Even so, some slight variationswill remain, particularlybetween the top and bottom ofa kiln. Larger variations occurwith some other methods offiring e.g. in clamps andintermittent kilns.

Calcium silicate (sandlime andflintlime) and concrete bricksCalcium silicate bricks consist ofaggregates, lime and pigmentsprocessed in high pressure steamautoclaves. Concrete bricks

consist of aggregates, cement andpigments cured similarly to otherconcrete products. Both types ofbricks can vary in colour and sizeand although the same principlesfor blending apply as for claybricks it is advisable to follow themanufacturer’s particularrecommendations in this regard.

Control of variationsDuring all manufacturingprocesses, the use of modern andtraditional skills, sophisticated plantand quality control techniquesminimise variations in colour anddimensional tolerances. The risk ofthese variations adversely affectingthe appearance of finishedbrickwork can be minimised bysupervisors, bricklayers and

3.2 BLENDING FACING BRICKS ON SITE

Figure 3.5. Stratifiedquarry face andstockpiles layered forweathering.

Figure 3.6. Computermanaged kiln control.

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54 GOOD PRACTICE

labourers following therecommendations in this section.

THE NEED FOR SITE BLENDINGVariant bricks within a load can,if grouped together, result inunacceptable colour patches,patterns or bands in brickwork(figs 3.7, 3.8).

Blending disperses the fewvariants among the many typicalbricks to achieve brickwork freeof patches.

The need to blend bricks thatare intended to be uniform incolour (e.g. smooth red bricks) isgenerally and readily understood,but it is not always understoodthat it is absolutely essential toblend multicoloured bricks toavoid unwanted patterns causedby bricks of one particular colourbeing grouped together (seeSection 6.6 ‘Appearance’).

Because variations in rawmaterials and firing of clay brickscan result in variations of size aswell as colour, blending of brickswill also help bricklayers tomaintain regular widths of crossjoints when setting-out facework(see Sections 6.5 ‘Allowing forvariations in brick sizes’, and 2.1‘Setting-out facework – stretcherhalf-bond’).

There is likely to be greatervariation between different loadsthan within a single load. Theblending techniques describedin this section apply to the lattercase. Minimising the adverseeffects of variations betweenloads should be tackled bythose who specify and orderbricks. They should, as soon aspossible, alert the manufacturersto the need to supply bricks of auniform appearance over a longperiod of time. It is not realistic to

expect manufacturers toanticipate this.

Modern methods of handling andtransporting bricksIn the past, bricks wereinevitably blended when theywere handled, six or eight times,from kiln to stockpiles; fromstockpiles to lorries; from lorriesto site stacks and finally loaded-out for the bricklayers. Thesefour processes were akin toshuffling a pack of playing cards(fig 3.9).

Today, bricks from kilns areformed into strapped packs ofsome four hundred and movedmechanically to site stacks on theground, loading platforms onfloors of buildings. Unless packsare blended as they are loaded-out to bricklayers there is a risk ofsimilar coloured bricks beinggrouped in the wall causingpatchy brickwork. Blending alsomixes bricks having different sizetolerances, helping bricklayers tomaintain greater regularity ofcross joints when setting outfacework (see Section 2.1‘Setting-out facework – stretcherhalf-bond’).

Figure 3.7. Failure to blend loads whenloading out.

Figure 3.8. Failure to ensure uniformitybetween loads.

Figure 3.9. The need for site blending.

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BLENDING FACING BRICKS ON SITE 55

THE TECHNIQUES OFBLENDING ON SITE

Bricks should be loaded-outpreferably from four or fivepacks but from an absoluteminimum of three. It is usuallyadvisable to draw from packs invertical rather than horizontalslices as the position of bricks inpacks tends to reflect theirposition in the kiln (fig 3.10).This is particularly true of tunnelkilns (see Section 6.6‘Appearance’).

If in doubt ask themanufacturers for theiradvice.

If bricklaying gangsunderstand the reasons for

loading-out in this way thereshould be no problems of colourpatches or banding whenworking the first lift.

However, to service bricklayerson upper lifts of scaffolding,loading bays need to be largeenough for at least three or fourpacks. If loading bays are notlarge enough some difficulty maybe experienced in avoiding colourbanding.

Loading bays up to about 7 mhigh must have hingedbaffler/guard rails for access byfork lift truck or conveyor.

Above 7 m, packs of bricks canbe lowered directly on loadingbays by tower cranes.

An alternative method is toload barrows from a number ofpacks at ground level andtransport them vertically by hoistor conveyor, but special care mustbe taken not to chip the brickswhen handling them in this way.

Blending on site alone is noteffective in eliminating colourvariations between loadsdelivered to a site over a longperiod of time. The manufacturershould be warned prior to workcommencing. It is important that,if practicable, blending takesplace between loads of bricks, aswell as between packs, especiallyif loads are from differentmanufacturing batches.

Protect tops of stacksfrom rain – secureprotection from beingblown away

Remove bandingto a safe place



Remove bricksin vertical slicesfor best blend

Figure 3.10. Loading-out from a number of packs.

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56 GOOD PRACTICE

BLENDING IN FACTORIESSome manufacturers are able toblend some bricks in the factorybefore dispatch, but furtherblending on site will usually beadvisable. Manufacturers shouldbe consulted.

SOME OTHER ASPECTSAlthough handmade/soft-mudfacing bricks have two usablefaces, the overall colour may bedifferent on opposite faces.

Moulded bricks should be laidso that they smile (see Section6.6 ‘Appearance’).

Extruded wire-cut bricks oftenhave a directional texture suchthat they should be laid in thesame orientation, i.e. ‘the rightway up’.

But, blending of bricks will beto little avail if a consistentmortar colour is not achieved(see Sections 1.2 ‘Protection ofnewly built brickwork’, 1.3‘Handling, storage and

protection of materials’, 4.1‘Mortars’, 6.6 ‘Appearance’).

KEY POINTS

■ Consult brickmakers about theirrecommendations for siteblending.

■ Explain to bricklayers andlabourers the reasons forblending, before they beginwork on site.

■ Ensure that scaffold loading baysare large enough and strongenough to carry a sufficientnumber of packs.

■ Check loads when delivered tosite and when broken down for

loading-out so that problems canbe identified before the bricksare walled.

■ Constantly check that hodcarriers are drawing verticalslices preferably from five packswhen loading-out.

■ Look out constantly fornoticeable patches or bandsof colour variation atbricklaying level and remedyimmediately whilst mortaris green.

similarly reduced hard labour butfacilitates the reduction ofwastage from breakages andchipping.

But these modern methodshave increased the need fordeliberate on-site blending ifcolour patches and banding arenot to leave permanent scars asevidence of a lack ofunderstanding or care andattention by all concerned.

CONCLUSIONModern methods ofmanufacture, handling,packaging and particularly thevirtual elimination of laborioushand loading has helped tominimise rising costs. Mechanicalhandling on site has not only

3.3 EXTERNAL CAVITY WALLS

There is more to buildingmodern cavity walls thanbedding bricks in mortar(Table 3.1).

Simple cavity walls beganto supersede solid walls (fig 3.11a) over seventy yearsago because they were morerain resistant. This superioritydepends increasingly oncareful, detailed design,specification and workmanshipas cavity walls become morecomplex to meet more exactingrequirements (fig 3.11b).

Users grow less tolerant ofrain penetration; lightlyloaded cavity walls requiremore provision to preventcracking by movement thando solid walls restrained byroof and floor loads; thedurability of wall ties hasproved critical in maintainingstructural stability; finally,cavity insulation has beenwidely adopted. Care andattention, based on anunderstanding of the waycavity walls both succeed and

fail, will minimise expensiveand disruptive maintenanceand repairs.

THE SCOPE OF THIS SECTIONThis section describes brickworkoperations, e.g. ‘12. Building-inties’, and which functionalrequirements, they mainly affect,e.g. ‘Rain resistance’. See table3.1. Reference is madethroughout to detaileddescriptions in other sections.

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EXTERNAL CAVITY WALLS 57

1. CHECKING MATERIALS ONDELIVERY

Check that all deliveries arecomplete and undamaged beforeaccepting them. In particularcheck that:

• Facing bricks are as specified;minor surface blemishes areacceptable (see Section 1.1‘References and samplepanels’); bricks have beengauged and selected for close

One brick thickwall in Flemishbond

Lintel

Double hungsash windowin brickworkrebated reveal

Double hungsash window

Stone sub-sill

Figure 3.11(a). A typical external traditional solid wall.

Block inner leafHalf-brick outerleaf

Cavity insulation

Steel lintel

Cavity tray

Stop-end tocavity tray

Vertical DPClapped behindcavity tray andin front of sillDPCResidual airspace

Insulationretaining clip

Weep hole

Windowframe withcavity closerbehind

Structuralcavity

Wall ties

UndersillDPC

Figure 3.11(b). A typical external modern cavity wall.

Figure 3.12. Butterfly, double triangleand vertical twist ties.

tolerances, if so specified, foruse e.g. in narrow piers,cappings, soldier coursesand similar features. Thewrong bricks can resultin patchiness andirregular brickworkfeatures.

• Concrete blocks are ofthe specified type andthickness. The wrongblocks may haveinadequate strength orthermal insulation.

• Wall ties (fig 3.12) are ofthe specified type andlength; plastic debondingsleeves are included ifrequired for some ties toallow movement; suitableclips are provided for tiesretaining cavity insulation.The wrong ties can result inunstable walls, cracking,misplaced insulation andrain penetration.

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58 GOOD PRACTICE

• Mortar materials e.g.cement, lime, sand, pre-mixedcoarse stuff and ready-to-useretarded mortars are asspecified; they are fromconstant sources if for use infacework. The wrongmaterials can lead toweakened and less durablemortars, variations inmortar colour and patchylooking brickwork.

• DPCs are of the specifiedtype and width; theappropriate adhesives areincluded for sealing laps atjoints; that any preformedunits have the rightdimensions. The wrongDPCs may be too narrowto be built-in effectively orhave inadequate bondwith mortar. The wrongadhesives may result ininadequate sealing at laps,allowing rain penetration.

• Cavity insulation materialsare of the correct type, sizeand thickness. The wrongmaterials can lead toinadequate thermalinsulation and rainpenetration.

2. HANDLING, STORING ANDPROTECTING MATERIALS

Handle, store and protect allmaterials to avoid damage byimpact, abrasion, excessiveloads, rain, ground water, heat,cold and contamination byother materials. Damagedbricks and mortar materialscan spoil the appearance ofbrickwork as well as reducingits strength and durability.Damaged insulation andDPCs can lead to rainpenetration and reducedthermal insulation. Damagedlintels and ties can result in

weakened walls (see Section1.3 ‘Handling, storage andprotection of materials’).

Load-out bricks preferablyfrom five packs to avoid colourpatchiness or banding ofbrickwork (see Section 3.2‘Blending facing bricks on site’).

3. SETTING-OUT ANDBUILDING FACEWORK

Set-out facework dry at groundlevel. Agree with supervisor thepositions of openings and anybroken or reverse bond;establish and maintainperpends; use gauge rods forregular coursing. Facingbrickwork of distinction isachieved by carefulpreparation before a brick islaid and the continuingexercise of basic bricklayingskills with care and attention(see Sections 2.1 to 2.9).

TABLE 3.1 Functional requirements of cavity walls

Strength/stability Rain Appearance Movement Durability Thermal resistance insulation

1. Checking materials • • • • • •2. Handle, store, protect • • • • • •3. Set-out and build facework •4. Cleanliness, protection • • •5. Mortar mixing • • • •6. Forming cavities •7. Building blockwork • • •8. Raising two leaves • (and safety)9. Jointing • • • •

10. Parapet walls • • • • • •11. Fixing window frames • •12. Building-in ties • • • •13. Building-in DPCs • • • • • •14. Building-in insulation • •15. Movement joints • • • •16. Support systems • • • •17. Lintels •

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4. CLEANLINESS ANDPROTECTION OF FACEWORK

Keep facework free from mortarsmears and splashes; protectprojecting features such asplinths and string courses frommortar droppings; protect bricksills, reveals and soffits from

mechanical damage; turn backscaffold boards nearest tofacework if rain is likely; protectnewly built brickwork from rainand frost, particularly overnight.Finished brickwork can bepermanently scarred bycarelessness and if not

protected from damage bysubsequent buildingoperations and the weather(see Sections 1.2 ‘Protection ofnewly built brickwork’; 2.6‘Keeping brickwork clean’).

5. BATCHING AND MIXINGMORTAR

Batch mortar materialsaccurately, and be aware thatdifferent mixes may be specifiedfor particular locations, e.g.below DPC level, in parapetwalls, copings, cappings, bricksills and inner leaves.

When site-mixing mortars usea method recommended inSection 4.1. Incorrectly batchedor mixed mortars can mar theappearance of brickwork andreduce its strength, durabilityand resistance to cracking(see Sections 4.1 ‘Mortars’; 6.2‘Frost attack and frost resistance’;6.3 ‘Sulfate attack on mortars’;6.4 ‘Durability of brickwork’;6.6 ‘Appearance’).

6. FORMING CAVITIESObservance of the goodpractice points noted in fig3.13 will minimise the risk ofrain penetration and costlyremedial work.

7. BLOCKWORK INNERLEAVES

Do not mix bricks and blocks ordifferent blocks in the inner leaf.This can reduce wall strengthand thermal insulation andcause pattern staining.

Chases for services should notexceed the dimensions shown infig 3.14. Sloping chases are notrecommended because the

With partial-fill cavityinsulation – arecommendedminimum 50 mmresidual air space

Clean excess mortarfrom cavity side ofboth leaves, especiallywhen building-in full-fill insulation

Avoid protrusions incavity. Snappedheaders, if required,should be purpose-made or accuratelyand cleanly cut

Immediately aboveDPC trays leave crossjoints open as weepholes at not morethan 1 m centres butwith at least twoabove any opening.Keep them clear ofdebris. Fit filtrationplugs if required

Minimum 150 mmbetween DPC andground level

Weep holes everyfourth cross joint

With full-fill or nocavity insulation – aminimum 50 mmcavity betweenleaves

Suspend lath tominimise mortarfalling down cavity.Remove and cleanafter six courses.‘Ropes’ of twistedhessian, about 3 mlong, may bepositioned abovetrays and, periodi-cally, carefullydrawn out throughcoring holes

Clear mortardroppings from tiesand cavity traysdaily. Do not damage trays

Step cavity tray upto inner leaf atleast 150 mm

Minimum 150 mmbetween DPC andbottom of cavity

Leave shallow spaceat ground level forunavoidable mortardroppings

Figure 3.13. Some points forcare when building cavitywalls.

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60 GOOD PRACTICE

difficulty of establishing theirpositions in finished walls can behazardous for users makingfixings. If in doubt ask. Theindiscriminate cutting ofchases can seriously weakenmasonry walls.

Internal leaves are generallybonded to internal walls forstability. But check the detaileddrawings; special provision maybe required to accommodatemovement and control shrinkagecracking (see Section 6.11‘Building blockwork inner leaves,walls and partitions’).

8. DIFFERENCE IN HEIGHTWHEN RAISING TWO LEAVES

(fig 3.15)Both leaves should be raised inone operation. At no timeshould the difference in heightbe more than six courses ofblockwork (approximately1350 mm) except when usingvertical twist ties when thedifference should be no morethan two block courses(approximately 450 mm)(see Table 3.2). Unsupported,newly-built single leaves areliable to be blown over instrong winds.

These recommendationsmay be discounted when thesite supervising engineer makesallowance for the reducedstability of the single inner leafin resisting wind load (e.g. byproviding temporary support orshelter) and special two-part ties(fig 3.16) are specified toovercome misalignment of bedjoints and the potential dangercaused by the sharp ends of tiesprojecting from the inner leafwhile the outer leaf awaitscompletion.

VERTICAL CHASES

HORIZONTAL CHASES

CHASES INHOLLOW ANDCELLULARBLOCKS

T

T

Maximum T13

Maximum T1 6

Minimum15 mm

NOTE: Sloping chases, although subject tothe same limitations, are not recommendedas their position is difficult to determine byusers making fixings.

Figure 3.14. Maximum depth ofchases in block inner leaves.

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9. FORMING AND FINISHINGMORTAR JOINTS

Fill all bed and cross joints solidly(fig 3.17). Partial filling,particularly of cross-joints, isone of the main causes ofincreased rain penetrationthrough the outer leaf (seeSection 6.7 ‘Rain resistance ofcavity walls’). Deep furrowingof bed joints reduces the load-bearing capacity of brickworkand blockwork leaves.

Unless otherwise instructed,iron all joints externally inthe brick outer leaf, e.g. as‘struck’ or ‘bucket handle’.

When usingbutterfly typeties and doubletriangle type(not type 2).

When usingvertical twisttype ties.

max

. diff

eren

ce 1

350

mm m

ax. d

iffer

ence

450

mm

Figure 3.16. Two-part stainless steel tie (a) and shown inposition (b). Image kindly supplied by Ancon CCL.

Figure 3.15. Maximum differences in height when raising twoleaves.

TABLE 3.2 Maximum differences in height of both leaves of a cavitywall during construction

Type of tie Maximum difference in height of the two leaves

Shape name Type no. to Block courses mm approx.to BS EN 845-1(1) DD 140 Pt 2(2)

Butterfly 4, 5 & 6 6 courses 1350 mmDouble triangle 2 6 courses 1350 mmVertical twist 1 2 courses 450 mm

NOTE: Unsupported, newly-built single leaves are liable to be blown over in strongwinds. The more onerous limitations on differences in height when using ‘vertical twistties’ is to minimise discrepancies between the level of bed joints between each leaf. Suchdiscrepancies may cause bricklayers to force the free ends of ties, built into the higherleaf, up or down to suit the level of joints in the rising second leaf. This may disrupt thebed joints and masonry units as the ties are too stiff to bend. In addition, the exposedends of vertical twist ties can cause injuries to the body and particularly the eyes.

(a)

(b)

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62 GOOD PRACTICE

This increases the rainresistance of the brickwork.

Do not recess joints inbrickwork that may becomeexcessively wet. This can leadto increased rainpenetration of the outerleaf and possible frostdamage.

The jointing techniques ofall bricklayers on a job shouldbe co-ordinated. This isessential in order tomaintain a uniformappearance (see Sections 2.7‘Finishing mortar joints’and 2.8 ‘Pointing andrepointing’).

Clean excess mortar fromthe back of the outer leaf asthe work proceeds. Excessmortar protruding fromthe joints can cause rainpenetration throughthe horizontal jointsbetween full-fill cavitybatts (fig 3.18) (see Section4.4 ‘Insulated cavity walls’).

10. PARAPET WALLSPay special attention to building-in DPC trays and flashings andDPCs under copings andcappings (fig 3.19).

Parapets are the mostexposed parts of cavity wallsand failures can result in rainpenetration, staining and

deterioration (see Section 5.2‘Cavity parapet walls’).

11. OPENINGS FOR WINDOWAND DOOR FRAMES

Fix built-in frames with approvedcramps, plugs and fixings. Do notuse timber plugs which can rot inouter leaves. Position and fixDPCs as described under ‘13.Building-in DPCs’.

Some types of proprietarycavity closers are permitted bybuilding control authorities.Check if in doubt.

12. BUILDING-IN TIESBuild-in the type and length ofcavity wall ties specified, not less

Figure 3.17. Cross joints. Solid are rainresistant – tipped and tailed are not.

Figure 3.18. Mortar joint not cut flushleads to rain penetration.

PC concretecoping

Clean mortardroppings fromtray

Weep holes atminimum of1 m centres

Carry insulationup to undersideof cavity tray

Minimum150 mm

Rooffinish

DPC bedded onfresh mortar

Rigid support

Figure 3.19. A typical cavity parapet wall.

H6469-Ch03 9/15/05 1:10 PM Page 62


than 50 mm into each leaf, andnot sloping down to the innerleaf. Position any drip in thecentre of the cavity. Maintain thespecified spacings, takingparticular care to increase thenumber of ties at openings andmovement joints (fig 3.20). Keepall ties free of mortar droppings.Ties that are merely pushed intobed joints have little pull-outstrength.

Special ties, intended torestrain movement in onedirection but allow it in another,must be built-in with care and anunderstanding of how they work.

The correct ties properlybuilt-in are essential to givethe cavity wall sufficientstrength and stability,maximum rain resistance,support and restraint to anycavity thermal insulation andto minimise the risk ofcracking (see Sections 4.2 ‘Tiesin cavity walls’, 4.4 ‘Insulatedcavity walls’ and 4.5 ‘Verticalmovement joints’).

13. BUILDING-IN DPCS(see Section 4.3 ‘Damp-proofcourses’.) Bed only specified DPCs,preferably in a single length, onfresh mortar. Lap unavoidablejoints by a minimum of 100 mm.Bond laps in cavity trays with anadhesive recommended by themanufacturer. Lapping withoutbonding is acceptable onlyagainst rising damp e.g. inground-level DPCs.

DPCS immediately above ground-levelBed DPCs on fresh mortar at least150 mm above ground or pavinglevel. This minimises the risk ofrain splashing up from hardsurfaces and of top soil beingplaced above the DPC.

Do not allow DPCs to projectinto the cavity. They form ledgeson which mortar accumulatesand bridges the cavity.

Project DPCs by 5 mm from orkeep flush with the facework.Mortar and bricks can spall asDPCs positioned behind the

face and pointed over,compress under load.

If two courses of DPC bricks arespecified they must be bedded ina designation (i) e.g. 1:1/4:3mortar to resist rising damp.

Vertical DPCsAt openings, build-in vertical DPCsto protect door and windowframes from brickwork that maybecome wet. Project the DPCsbeyond the cavity closer and intothe cavity by at least 25 mm butpreferably 50 mm. If preformedcavity closers are specified, takecare at the junction with DPCs.

Lap vertical DPCs behind DPCtrays at lintel level and in front ofDPCs at sill level. Any joints mustbe lapped and sealed (fig 3.21).This will shed water drainingdown the inner face of theouter leaf to the outer facethrough weep holes rather thaninto the cavities and insulation.

Cavity traysProject cavity trays 5 mm or keepflush with the outer face. Stepthem up at least 150 mm; buildinto the inner leaf and fix stopends. Clear mortar droppingsfrom cavity trays, taking care notto damage them (fig 3.21).Cavity trays are intended tocollect water from the cavityand drain it to the outsidethrough weep holes. Gaps,perforations or lack ofeffective stop ends can allowwater to reach lintels, framesand thermal insulation.

DPCs under copings and cappingsAt the top of cavity parapet wallsbed DPCs on a rigid bridge overthe cavity and bed copings orcappings on the DPC in oneoperation to maximise the bond

Vertical spacingof ties at jambsevery blockcourse or every4th brickcourse (if bothleaves are ofbrickwork)

Maximum450 mm

Maximum 900 mm

Maximum 255 mmfrom jamb

Maximum 255 mmfrom jamb

NOTE: If one leaf is less than90 mm thick the maximumhorizontal spacing is 450 mm.

Extra ties at jambs of openings

Figure 3.20. Cavity wall tie spacing.

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64 GOOD PRACTICE

cavity and fit close together withno mortar droppings betweenthem; cut neat slits wherenecessary to fit batts over ties.Fix partial-fill cavity insulationwith special ties, normally backto the inner leaf, leaving thespecified residual air spacebehind the outer leaf. Protectthe top of cavity insulation frommortar droppings (fig 3.22).Incorrectly fitted insulationor mortar droppingsbetween batts or slabs canlead to rain penetration andreduced insulation values(see Section 4.4 ‘Insulatedcavity walls’).

15. MOVEMENT JOINTSKeep vertical movement jointsclear of mortar, use the specifiedfiller, usually flexible cellularpolyethylene, cellular

polyurethane or foam rubber butnever hemp, fibre board orcork which are insufficientlycompressible for joints inclay brickwork which expands.Apply the specified sealant tothe correct depth in accordancewith the manufacturer’sinstructions (fig 3.23). Build-inextra wall ties at movement jointsas specified (see Sections 4.5‘Vertical movement joints’; 4.7‘Brickwork on metal supportsystems’).

Extra movement joints will berequired in parapet walls.

16. BUILDING CAVITY WALLSON METAL SUPPORT SYSTEMS

Build with special care thosecavity walls in which the outerleaf is supported on metal anglesor brackets (fig 3.24). Provide a

Weep hole

Stop end

VerticalDPC

between the DPC and the mortarbed below. Project DPCs 5 mmfrom each face of the wall. Jointsmust be lapped and sealed.

Failure of these DPCs canlead to the saturation,staining and frost failure ofthe bricks and mortar and thedislodgement of the coping orcapping (see Sections 5.1‘Copings and cappings’; 5.2‘Cavity parapet walls’).

DPCs under sillsBuild-in DPCs under sills that arenot impervious to water or arejointed. Turn them up at the backif the sill is in contact with anypart of the inner leaf.

These DPCs are to preventwater, that permeatesthrough a sill or betweenjoints which eventually crack,from saturating the brickworkbelow or being transferred tothe inner leaf.

14. BUILDING-IN CAVITYINSULATION

Build-in full-fill batts supportedon wall ties; batts should fill the

Figure 3.21. Cavity trays, vertical andsill DPCs.

Figure 3.22. Protect cavity insulation frommortar droppings.

H6469-Ch03 9/15/05 1:10 PM Page 64


horizontal movement jointbetween the underside of thesupport and the top of anybrickwork leaf immediatelybelow; tie the top of the panelsback to the structural frame asspecified or recommended by themanufacturer of the supportsystem. At least two-thirds of the

thickness of the brick outer leafshould bear on the supportingsystem. Pay particular attentionto the building-in of DPC trays.Failure to followrecommendations can resultin reduced strength andstability, rain penetrationand a poor appearance

(see Section 4.7 ‘Brickwork onmetal support systems’).

17. LINTELSBuild-in lintels with adequatebearings as specified orrecommended by themanufacturer but never less than100 mm. Bed them on mortar onfull blocks, not short lengths ofcut blocks (see Section 6.11‘Blockwork inner leaves, wallsand partitions’).

References(1) BS EN 845-1: 2001 ‘Specification

for ancilliary components forMasonry Part 1’.

(2) DD 140-2:1987 ‘Recommendationsfor design of wall ties.’

Further readingBRE Defect Action Sheet (Design).DAS 12. December 1982 ‘Cavity traysin external walls: preventing waterpenetration.’BRE Defect Action Sheet (Site).DAS 17. February 1983 ‘Externalmasonry walls insulated with mineralfibre cavity-width batts.’BRE Defect Action Sheet (Site).DAS 116. June 1988 ‘External masonrycavity walls: wall ties – installation.BS 8000-3:1989. ‘Workmanship onbuilding sites – Code of practice formasonry’.Brick Development Association: GoodPractice Note 1. ‘Cavity insulated walls.’

Sealant

No adhesion

Filler or backingmaterial

Adhesion

Figure 3.23. Filling, backing and sealing movement joints.

Stainless steel angle

Pistolbricks

Vertical cast-intoothed channels

Thermalinsulation

Figure 3.24. A typical continuous angle support system.(To aid clarity a cavity tray has not been shown)

KEY POINTS

■ In all matters described in thissection take particular care withcavity walls which will beexposed to considerable wettingfrom wind-driven rain.

■ Check correctness and conditionof all materials and componentson delivery.

■ Handle and store all materialsand components to avoiddamage and deterioration.

■ Raise both leaves together,keeping differences in height torecommendations.

■ Build-in all DPCs asrecommended with great care.

■ Take particular care with DPCsand flashings in cavity parapetwalls.

■ Maintain specified cavity widths.■ Clean excess mortar from cavity

faces.■ Avoid protrusions in cavities

from cut bricks and DPCs.

■ Minimise mortar droppings incavities.

■ Clear mortar droppings fromties, cavity trays and bottom ofcavities daily, avoiding damageto cavity trays.

■ Build-in only specified wall ties,correctly positioned and spaced.

■ Build-in ties solidly by 50 mminto each leaf, level or slopingdown to outer leaf, drips incentre of cavity pointing down.

■ Build-in various types of bricksand blocks only in positionsspecified.

■ Cut chases in inner leaf only asinstructed or torecommendations.

■ Leave open cross joints for weepholes as specified and keepclear.

■ Build-in thermal insulation asrecommended with great care toavoid causing rain penetration.

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66 GOOD PRACTICE

A frog is a depression formedin a bed face of a brick.

Most bricklayers will havebeen instructed at some timethat bricks must be laid withfrogs up and filled withmortar. At other times theymay have been advised thatbricks may be laid either way.

Both the instructions andthe advice can be correctdepending on circumstances.This section, by describinghow the performance ofbrickwork is affected by layingbricks with frogs up and down,provides an understandingof the reasons behind anarchitect’s or engineer’sinstructions. It begins withsome background informationand concludes with commentson training practice.

WHY SOME BRICKS CONTAINFROGS

For hundreds of years bricks madeby hand and moulded by machinefrom soft clays have containedfrogs, formed by inserts in themoulds, primarily to facilitatefilling the moulds and demouldingthe ‘green’ bricks (fig 3.25).

Today, a large number of bricksare made from relatively drygranular clay by the semi-drypressing process, using very greatpressure. The process is facilitatedby an insert in the mould whichforms the frog (fig 3.26).

Bricks may have frogs in one orboth bed faces, the lattergenerally being referred to as adouble-frogged brick, in whichcase one frog is usually largerthan the other.

The shape, size and number offrogs, if any, is mainly dependenton the characteristics of the clay.

FROGS UP OR DOWN? – THEEFFECT ON BRICKWORK

PERFORMANCEIn considering the effect on theperformance of brickwork thecritical factor is not whetherbricks are laid with the frogs upor down but whether the frogs,or the larger, in the case ofdouble frogs, are filled solidly ornot.

It is possible, although timeconsuming, to lay bricks withfrogs down and filled (fig 3.27),but it is only practicable withlimited numbers. For instance, ifhanded cant bricks are notavailable for either side of anopening it is possible to invertthose on one side (fig 3.28). But

3.4 FROG UP OR FROG DOWN?

Figure 3.25.

Figure 3.26.

Figure 3.27. Laying frog down and filled in exceptional circumstances.

Load trowel withsufficient mortarto fill frog

Lower brick andtrowel intoposition

Withdraw troweland bed brick inplace

H6469-Ch03 9/15/05 1:10 PM Page 66

FROG UP OR FROG DOWN? 67

this may not be visuallyacceptable with some texturedbricks (see Section 2.9 ‘Bricksof special shapes and sizes’,fig 2.86 and text). If it provesdifficult to ‘wipe’ mortar intothe frog the alternativemethod described above shouldbe used.

A number of relevantfunctions are described belowtogether with the effect oflaying the bricks with frogs upand down.

Strength and stabilityCompressive strength tests onindividual bricks generally requirethe frogs to be filled unlessstated otherwise. Engineers usethese results when calculatingthe loads that brickwork cansupport. Bricks without filledfrogs will fail at much lowerloads, as will the brickwork (fig3.29). One manufacturer statesthe compressive strength of hisbricks to be 21 N/mm2 frog upand 7 N/mm2 frog down.

If bricks are not laid frog upand filled as instructed, thebrickwork will not have the

strength intended by theengineer and may crack, spall oreven collapse. Examples ofbrickwork that must be designedand built to support heavy loadsare walls, columns and piersunder the bearings of concreteor steel beams and possiblylintels (figs 3.30 & 3.31).Padstones are usually built-in toprevent the edges of bricks

spalling when subjected toconcentrated loads from widespanning and deflecting beams.

Walls supporting concretefloors, especially in multi-storeybuildings, will almost certainly berequired to be laid frog (or largerfrog) up.

Bricks in most housing and non-load-bearing walls in framedbuildings are likely to have a

Figure 3.28. Cant brick inverted if‘handed’ versions not available.

LOAD LOAD

Load evenly distributedthroughout wall bymortar in frogs

Load concentratedat edges by lack ofmortar in frogs

Figure 3.29. Frog up is stronger.

Figure 3.30. High stresses in brickwork under beam bearings.

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68 GOOD PRACTICE

compressive strength much greaterthan that required, even when laidfrog down, but instructions maystill be given to lay bricks with frogup for other reasons, such asimproved sound insulation.

Sound insulationEffective sound insulationbetween adjacent buildings androoms within a building dependslargely on the density of the wallbetween them. Heavier wallscontribute to better soundinsulation and this may be agood reason for building themwith the frogs up and filledsolidly with mortar.

Fixings to brick wallsSmaller fixings such as thosesecured by plastic plugs or rubberbushes are generally satisfactorywhether the frogs are filled ornot. Larger expansive bolts mustbe used with care so as not todisrupt the brickwork whether ornot the frogs are filled.

Other considerationsIt is sometimes argued that theair pockets in unfilled frogsimprove the thermal insulation ofa wall. In practice the differenceis negligible and may be ignored.

A BRS Digest written in 1954stated that there was nosignificant difference in the rainresistance of a solid brick wallwhether the bricks were laid frogup or down. The BrickDevelopment Association is notaware of any subsequentevidence which contradicts thesefindings.

Some manufacturers ofhandmade bricks recommendlaying them frog up, so that the

surface creases ‘smile’, helping toshed water and improve thedurability of the bricks.

TRAINING PRACTICESSome tutors insist that trainees,when laying bricks frog-up, fillthe frogs prior to spreading themortar bed because at first theyhave difficulty in putting downenough mortar and keeping togauge. Other tutors prefer toteach from the beginning thattrainees put down enoughmortar to fill the frog and lay afull bed in one action as theymust do in practice.

AUTHORITATIVE GUIDANCEBricklayers and supervisors shouldbe aware of authoritativeguidance available on mattersrelated to their craft. In the eventof a dispute over workmanshipsuch guidance is likely to betaken into account. Somerelevant guidance is quotedbelow.

Bricklayers bear theresponsibility for buildingbrickwork to achieve thedesigners’ aims. Failure to doso will result in poorperformance and thepossibility of expensiveremedial work.

Figure 3.31. High stresses in brickwork under lintel bearings.

KEY POINTS

■ Always lay bricks frog up if soinstructed.

■ If no Instructions are given –ask.

■ If there is no one to giveinstructions – lay frog up,especially under heavy loads.

H6469-Ch03 9/15/05 1:10 PM Page 68

MANHOLES AND INSPECTION CHAMBERS 69

Brickwork in manholes andinspection chambers will beout of sight after backfilling,but must be built with care asfaults can make effectivemaintenance difficult and areusually expensive to repair. Ifchambers leak excessivelyduring water pressure teststhey will have to be repairedor even rebuilt.

This section provides abasic guide only. Practice mayvary in different parts of thecountry being usuallydetermined by local buildingcontrol officers.

FUNCTIONS ANDREQUIREMENTS

Covered inspection chambersand manholes are built over

drains and sewers to allow easyaccess for inspection, testing,maintenance and cleaning.A manhole is an inspectionchamber within which aperson can work.

All chambers should be:

• big enough to allow for theconnection of branch drainsto a main drain

• virtually watertight• able to carry all expected

vertical and lateral loads

Recommendations fordesign, specification andconstruction are given in BS5628(1), BS EN 752(2).

NOTE: The depth of a chamber istaken from the top surface of thecover to the invert level of the

downstream end of the channel(fig 3.34).

MINIMUM DIMENSIONS OFCHAMBERS

Based on the recommendationsof BS EN 752(2).

Chambers without branches(fig 3.32)

The recommendedminimum internal dimensionsare:

• 450 mm long by 450 mmwide, if not more than 1 mdeep (fig 3.32a)

• 1200 mm long by 750 mmwide, if more than 1 m deep(fig 3.32b).

‘Laying bricks with frogs. Unlessotherwise advised, by singlefrog bricks with frog uppermostand bricks with a double frogwith deeper frog uppermost.Fill all frogs with mortarwhere specified. COMMENTARY –Brick walls built with frogsdown and unfilled are weakerand less resistant to soundtransmission. Advice should besought as to whether bricks laidfrog down are acceptable. It isnot intended that the voids inperforated bricks are filledwith mortar. Clause A.5.1.3.3 BS8000-3: 2001 Annex A to BS5628-3: 2001.

‘Filling of joints and frogs.Single-frogged bricks shall belaid frog uppermost anddouble-frogged bricks shall belaid with the deeper froguppermost. All frogs shallbe filled with mortar’.Clause 2.4.3, SP 56 1988‘Model specification forclay and calcium silicatestructural brickwork’.Published by British CeramicResearch Ltd.

‘Frog up or frog down’? Bricksmust be laid frog up with alljoints filled when maximum

strength or weight is required forthe brickwork. When neither isthe prime requirement, thebricks may be laid frog down.If separating walls are requiredto meet Building Regulationsfor sound insulation, bricksshould be laid frog up to givemaximum weight’. ‘Oxfordclay fletton range technicalinformation on brickwork’.London Brick 1987.

3.5 MANHOLES AND INSPECTION CHAMBERS

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70 GOOD PRACTICE

Chambers with branches(fig 3.33)Length. A minimum of 300 mmis allowed for each nominal 100or 150 mm branch at the sidehaving most connections. Anadditional allowance, usually of

600 mm, is made at thedownstream end from the lowestbranch, to allow for a connectionto the channel junction and forrodding.Width. The minimum widthshould be 150 mm, or the main

nominal pipe size, if it is larger,plus 150 mm for a side with nobranches plus 300 mm for a sidewith branches, BUT, note thatthe total width must be not lessthan 750 mm if the chamber ismore than 1 m deep.

Minimum nominal dimensions ofchamber covers• 450 mm by 450 mm for

chambers not more than 1 mdeep and

• 600 mm by 600 mm forchambers more than 1 mdeep (fig 3.32).

BASE SLABSBase slabs must be designed andbuilt to support the brickworkand vehicular traffic. Slabs willnormally be 150 mm thick,although 100 mm may bepermitted in domestic workwhere there is no risk of vehiculartraffic loads.

Bases need not project beyondthe external face of brickwork.The concrete mix will normally begrade C20P or a standard mix toBS 8500(3). If you are site-batching by volume, ask forguidance on proportions ofcement and aggregates to beused (fig 3.34).

WALLSBricks It is good practice tospecify a Class B Engineeringbrick for walls in drainage work.However, if the drain is carryingchemically aggressive fluids it ispossible that Class A will bespecified. If in doubt ask thesupplier or manufacturer (seeSection 6.4 ‘Durability ofbrickwork’ table 6.4 masonrycondition ‘L’).

450 min.

450

min

.

Plan

Vertical section

1200 min.

750

min

.

Cover600 × 600mm

Plan

Vertical section

150

150

300

100 or 150 mm branches

Direction of flow

Channel pipe

Channel junctions

Benching

Plan

600 mmi.e. 300 mmper branch

600 mmfrom lowestbranch

+

Minimum 750 mm if chamber ismore than 1 m deep

Figure 3.32a. Chambers1 m or less deep.

Figure 3.32b. Chambers more than 1 m deep.

Figure 3.33. Basic minimum dimensions for chambers with branches.

Figure 3.32. Minimum dimensions for chambers without branches.

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Mortar Mortar should bedesignation M12 i.e. 1:1/4:3cement:lime:sand. Ensure thatmortar is accurately batched andproperly mixed otherwise it maysuffer sulfate attack. Somespecifiers may require you to usesulfate-resisting cement withF2 and F1 quality clay bricks or if

the ground contains sulfates(see Section 6.4 ‘Durability ofBrickwork’ table 6.5, masonrycondition ‘L’).

Brickwork Walls will normally beone brick thick to resist groundand water pressures. Half-brickthick walls may be permitted if

the brickwork is above the watertable, the chamber is not morethan 900 mm deep and will notbe subject to vehicular traffic.

One-brick walls are normallybuilt in English bond, but if theground water pressure is high,‘water or manhole’ bond may bespecified to give increasedresistance to water penetration(fig 3.35).

BENCHINGBenching is the raised concretesurface between channels andwalls (fig 3.34). It must slopesufficiently to direct overflowingsewage back into the channelsbut be flat enough to provide asafe foothold when roddinginside a manhole. The absoluteminimum slope is 1:12, but alittle steeper is preferable.

COVER SLABSConcrete cover slabs used to roofmanholes are generally 150 mmthick, and must be designed andbuilt to carry all loads includingtraffic. They should never be lessthan 100 mm thick in order toprovide sufficient cover forreinforcement (fig 3.34).

They are often set well belowfinished ground level to allowaccess covers and frames to bebedded to a road camber or toallow future alterations ofground level without disturbingthe slab.

METHOD OF CONSTRUCTION

Support of trenchesPeople die in quite shallowtrenches that collapse withoutwarning. Unless the sides are

Manhole coverand frame

Brick levelling courses

Concrete cover slab

Manhole walling one-brick thick

Benching minimum fall 1:12

25 mm radius

Channel pipe

Concrete base slab

Dep

th o

fch

ambe

r600

150

150

750

1700

Figure 3.34. Section through typical manhole looking up stream.

1. Outer leaf built in stretcher half-bond

2. Outer leaf rendered

3. Inner leaf built with bed and cross joints staggered against wet renderingCross joints

staggered

Bed jointsstaggered

150

Concrete base slab

Figure 3.35. Water or manhole bond.

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72 GOOD PRACTICE

battered to the angle of repose,ensure that suitable support isprovided for all trenches 1.2 m ormore deep and for shallowertrenches in which you or otherswill have to work substantiallybelow ground level. The angle ofrepose depends on the type andcondition of the ground, so if indoubt seek advice from asupervisor.

Loading-out work areaBecause the face side is internal,it is easier to work from theinside of manholes, standingastride the channel. Load outbricks around the four sides withlow stacks because the trenchsides may be unstable. Onemortar spot board is normallyadequate.

Levelling from datum (fig 3.36)Level across from the datum pegor paving. Gauge down to theconcrete base, marking on thegauge rod:

• Thickness of cover and frameplus bedding mortar

• Levelling courses• Cover slab or start of

corbelling• Remaining courses of

brickwork.

Setting out• Spread a thin skim of mortar

on the concrete base(fig 3.37).

• Mark position of internal wallface in the mortar, adjustingthe dimensions to avoidbroken bond.

• Set out the first course dry,normally in English bond, tominimise the number of cutbricks, especially if very hardbricks are to be used.

• You may be told on siteto build toothed quoins(fig 3.38), in order to avoidcutting queen closers fromvery hard bricks, particularlyif a bench saw is not availableat that time. This methodcannot be used if thechamber is to be renderedexternally. Furthermore, greatcare should be taken to avoiddislodging the projecting and

therefore vulnerable cornerbricks either before or duringbackfilling.

Building the walls, pipework,benching and step irons(fig 3.39)• Bed the first course of bricks

to establish the bond.• Solidly bed connecting pipes

and build-in as the brickworkproceeds.

Drain pipe

Concrete base

Fall

Channel

Remaining depthdivided into suitablebrick courses

Thickness of coverand frame

Datum peg set at heightof manhole cover.

Gauge rod

Cover slab

Levelling course

Figure 3.36. Gauging down from a datum peg.

Fall

Mark position ofinternal wall facein mortar

Skim of mortaron concrete base

Figure 3.37. Setting out the internal wall face.

H6469-Ch03 9/15/05 1:10 PM Page 72


• Lay bricks with single frogs orthe larger of double frogsuppermost.

• Many specifiers will requirenominal 10 mm bed andcross joints as recommendedfor brickwork in general in BS5628(1) or specifically, forchambers, by the WaterResearch Centre(4). Somespecifiers may follow therecommendations in BS EN752 that joints should be notmore than 6 mm and not lessthan 4 mm thick.

• Take particular care to fill alljoints solidly across the wallwidth. If chambers, whentested, lose more water thanis permitted, the leaks aremost often through badlyfilled joints and so thebricklayers are to blame.

• Although ‘full and flushjoints’ are often specified,BDA recommends that jointsare ‘tooled’ on both sides ofthe brickwork in order tomaximise water resistance,particularly if the ground

water level might rise abovethe bottom of the chamber.

• After a couple of courses,stand on a plywood off-cutresting on dry bricks. This willbe easier on the feet and willprotect the channels andpipes from accidentaldamage.

• Raise about 6 courses,keeping internal cornersplumb. Check for squareinside the chamber as soonas the brickwork rises abovethe pipes.

• Form the benching at thispoint as the higher thebrickwork the more difficult itbecomes. Rough-out shape ofbenching in solidly beddedbrickwork or using a stiffconcrete mix, as describedunder ‘Base slabs’.

• Rise vertically from the edgeof the channel forming a25 mm radius and slope upto the walls at not less than1:12, but remember that itmust be possible for othersin the future to stand on thebenching comfortably andsafely whilst working in thechamber (fig 3.39). Usuallythe final 25 mm of benchingis finished with a 1:3cement:sand render appliedand trowelled smooth whilethe concrete is still green.

• Replace plywood whenbenching is hard, to protect itand the channels.

• Pipes of 300 mm or more indiameter should be protectedeither by a one-brick relievingarch turned over the pipe forthe full thickness of the wallor a reinforced concrete lintel(fig 3.40).

• Build in step irons everyfourth course into the wall

Normal English bondwith queen closers

Use of whole bricks toform toothed quoin

Figure 3.38. Alternative method of forming a quoin, compared with the normal method.

Benching minimum1:12 slope down tochannel

25 mmradius

Channel

Line ofinternal wall face

One brick thickEnglish bond. All bedand cross joints filledsolidly with 1:1/4:3cement:lime:sandmortar

Figure 3.39. Brickwork and benching.

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74 GOOD PRACTICE

beneath the opening inthe cover slab as illustrated(figs 3.41 & 3.42).

• Continue brickwork plumbto the level of the undersideof the concrete cover slab,which is usually 300–400 mmbelow ground level. Shutterand cast in-situ concrete coverslab with reinforcement asdetailed and specified.

• Alternatively, corbel outin headers in order to reduce

the plan size of themanhole to the size of thecover. Corbelling should notexceed 30 mm in each course.

• The access cover is positionedat the downstream end tofacilitate rodding upstream(fig 3.41).

Bedding cover frames (fig 3.42)• Raise levelling courses to

bring the frame and coverup to the required level.

• Solidly bed the frame in1:3 cement:sand mortarwith the cover in place toprevent the frametwisting. Take care toget the top surface exactlylevel with adjacentpaving, datum peg orto suit the road camber.

• Remove cover and neatlypoint up around inside offrame.

• Replace cover and form filletaround frame to protectexposed edge.

References(1) BS 5628-3:2001 ‘Code of practice

for use of masonry, materials andcomponents, design andworkmanship’.

(2) BS EN 752-1/2/3/4 ‘Drainageand sewer systems outsidebuildings’.

(3) BS 8500-1:2002 BS 8500-2:2002Complimentary Standards to BS EN206-1 ‘Concrete: methods forspecifying concrete’.

(4) ‘Sewers for adoption – design andconstruction guide for developers’.Water Research Centre (1989) plcfor the Water AuthoritiesAssociation.

Figure 3.42. Section AA through manhole lookingdownstream showing positions of step irons.

Brick-on-edge relieving arch Concrete lintel

NOTE: For clarity no concretebenching is shown

Figure 3.40. Methods of protecting large pipes of 300 mm and more.

Opening inconcreteroof slab

Wall under roofslab

Direction offlow in channel

Step irons

A A

300

Metal cover inframe bedded onbrickwork

Header levellingcourses

Roof slab

Step irons

750

max

imum

300

300 300

450

max

imum

Figure 3.41. Plan showing position of cover opening and step iron.

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KEY POINTS

■ Ensure trench sides are safe – asksupervisor if in doubt.

■ Gauge down from datum pegmarking position of access coverand frame, levelling courses andcover slab on a guage rod.

■ Mark internal size of chamberon base slab.

■ Load out with low stacks ofbricks around excavation.

■ Set out brickwork bond tominimise cutting – especially ifhard bricks are specified.

■ Fill all bed and cross jointssolidly.

■ ‘Tool’ joints internally andexternally.

■ Check internal corners for plumband square after raising aboutsix courses.

■ Slope benching down to channelat least 1:12 but not too steep.

■ Replace plywood working panelto protect benching andchannels.

■ Position correct access cover andany step irons at downstream end.

■ Bed cover frame solidly, point upinternally and form filletexternally.

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The variety of componentsalready introduced in theforegoing sections as typicalexamples are dealt with here ingreater detail. The section alsoincludes articles on aspects ofconstruction that are frequently

encountered in modernconstruction and involve morecomplex construction detail thantraditional work – buildingbrickwork on metal supportsystems as cladding for framedstructures, reinforcement in

masonry structures. Theincorporation of movementjoints into brickwork is alsodetailed; this is an aspect ofmodern work that is frequentlymisunderstood and incorrectlyassembled.

4 ACCESSORIES

4.1 MORTARS

Mortar is a mixture ofmaterials used in bedding,jointing and pointing bricksand blocks in masonry walling(fig 4.1).

Mortar consists of sand; abinder, usually ordinaryPortland cement (OPC); waterand frequently a plasticiser.Hydraulic lime, commonlyused as a binder at one time,is rarely used today in normalbuilding work, but it isregularly used for therestoration and repair of oldbrickwork.

When hydraulic limemortar is specified itscomposition requiresparticular care. Allowancefor longer setting timesshould also be made.

THE IMPORTANCE OFWORKMANSHIP

Good designers specifythe right mortar forstrong, durable, rainresistant, crack free andattractive brickwork.

BUTThey rely on the care and skill ofwell-informed bricklaying teamsto achieve these ends.

WHAT IS REQUIRED OFMORTAR?

WorkabilityBricklayers require a ‘fatty’ mortarwhich hangs on the trowelwithout being sticky, spreadseasily and stiffens neither tooquickly nor too slowly (fig 4.2).

BUTIn achieving workability,bricklayers must also producea mortar to meet the life-longrequirements of brickwork.

Life-long requirements include:• adequate compressive strength• adequate bond strength

between mortar and bricks• durability – i.e. resistance to

frost and chemical attack• joints sealed against wind-

driven rain• a pleasing appearance.

Figure 4.1. Spreading mortar. Figure 4.2. A ‘workable’ mortar.

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MORTARS 77

The ability of mortars to meetthese requirements depends on:

• THE MATERIALS SPECIFIED –by the designers and

• THE WORKMANSHIP – of thebricklaying team, includingthe protection of materialsand brickwork against badweather conditions.

MATERIALSAs delivered for on-sitebatching.Architects, engineers or surveyorsare responsible for specifying theright type and quality of materials.The bricklaying team is responsiblefor storing, protecting,proportioning, mixing and usingthem with care.

SandSands for bricklaying mortarsare normally dug from a pit.Sea sands contain salts whichadversely affect the quality ofthe mortar. They should not beused unless they have beenwashed and supplied by areputable firm.

Good mortar sands are wellgraded having fine, medium andcoarser particles.

Poorly graded sands, withsingle size aggregates, contain agreater volume of air and requiremore binder to fill the spacesand make the mortar workable

(fig 4.3). Mortar made frompoorly graded sands will beweaker, unlikely to retain fineparticles and more likely toshrink, leaving cracks for rain topenetrate.

• Use only the specified sand.Different sands may requiredifferent mix proportions.

• Obtain all the sand for the jobfrom one source. Differentsands can result in differentmortar colours and patchybrickwork.

• Store and protect sand fromrain and contamination byother building materials,mud, vehicles and plant.Dirty sands produce weaker,less durable and discolouredmortars.

CementThe most commonly used binderin bricklaying mortars is ordinaryPortland cement (OPC). ‘Masonrycement’ is frequently used butremember it contains only 75%OPC, the remainder being aninert filler, which has no bindingcapability.

• Use only the specifiedcement.

• Obtain all the cement for thejob from one source. Differentcements can result in differentmortar colours and patchybrickwork.

• Never use high aluminacement.

• Never substitute masonrycement for Portland cement.Different mix proportions willhave to be used and there willbe a change of colour.

• Store bags off the ground andprotect from rain (fig 4.4).

• Do not use cement which hasbeen exposed and contains‘lumps’. It will produceweaker and less durablemortars.

Hydrated limesIn the 19th and early 20thcenturies, hydraulic limes wereused as the only binding agentin mortars. Even if these werestill generally available theywould not be practical for themajority of modern buildingas they harden slowly ratherthan set quickly as cementmortars do.

Today hydrated, non-hydrauliclimes in powder form are oftenadded to Portland cement-basedmortar to improve workability.Being water retentive, lime alsoimproves the bond with thebricks and therefore thebrickwork’s tensile strength andrain resistance.

Poorlygraded

Wellgraded

Figure 4.3. Simplified diagrams of sand grading. Figure 4.4. Protect cement bags.

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78 ACCESSORIES

PlasticisersCement, sand and water aloneoften produce harsh mortarswhich are difficult to use. Theirworkability can be improved byadding lime or proprietaryplasticisers which entrain (trap)minute bubbles of air in themortar.

• Use only proprietary plasticisersas specified or permitted.

• Follow the manufacturers’recommendations regardingquantities and mixing timesprecisely.

• Never use domestic orcommercial detergents as theymay contain harmfulchemicals. Unlike proprietaryplasticisers, they generateuncontrolled quantities of largeair bubbles producing weaker,less durable mortars (fig 4.5).

‘dry’ ready-mixed lime:sand(‘coarse stuff’) or ‘wet’ready-to-use retardedcement mortars.

WATER• Water used for mixing should

be clean enough to drink.

Ready-mixed lime:sand formortars• Properly proportioned and

mixed lime:sand formortars is delivered ‘dry’ inbulk to sites by specialistsuppliers. The mixes mayalso include plasticisers andpigments. Ready mixedlime:sand is convenient touse but must be treated withcare.

• Protect from contaminationby other materials, mud andvehicles (fig 4.6).

• Protect from extremes ofweather. Fine particles oflime and pigments can bewashed away by rain orblown away by drying windscausing variations in mortarcolour.

Ready-to-use retarded mortarsThese mortars are delivered‘wet’ to site usually in coveredcontainers of 0.25 or 1 m3

capacity (fig 4.7). They can beused without further additions ormixing for up to thirty six hoursi.e. two working days. It is goodpractice to:

• Cover containers to minimisethe effects of weather, preventcontamination by vandalismand accidents to children.Some containers are made sothat they may be padlocked.

• Clean containers beforerefilling to avoid contaminationof fresh mortar and renewplastic liners if provided.

• Avoid re-tempering the mortaronce the initial set has begun.If in doubt consult the supplier.

Describing mortar mixesMortars are specified as:

• proportions of specificmaterials, e.g. 1:1:6cement:lime:sand or

• by a ‘designation’ number,(i), (ii), (iii) or (iv). This permits

Figure 4.5. Detergents make poor mortar. Figure 4.6. Container in use with top cover removed.

PigmentsPigments are added to produce‘coloured’ mortars.

• It is virtually impossible to addaccurate proportions on siteand maintain colourconsistency.

• Pigmented mortars areusually delivered to site as

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MORTARS 79

the use of one of threemortar types and these are tobe made with one of fourbinder mixes. These are setout in table 4.1 which isbased on information taken

from the Masonry Code ofPractice(1) with the addition of‘General-purpose mortars’which are mortars made withcement, lime and sand withair-entrainment.

• General-Purpose Mortars,developed in the 1990sat BRE, combine lime andair-entrainment withPortland cement-basedmortars. This enhances theiradhesion, workability anddurability making them lesssusceptible to variations insand grading and therebysimplifies the mixspecification.

WORKMANSHIP(3)

GaugingAccurate gauging (measurement)of the quantities of mortaringredients before mixing isessential if the required mortarstrength, durability andconsistency of colour is to beachieved.

Figure 4.7. Delivery ofready-to-use retardedmortars.

TABLE 4.1 Mortar mixes

Basic Cement:lime:sand Cement:sand Cement:lime:composition with air-entrainment with air-entrainment sand

Binders Ordinary Portland Masonry cement Masonry cement Ordinary Portland cement cement or sulfate- with high lime with other than orresisting Portland content high lime content sulfate-resisting Portland cement (1:1 OPC:lime) cement

Designation

BS 5628 BS EN 998-2:2003

(i) M12 1:0–1/4:3(ii) M6 1:1/2:4 1/2 � Air 1:3 1:2 1/2–31/2 1:3–4 � Air 1:1/2:4–4 1/2(iii) M4 1:1:5 1/2 � Air 1:4 1/2 1:4–5 1:5–6 � Air 1:1:5–6(iv) M2 1:5 1/2–6 1/2 1:7–8 � Air 1:2:8–9

– Mortar of high durability – General use mortar of good durability

NOTES:The types of mortars of any one designation are of approximately equal strength. The range of sand proportions is to allow forvarying grades of sand. The second quantity e.g. 1:1:5–6 for designation (iii) is for a well-graded sand. Smaller proportions of sand(or large proportions of cement and lime) are necessary with less well-graded sands (see fig 4.3).The proportions of hydrated limes may be increased by up to 50% to improve workability.With the permission of the designer, plasticisers may be added to lime:sand mixes to improve their early frost resistance. Ready-mixedlime:sand mixes may contain such admixtures. This table is based on information given in Table 14 of BS 5628-3:2001.

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80 ACCESSORIES

Weigh batching is the mostaccurate method but isseldom used, except on largesites, for practical or economicreasons. Measurement byvolume, if done with care,is generally adequate.Site batching – all ingredientsmixed on site.

If hand mixing:• Use accurate and consistent

proportions of materialsother-wise the mortar andbrickwork may not besufficiently strong or durableand the colour will certainlyvary.

• The use of shovels toproportion the materialsis totally unsatisfactory.A shovelful of damp sandhas a greater volume thana shovelful of dry powderycement (fig 4.8).

• Mortars batched this wayoften contain too littlecement and this is thecause of a large proportionof brickwork failuresinvestigated by BDAand BRE.

• Proportioning is best doneby using bottomless steelor timber gauge boxes on a

flat clean mixing surfaceor alternatively 10 litresteel buckets. A separatecontainer should be usedfor cement.

• Mix all the ingredients dry by‘turning’ the heap threetimes.

• Hollow the centre and addthe water, gradually mixing itwith the mortar.

• Finally ‘turn’ twice for acomplete mix and to improveworkability.

• If using hydrated lime thebest results are obtainedby mixing it with sandbefore adding water. Allowthe resulting ‘coarse stuff’to stand for at leastsixteen hours (overnight).Gauge with cementimmediately before use.‘Coarse stuff’ need notbe used immediately butshould be protected fromdrying out.

If machine mixing:• The first two points, under

‘hand mixing’ above,concerning batching, and thelast point on hydrated limesapply equally to machinemixing.

• Clean the mixer thoroughlyafter use especially ifpigments have been used.

• Use the correct amounts ofwater. Too much will produceweak mortar and may lightenthe colour. An estimation ofthe amount of water requiredmay be determined fromtable 4.2.

Various experienced bodiesadvocate slightly different mixingsequences. However, there isagreement that it is unsatisfactoryto add the cement, lime and sandto the mixer and mix them beforeadding the water. Tests haveshown that much of the cement isleft clinging to the side ofthe mixer drum, leading tocement-lean mortars.

Two advocated methods arenoted below:

The first is based on therecommendations in the BritishStandard Code of Practice for‘Workmanship on building sites’(3)

• Load three-quarters of therequired water and sand orpremixed lime:sand. Whilemixing add the cement, orcement:lime, gradually andallow to mix in.

Figure 4.8.

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MORTARS 81

• Finally, add the rest of thesand or premixed lime:sandand water necessary toachieve workability.

There is a view that unless thecement is added very carefullyand gradually it will ‘ball’ and notbe evenly dispersed, leading inthe longer term to staining fromthe mortar. To avoid thispossibility others advocate thesecond method:

• Add three-quarters of therequired water and graduallyadd the required cementslowly to ensure a thin pastefree from lumps.

• Add the remaining materialsand water.

Whichever method is used:

• Mix each batch for aconsistent length of time.Three to five minutes, after allthe constituents have beenadded, is sufficient. A shortperiod will produce a non-uniform mix having poorworkability. A long period willproduce a weaker mortarhaving a poorer bond.

• Do not load the mixerto more than its ratedcapacity.

Admixtures• Use admixtures only with

the permission of thedesigner.

• When using plasticisers ormasonry cement (whichcontains plasticisers) do notadd too much water at thestart as these mortarsbecome very fluid as air isentrained.

• Follow the manufacturers’instructions.

• Proposed admixtures shouldbe tested in mortar on a testpanel because some of themaffect the working lifeand/or modify the colour ofmortars. If either effectsoccur the architect orsupervisor should beinformed.

Site batching – using ready-mixed lime:sand

• Care in gauging the cementaccurately is just as essentialas when mixing all theingredients on site.

• Add three-quarters of therequired water and graduallyadd the required cementslowly to ensure a thin pastefree from lumps.

• Add the coarse stuffand water to achieveworkability.

BRICKLAYING• Water may be added for

workability if the mortarbecomes dry but it shouldnever be retempered oncethe initial set has begun.This is particularly importantwhen using ready-to-usemortars.

• When required to iron thefinished joints (bucket handleor weather struck), it is badpractice to iron all the jointsin one operation at the end ofthe day. The mortar placed atthe beginning of the day maybe dry resulting in the ironingtool ‘dragging’ the face of themortar. The recentlycompleted joints, particularlyif low absorbency bricks areused, will be fluid and ironingwill bring the fine particles tothe surface with the risk oflightening the surface andstaining the adjacent brickfaces. Every member of theteam should use a similartechnique otherwise theappearance will vary.

• Newly built brickwork mustbe protected until the mortarhas set. Rain will wash outthe fine particles of cement,lime and pigments. This willchange the colour of themortar, the apparent colourof the brickwork and willpossibly cause permanentstaining. Frost willpermanently damage mortarwhich has not set.

• If frost is likely, protectnewly built brickworkovernight with waterproofinsulation (see Sections 1.2‘Protection of newly builtbrickwork’; 3.1 ‘Avoidingdamage from extremes oftemperature’).

TABLE 4.2. Estimation of quantity of water required

DESIGNATION MEAN WATER DEMAND – LITRES/50kg CEMENT

cement: masonry cement:sand & lime:sand cement:sand plasticiser

(i) 40 – –(ii) 50 35 40(iii) 70 45 50(iv) 100 55 60

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82 ACCESSORIES

• Do not add ‘anti-freeze’admixtures. Although effectivein mass concrete they are noteffective in brickwork becausethe large volume of bricksquickly depresses thetemperature of thecomparatively thin layers ofmortar. Do not build masonrywhen air temperature is at orbelow 3°C and falling.

• Do not lay mortar on frozensurfaces even if the airtemperature rises abovefreezing.

Mortar is not merely ‘muck’used to assemble bricks. It isvital in producing strong,durable and attractivebrickwork. Good workmanshipis vital to the production ofgood mortar.


for use of masonry’ – table 14.(2) BS 8000-3:2001, ‘Workmanship on

building sites’, cl. A.4.2.3.5.(3) Ibid. – cl. A5.1.1.1.

KEY POINTS

■ Use only specified materials.■ Gauge materials accurately.■ Neither undermix nor overmix.

■ Protect materials.■ Protect brickwork until mortar

has set.

4.2 TIES IN CAVITY WALLS

The bricklayer is responsiblefor building-in the typeof ties which have beenspecified in the correctpositions and in a competentworkmanlike manner.Failure, through lack ofskill, care or attention, maylead to damp penetration,distortion, cracking or inextreme cases collapse ofthe wall.

This section deals with tiescommonly used in cavity wallconstruction. The moresophisticated techniques forsupporting and restrainingbrickwork cladding to framedbuildings will be described inanother section.

THE PURPOSE OF WALL TIESTies allow the two slender leavesof a cavity wall to support each

other and produce a strongerwall than one in which the leavesstand independently (fig 4.9).Two leaves acting together willbe virtually as strong as a solidwall only if the bricklayer tiesthem together securely withan adequate number ofsuitable ties.

TYPES OF TIESTies are made in a number ofdifferent shapes and forms fromgalvanised steel, stainless steel,alloys or polypropylene. They areavailable in various lengths to suitdifferent cavity widths (fig 4.10).

The ties will be specified by thearchitect or engineer for particular

Wind

From floorsand roof

Slender singleleaves deflectunder load

Single leaveseffectively tied

Figure 4.9. Effective wall ties strengthen cavity walls.

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TIES IN CAVITY WALLS 83

reasons and the bricklayer shouldnot use any other tie withoutobtaining permission.

POSITION OF TIESThe designer will determine thedistance between ties to give the

required strength and possibly tosuit the placing of thermalinsulation batts or boards. It is notpracticable for designers to specifythe position of each tie and theymust rely on the bricklayer tomake common sense decisions inparticular situations.

There are two useful rules:

• If in doubt ask.• More is better than less.

The bricklayer may berequired to space the ties,horizontally and vertically, inaccordance with therequirements of the BuildingRegulations or therecommendations of theMasonry Code of Practice(1)

which differ slightly. They areboth illustrated here (fig 4.11).

GOOD WORKMANSHIP INPLACING TIES

• Bed all ties at least 50 mminto each leaf – for strength.Position any drip in thecentre of the cavityand pointing downwards(fig 4.12).

• Press ties down into themortar bed – again forstrength – do not place tieson bricks and then lay themortar over them.

• Never push ties into a jointas they will not be effective intying the two leaves together.

• Preferably incline ties(without deforming them)downwards to the outer leaf;never downwards to theinner leaf when they mayprovide a path for water anddampness across the cavityto the inner leaf and into thebuilding (fig 4.13).

• Maintain gauge and consistentthickness of bed joint.

• Do not bend ties to suitcoursing.

• Do not hammer ties,particularly if galvanised.Cracked galvanising will leadto rusting and a weakened

Figure 4.10. Types of ties.

Extra ties at jambs of openings

BuildingRegulations

Maximum 150 mmCode of practice

Maximum 225 mm

Vertical spacingof ties at jambsevery blockcourse or every4th brickcourse (if bothleaves are ofbrickwork)

Maximum450 mm

Maximum 900 mm

NOTE: If one leaf is less than 90 mm thick the maximum horizontal spacing is 450 mm.

Figure 4.11. Maximum tie spacings.

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84 ACCESSORIES

wall. Discard ties withdefective galvanising.

• Clear ties of mortar droppingswhich can conduct moistureacross the cavity and into theinner leaf.

THERMAL INSULATION –CAVITY BATTS AND BOARDS

Insulating cavity batts completelyfill the cavity; they are 455 mm

high and are supported bynormal wall ties placed inthe bed joints 450 mm apartvertically.

Insulating cavity boardspartially fill the cavity andare supported at 450 mmintervals vertically byspecial wall ties incorporatinga device to keep theboard against the inner leaf(fig 4.14).

The problem of coursing thebatts should be solved at groundlevel by carefully examining thedrawings.

The first row of ties forthe purpose of supportinginsulation boards mayneed to be positionedbelow the damp-proof course.If in doubt the bricklayershould ask the brickworksupervisor.

Each batt or part battmust be supported by atleast two ties and eachboard supported and restrainedby at least two ties top andbottom. If the requiredminimum horizontal spacing of900 mm, for structuralpurposes, is too wide forsupporting the insulation theties should be placed closertogether.

Extra ties should be insertedwhere cut boards occurto ensure that they do notlean outwards and bridge thecavity (see Section 4.4 ‘Insulatedcavity walls’ for moreinformation).

Minimum50 mm

Minimum50 mm

Never slopedown toinner leaf.

Level or slopedown toouter leaf.

Figure 4.12. Embedding ties. Figure 4.13. Positioning ties.

Special ties supportand retain boards andmaintain cavity

Closer spacing thanrequired for structuralpurposes

Figure 4.14. Specialties support & retaininsulation boards.

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TIES IN CAVITY WALLS 85

GABLE WALLSSteel straps are used to tie theinner leaf of blockwork of agable wall to the roof trusses orrafters to prevent the gable wallfrom being sucked out by thewind (fig 4.15).

It is therefore important thatthe outer leaf of brickwork issecurely tied to the blockwork(fig 4.16).

The Building ResearchStation recommends thatties are positioned at least300 mm vertically within225 mm of the verge. Inpractical bricklaying terms thismeans that the end tie in everycourse of blocks should bewithin 400 mm of the roofline for roofs with a 35 degreepitch and within 300 mm for a50 degree pitch.

And on a final note . . . Theskill, care and attentionexercised by the bricklayer inbuilding-in ties is the last linkin the chain producing strong,stable, durable, rain resistantwalls.

Reference(1) BS 5628-3:2001, cl. 5.3.5.

KEY POINTS

■ Use only the specified type of tie.■ Position ties strictly as instructed.■ Provide extra ties if needed to

support insulation.■ Provide extra ties around

openings.■ Provide extra ties at the tops of

gable walls.■ Bed ties a minimum of 50 mm

into each leaf.

■ Position any drip in the centre ofthe cavity.

■ Press ties into mortar bed. Donot push them into joints.

■ Incline ties down towards theouter leaf.

■ Do not damage galvanising bybending or hammering ties.

■ If in doubt ask.

Nogging

Block

Steelstrap

Extra wall tiesclose to slopeof gable

300 – 400

225

900Normal horizontal spacing

Figure 4.16. Gable wall tied to roof structure.

Figure 4.15. Ties in a gable wall.

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86 ACCESSORIES

Bricklayers are responsible forbuilding-in damp-proofcourses, including cavity trays,to prevent the penetration ofrainwater and groundmoisture.

If this is not done with skill,care and attention, dampmay cause timber to rot,plaster and decorations todeteriorate and theeffectiveness of thermalinsulation to be reduced.

Repairing damage causedby dampness is invariablyvery expensive and oftendistressing for the occupantsof the building.

DAMP-PROOF COURSES –WHERE THEY ARE USED

DPCs are required in a number ofplaces:

• At the base of external walls,not less than 150 mm aboveground level.

• Similarly at the base ofinternal walls that are built offfoundations rather than theground floor slab.

• Vertically at jambs toopenings in external cavitywalls.

• Horizontally over openings inexternal cavity walls, wherethey are usually called cavitytrays.

• Horizontally at window silland door thresholds.

• Below copings and cappingsto free-standing, retainingand parapet walls andchimney stacks.

DAMP-PROOF COURSES – THEMATERIALS USED

There are two main types of DPCs:

FlexibleThose most commonly used areof bitumen polymer, pitchpolymer or polythene and aresupplied in rolls in a range ofwidths including 110, 220 and300 mm (fig 4.17).

Rolls of bitumen-based flexibleDPCs should be stored on end toavoid distortion. They should bekept in a warm place, particularlyin cold weather, to preventcracking as they are unrolled.

Lead or copper DPCs, usuallycoated with bitumen to preventcorrosion and the possiblestaining of brickwork, are morecostly and are used less often.

RigidTwo courses of DPC bricksbedded in a cement-rich mortar

are often used at the base offree-standing walls where theyprovide a better resistance tooverturning of the wall than doflexible DPCs. They may also beused at the base of external wallsin buildings (fig 4.18a).

• Rigid DPCs of slate or tiles areseldom used today (fig 4.18b).

• Rigid DPCs are suitable toresist rising damp but not thedownward flow of water.

DAMP-PROOF COURSES –BEDDING IN MORTAR

For flexible DPCs, a flat mortarbed should be laid to ensure thatthe DPC will be supportedthroughout its entire length andwidth. The mortar bed shouldnot be furrowed (fig 4.19).

The mortar bed should be freefrom stones, pieces of brick orother hard objects and deep

4.3 DAMP-PROOF COURSES

Figure 4.17. A flexible DPC.

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DAMP-PROOF COURSES 87

enough so that any projectionsor sharp edges will not perforatethe DPC.

The DPC roll should be placedon one end of the wall andcarefully unrolled and pressedonto the mortar bed. This may bedone by sliding a smooth brick orblock along the DPC.

If the roll is not long enough orthere is a change of direction, anew length of DPC should be laidto overlap by at least 100 mm.

It is considered good practice toallow a lap equal to the width ofthe DPC. The overlap should besecured by a jointing compoundor tape.

Care should be taken to usethe correct DPC for the width ofthe wall. The DPC should extendthrough the full thickness of asolid wall and through each leafof a cavity wall and should notbe covered by pointing orrendering.

DAMP-PROOF COURSES INCAVITY WALLS

DPCs should not project into thecavity where mortar droppingsmay build up and lead tomoisture penetration (fig 4.20).

VERTICAL DAMP-PROOFCOURSES AT OPENINGS

When constructing windows anddoor jambs in a cavity wall, thebats that abut the window ordoor frames should be placed sothat the smooth uncut surface istowards the DPC. This will reducethe risk of the cut edge damagingthe DPC (fig 4.21). When closinga cavity at the jambs, a mortarjoint should be formed betweenthe inner leaf and the DPC. To dothis the bats used in the returnwill have to be buttered beforethey are placed in position makingsure that the joint is full.

In many jobs, special cavitycloser blocks may be supplied.

If a window or door frame isto be fixed after the opening isformed the vertical DPCs in the

Figure 4.18a. Two courses of DPC bricksbedded in designation M12 mortar.

Figure 4.18b. Two courses of slatesbonded and bedded in designation M12mortar.

Figure 4.19. Bedding DPC. Figure 4.20. Cavity obstruction.

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88 ACCESSORIES

reveals should project beyond theedge of the brickwork by about5 to 10 mm so as to make contactwith the frame when it is inposition. The DPC should projectinto the cavity by at least 25 mm.

CAVITY TRAYS – WHERE THEYARE USED

Cavity trays are used overwindow and door openings, atsills or any part of theconstruction which bridges thecavity. Their purpose is to preventwater from the outer leafreaching the inner leaf, the cavityinsulation, lintels or window anddoor frames (fig 4.22).

The water collected by the traywill be drained by ‘weep holes’,usually in the form of openvertical cross joints. Sometimes aspecial drainage tube or fibrefilter is built into the joint.

If the trays cannot be formedin one length, any joints shouldoverlap by at least 100 mm andbe sealed to prevent waterpenetrating under the tray.

DPC trays should extendbeyond the end of lintels andwhere specified be fitted witheffective stop ends to preventwater draining into any cavityinsulation which may be installed.

At jambs to openings traysshould lap over vertical DPCswhich in turn should overlap anytrays below, such as those at silllevel.

And on a final note . . . Nomatter how well the architecthas designed the details andchosen the materials, thebricklayer has the finalresponsibility for buildingbrick walls which will keep outthe rain and damp.

Weep hole

Stop end

VerticalDPC

Figure 4.21. Vertical DPC at jamb

Figure 4.22. Cavity trays.

KEY POINTS

■ Bed flexible DPCs on fresh, flatmortar.

■ Any overlaps to be a minimum of100 mm.

■ Do not cover edge of DPCs withmortar or render.

■ Do not allow DPCs to projectinto cavities.

■ Extend DPC trays beyond end oflintels.

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INSULATED CAVITY WALLS 89

The knowledge, understandingand care required to buildan insulated cavity walldemonstrate the modernbricklayer’s need for more thanthe basic bricklaying skills.

WHY CAVITY INSULATION?The most common form ofexternal wall used in recent yearshad a facing brick outer leaf tiedto a ‘light weight’ concrete blockinner leaf with an air space orcavity between. ‘Cavity walls’gradually replaced solid wallsduring the first half of thiscentury as experience showedthat when properly designed andbuilt they were more resistant torain penetration than solid walls(fig 4.23a & b).

Uninsulated cavity walls fallshort of current insulationrequirements which aremost conveniently andeffectively met by buildinginsulating materials into thecavity (fig 4.23c).

Well-designed insulated cavitywalls will meet the highinsulation standards and remainrain resistant only if carefullybuilt, preferably by bricklayerswho understand the specialrequirements.

CAVITY WALLS – GENERALSuccess begins with good basicconstruction techniques. Theseare dealt with more thoroughly inSections 3.3 ‘External cavitywalls’; 4.2 ‘Ties in cavity walls’;4.3 ‘Damp-proof courses’.

Some of the points aresummarised here.

• Wall ties should be level orslope slightly down towardsthe outer leaf with the drippositioned in the centre ofthe cavity and pointingdownwards (fig 4.24a).

• Use only those ties specified,as they may be speciallydesigned for use withinsulating materials (fig 4.24b).

• Particular care must be takento keep the cavities clear ofmortar droppings when cavityinsulation is to be used.

• The cross joints should besolidly filled with mortar tominimise rain penetration(fig 4.24c).

4.4 INSULATED CAVITY WALLS

Figure 4.23a. Traditionalsolid wall.

Figure 4.23b. Traditionalcavity wall.

Figure 4.23c. Insulatedcavity wall.

Level orslope downto outerleaf.

Figure 4.24a.

Figure 4.24b.

Figure 4.24c.

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90 ACCESSORIES

• Provide DPC trays, with stopends, over insulation that isnot built right to the top ofgable end walls (fig 4.24d).

• Provide DPC trays over lintelsetc., and carefully build-in stopends to prevent water runningoff the end of the trays intothe insulation (fig 4.24e).

• Form weep holes to drainwater effectively from thetrays.

TYPES OF INSULATIONThere are three methods ofinsulating cavities (fig 4.25):

(a) Building-in full-fill cavity batts.(b) Building-in partial-fill cavity

boards.(c) Injecting insulation after

construction.

The first two methods requirethe bricklayers to cut, fit and fix

THINGS TO BE DONE BEFOREBUILDING BEGINS

• Check that there is provisionfor storing and protectingthe insulation when delivered.

• Boards for partial fill shouldbe stored flat, never onbearers. Twisted boardswill be difficult to fit closelyto the inner leaf.

Figure 4.24d.

Figure 4.24e.

Figure 4.25a. Full-fill cavity batts. Figure 4.25b. Partial-fill cavity boards. Figure 4.25c. Injection of insulation.

the insulation as they build thecavity wall.

The third method requiresthe bricklayer to build thecavity wall with care, payingparticular attention to anyspecial requirements of theinstallers.

The recommended techniquesfor each method are describedbelow.

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• Check that there is provisionfor protecting partly builtwork and any insulatingmaterials that have beenunwrapped ready for use,from rain and snow.

• When the insulation isdelivered check that it is thecorrect type, height andthickness.

1. BUILDING-IN FULL-FILLCAVITY BATTS

MaterialsBatts are soft and flexible,455 mm high by 1200 mm longand of various thicknesses. Theyare made from layers of mineralfibres treated with a waterrepellant. Water will not penetratethrough the batts but drain downbetween the laminations.

Make provision for protectingbatts before, during and afterconstruction.

Supporting and fixing the battsThe batts completely fill thecavity and are squeezed betweentwo rows of ordinary wall tiesspaced 450 mm apart verticallyand 900 mm apart horizontally(staggered).

Beginning at ground levelThe first row of batts may berequired below ground levelresting on the concrete cavityfill. If necessary cut the batts tofit tightly below the first rowof wall ties. Batts may be cutwith a trowel or a long knife(fig 4.26a).

Alternatively, begin bysupporting each batt on two tiesin the row at DPC level (fig 4.26b).Additional ties will be required atthis level.

Remove excess mortarWater can penetrate where freshmortar from the bed joints in theouter leaf has squeezed into thecavity level with the horizontaljoints between batts (fig 4.27).The water will drain verticallydown the laminations but furtherobstructions may deflect ittowards the inner leaf.

Raising the outer leaf first ispreferredThe risk of rain penetration isminimised by building the outerleaf first.

• This enables the cavity side ofthe joints to be struck flush(fig 4.28).

• Place a protective board tocollect the mortar droppingsand save time and effort later.

• Any mortar left on the top ofthe batts must be removedotherwise water maypenetrate the joint.

• If leading with the outer leaf,build to a height justsufficient to hold the nextrow of ties securely in place.

Batts cut tosuit firstrow of ties

Figure 4.26a. Figure 4.26b.

Figure 4.27.

Figure 4.28.

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92 ACCESSORIES

Raising the inner leaf firstis second bestIf the inner leaf has to be builtfirst:

• After placing the battsbuild one course of bricks(fig 4.29).

• Strike the mortar jointflush on the cavity sideand clean off any mortardroppings.

• Place the batts in the troughwhich has been formed.Never push the batts intodeeper cavities as mortar maybe dislodged and bridge thecavity.

Cutting battsIt will sometimes be necessaryto use small strips cut frombatts. Do not place the endlaminations of cut pieces(i.e. the cut surfaces) in contactwith the external leaf.Otherwise they may conductmoisture to the inner leaf(fig 4.30).

Fitting over extra tiesWhere extra ties are required atwindow and door jambs cut aneat slit for them. Never tear theinsulation or force it over the ties(fig 4.31).

Gable wallsThe insulation in gable wallsshould preferably go up tothe verge. If it does not, the

top of the insulation mustbe protected by a DPC cavitytray that has stop ends toprevent water from the traydraining into the insulation(see fig 4.24d).

2. BUILDING-IN PARTIAL-FILLCAVITY BOARDS

MaterialsInsulation boards are rigid andfixed flat to the cavity face ofthe inner leaf. They may bemade from expandedpolystyrene bead board;extruded expanded polystyreneor polyisocyanurate foam, andglass fibre.

Make provision to storeboards in the dry and on a flatsurface.

Distorted boards will bedifficult to build-in correctly.

Clear air spaceThe clear air space remainingafter the boards have been fixedshould be a minimum of 50 mm.Good cavity wall techniques willkeep the space clear of mortardroppings (fig 4.32).

Supporting and fixing theboardsThe boards are supportedbetween two rows of tiesand held back tightly againstthe inner leaf by special clips.There must be at least twoties top and bottom and sothe ties must be in verticalrows (not staggered) 600 mmapart horizontally. This is lessthan the maximum spacingallowed by the BuildingRegulations for structuralpurposes and is thereforeacceptable.

Path formoisture

Figure 4.29.

Figure 4.30. Figure 4.31.

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Special tiesSpecially designed retainingwall ties must be used and oneexample which has a plasticring clip is illustrated (seefig 4.24b).

Do not fix boards by any othermethod such as wedges or usingthe drips of butterfly ties.

Beginning at ground levelWhether the first row of boardsis required below or aboveDPC, each board must besupported and retained by ties(see fig 4.32).

Building sequence• Build up the inner leaf and

strike the joints flush on thecavity side.

• Remove droppings from thewall tops and prevent theirgetting into the cavity.

• Fit and fix the boards securely,staggering the vertical joints,and butt the horizontaland vertical joint closely(fig 4.33a). Do not overlapthe boards except in the caseof those having speciallyrebated edges.

• Build up the outer leafkeeping the cavity clear ofmortar droppings. Protectinsulation and cavity beforecontinuing the inner leaf(fig 4.33b).

• Do not change fixing positionfrom one leaf to another.

Extra tiesCut neatly around ties – do notimpale or break boards.

3. INJECTION OF INSULATIONAFTER WALL CONSTRUCTION

The insulation is usually injectedsome six months aftercompletion of the building toallow the structure time to dry.The bricklayers will not bedirectly involved as with boardsand batts but carefulworkmanship is still essential ifrain penetration is to beavoided. In particular it isessential to:

• Maintain the cavity width asspecified.

• Keep wall ties clear of mortardroppings.

• Sleeve all vents and seal allopenings.

• Provide a cavity tray at theceiling level in any gable wallif the insulation is not to becarried up to the apex.

Above all seek the advice ofthe insulation contractorbefore building the wall.

Figure 4.32. Clear air space.

Figure 4.33a. Fit and fix board securely.Figure 4.33b. Protect cavity andinsulation.

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94 ACCESSORIES

Effective movement jointsare essential to preventbrickwork in modern buildingscracking from the inevitablemovements which will occurover many years. Architectsand engineers designmovement joints fromexperience and the results ofresearch, but they have to relyon bricklayers to build themovement joints with careand attention.

An understanding of thecauses of movement and theprevention of cracking willhelp bricklayers to apply theirskills more effectively.

THE CAUSES OF MOVEMENTAll materials expand andcontract due to hourly, daily andseasonal changes in temperature(thermal movement) andwetting and drying (moisturemovement).

In addition to thesefluctuating and reversiblemovements, newly fired clay

bricks expand continually overmany years as they graduallytake up moisture. On the otherhand calcium silicate bricks(sandlime and flintlime), likeconcrete products, contract asthey dry after being removedfrom high pressure steamautoclaves.

THE LOCATION OF MOVEMENTJOINTS

Designers try to avoid crackingin long runs of brickwork bydividing them into shorterlengths with vertical movementjoints. These are generally at10–15 m intervals in claybrickwork but may be asclose as 6 m in calcium silicatebrickwork. The joints areusually between 10 and 20 mmwide.

The location and formof movement joints maydepend on the architect’sdecision to either minimiseor emphasise their appearance(fig 4.34).

FORMING MOVEMENT JOINTSIf the movement joints are tofunction effectively and enhancerather than spoil the appearanceof the building they must be builtwith care, attention andunderstanding. It is mostimportant to maintain:

• Joints free from mortar anddebris.

• Full bed joints to the facewithin the movement joint sothat it can be sealedeffectively and neatly.

• Correct and constant jointwidth.

• Verticality.• Bed joints either side of the

movement joint at the samelevel.

Two methodsThere are two basic methods offorming movement joints:1. The specified joint filler ispositioned by suspending orbracing it plumb and in line withthe intended face of the wall. It isthen built-in (fig 4.35a).

KEY POINTS

Building cavity insulated wallscalls for special care and attention.

■ Store correctly and protectinsulation from rain at all times.

■ Protect the top of insulation frommortar droppings.

■ Clear any residual mortar fromtop of insulation. Mortar is apath for water.

■ Cut bed joints flush on cavityside of external leaf.

■ Fit batts and boards closelytogether. Do not use brokenpieces.

■ Fit partial-fill boards close toinner leaf.

■ Support partial-fill boards with atleast two ties to the top andbottom edges of each batt orboard.

■ Use only specified ties andretaining clips.

■ Cut neat slits to fitinsulation over ties – do not tear.

■ Keep air spaces to a minimum of50 mm and clear of mortar anddebris.

■ Follow the manufacturers’instructions – usually enclosedwith each pack.

4.5 VERTICAL MOVEMENT JOINTS

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VERTICAL MOVEMENT JOINTS 95

The joint filler is often asemirigid or closed cellpolyethylene strip. Hemp, fibreboard, cork and other similarmaterials must not be used inclay brickwork as they areinsufficiently compressible toallow the joints to close as thebrickwork expands.

The filler should initially beflush with the external face.Remove sufficient filler to providethe full specified depth and cleanbrick surfaces for the sealant tobe applied and adhere effectively(fig 4.35b).

An alternative method is to cutfrom the filler a piece equivalentto the specified sealant depthand then tack it back beforebuilding-in. The cut piece canthen be easily removed in orderto apply the sealant (fig 4.35c).

It is essential that sufficientspace be left for the specifieddepth of sealant. This will havebeen carefully calculated so thatthe sealant can adjust to themovements in the joint andremain effective for many years.

WARNING! There is now someevidence which suggests thatwhen this method is used themortar may squeeze frombetween the bricks during layingso that the hardened mortarcompresses the filler and reducesthe width and effectiveness ofthe movement joint. If there isany risk of this happening thesecond method described belowwould be preferable.

Inconspicuously located atthe side of a pier

Concealed behind a rainwater pipe

Feature made with singlecant bricks

Contrasting coloured brickseither side of a joint

Figure 4.34. Minimising and emphasising movement joints.

Lath

Brace Jointfiller

Figure 4.35a. Positioning a joint filler.

Strip cut andtacked back

FillerRemovefiller

Figure 4.35b. Creating space for sealant.

Figure 4.35c. An alternative method.

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96 ACCESSORIES

2. The joints are formed bybuilding-in a temporary timberlath for the full depth of the brickskin and the width of the joint.The lath should be braced inposition slightly behind thebrickwork face to prevent itsfouling the bricklayer’s line(fig 4.36a).

The lath should be ‘tapped’from time to time to break themortar bond so that it mayeventually be removed without

damage to the brickwork.The lath should be checkedfrequently for plumb.

When the brickwork reachesthe top of the lath, raise the lathabout half its length in order tomaintain it plumb with theminimum of bracing (fig 4.36b).

All mortar droppings anddebris must be removed from thejoint before it is filled and sealed.

If the length of a wall requiresthat it be divided into

‘manageable’ lengths forbuilding, the use of a temporaryprofile provides a true and plumbsurface for the joint filler andsealant whilst enabling the wallto be run-in for line level andgauge (fig 4.37).

The subsequent section of wallmay be built by ‘pinning into’ the

Timberlath

Brace

Figure 4.36a. Forming an open joint.

Lath raised half its length

Figure 4.36b. Raising the lath.

Cramp

Structural column

Profile

Plumb facesPlan Elevation

Figure 4.37. A temporary profile.

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VERTICAL MOVEMENT JOINTS 97

existing wall for line and gaugewhilst the filler strip or lath canbe placed securely against theend of the wall (fig 4.38).

BUILDING-IN SPECIAL TIESACROSS MOVEMENT JOINTS

Vertical movement joints allowbrick walls to move horizontallyalong their length but it isnecessary to prevent the endsof the leaves on both sides of amovement joint from movingat right angles to their length.This is often done by tyingthem to a steel or reinforcedconcrete frame or to brick orblock walls with special tieswhich have plastic debondingsleeves (fig 4.39a).

The ties are delivered ready foruse with concrete blocks orcalcium silicate bricks (fig 4.39b).

For use in clay brickwork theties must be prepared by pullingthem from the sleeves by anamount equal to the specifiedjoint width to allow for expansionof the brick panels (fig 4.39c).

Filler strip or lath

Line and pin

Sleeved tie

Restraint Restraint

Movement Movement

Sleeved tie Restraint

Movement

Figure 4.38. The next section.

Figure 4.39a. Special ties restrain walls but allow movement.

Figure 4.39b. Ties as delivered for use withconcrete or calcium silicate bricks and blocks.

Figure 4.39c. Ties as prepared for use with claybricks.

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98 ACCESSORIES

APPLICATION OF SEALANTSAfter forming the joints, equalcare must be taken in applying thesealant, preferably by skilled andexperienced specialists. However,as the bricklayer is often requiredto apply the sealant some briefguidance is given here.

When applying sealants, thegolden rule is to follow themanufacturer’s instructionsexactly.

The sealant must adhere to thesides or opposing faces of the jointbut not to the filler or backingmaterial (fig 4.40). Most backingmaterials do not promoteadhesion. Where they do abreaker strip should be used.

Types of sealantSealants may be ready-to-use incartridge form or be supplied intwo parts to be mixed on site.Both types are gun applied. Twosuitable types are:

1. Polysulfide sealants(i) One-part sealants in

cartridges with a curing timeof 2–3 weeks.

(ii) Two-part sealants requiringmixing prior to use andhaving a shorter period forapplication but curing morerapidly within 1–2 days.

2. Silicone sealantsA one part sealant which curesrapidly on exposure to air.

Joint preparationThe filler or backing materialshould be positioned to givethe correct depth for the sealant(fig 4.41).

The joint faces must becleaned free of loose particles,release agents or waterrepellants. The joint faces should

be primed, if required by thesealant manufacturers.

Applying sealantTwo-part sealants must be mixedthoroughly.

The sealant should completelyfill the joint and it should be‘tooled’ as required by themanufacturer to compact thesealant, improve its adhesion tothe joint faces and give aconsistent, smooth, slightlyconcave finish. It is goodpractice to fix masking tapeeither side of the joint tominimise contamination of thebrick face.

AdhesionSealant

Noadhesion

Filler or backing material

Clean jointfaces

Depth

Figure 4.40. Adhesion requirements.

Figure 4.41. Preparation of joint.

KEY POINTS

■ Keep joints clear of mortar anddebris.

■ Maintain the specified width.■ Fill the bed joints flush within

the movement joint.■ Provide the specified depth to

receive the sealant.■ When applying sealants follow

the manufacturer’s instructionsexactly.

■ Pull the sleeves of movementties beyond the end of the tiewhen using them with claybricks.

4.6 REINFORCED AND POST-TENSIONED BRICKWORK

The designers of buildings andcivil engineering structures areconstantly using newtechniques and materials forgreater strength and economy.

Normally, unreinforced brick-work is strong enough to carryloads which bear directly down-

wards on it, e.g. a floor restingon a wall (fig 4.42). Such loadstry to crush the wall which issaid to be in compression.

Lateral loads, like the wind,try to bend the brickworkso that part is in tension.Brickwork is strong in

compression but weak intension, so something mustbe done to resist the tensionor else it will crack and fail(fig 4.43).

This section shows how steelreinforcement can strengthenbrickwork to resist tension.

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As steel reinforced brickworkis becoming more common itis important that bricklayersknow why and understand theneed for good constructionpractice.

1. BED JOINT REINFORCEDBRICKWORK

Steel reinforcement is laid in thebed joint mortar to controlmovement in the brickwork, totie leaves of brickwork togetherand increase brickwork strength(fig 4.44).

2. REINFORCED BRICKWORKBEAMS

Reinforced brick beams can becreated by building ‘U’-shaped

brickwork and then placingsteel and infill concrete in thevoid.

3. GROUTED CAVITYREINFORCED BRICKWORK

Either steel rod or steel meshreinforcement is placed in thecentre of the cavity. The cavityis then filled with either mortaror, more commonly, areasonably liquid concreteor grout (fig 4.45).

Axial load onbrickwork

Brickwork incompression

LOAD

Figure 4.42. Brickwork in compressionfrom axial load.

Brickwork incompressionthis side

Windload

Brickworkin tensionthis side

LOAD TO ONE SIDE OFWALL, i.e. eccentric

Figure 4.43. Brickwork in tension fromlateral and eccentric loads.

Figure 4.44. Bed joint reinforcement.

Cavity fill

ReinforcementFigure 4.45. Grouted cavity reinforcedbrickwork.

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The purpose of filling the cavityis to bind the reinforcement tothe brickwork creating a solidstructure. Cavity fill also protectsthe steel from corrosion. Theamount of protection requireddepends on the type of steel andthe exposure of the particularstructure.

The technique enablesbrickwork to resist lateral loads,such as wind, in buildings andfreestanding walls. It is also usedin earth-retaining walls normallynot exceeding 2 m high.

4. QUETTA BONDREINFORCED BRICKWORK

Steel is contained within pocketsformed by the brickwork bonding(fig 4.46). The pockets arenormally filled with mortar whichbonds the brickwork and steeltogether. Grouted cavityconstruction is more popularthan Quetta bond as the latter ismore difficult to build.

5. POCKET REINFORCEDBRICKWORK

Reinforcement is containedwithin pockets in the rear of thewall between ‘T’-shapedbrickwork (figs 4.47, 4.58). Thereinforcement is joined to thebrickwork by the concrete infillforming a solid structure. Pocketwalls can be faced on one sideonly and, therefore, are normallyused for retaining walls whichhave only one side visible.

6. POST-TENSIONEDBRICKWORK

Special techniques and steelsare used to apply a permanentcompressive load to the

brickwork making it morecapable of resisting horizontalloads. This technique can beapplied to many forms ofbrickwork such as cavity,diaphragm and fin walling(fig 4.48). It is also used in civilengineering structures such asbridge abutments and largeretaining walls.

THE APPLICATION OFREINFORCED AND POST-TENSIONED BRICKWORK

Reinforcing and post-tensioningallows brickwork to carry greaterloads in the same way as does

reinforcing and pre-stressingconcrete. Both reinforcing andpost-tensioning are particularlyuseful when brickwork has toresist lateral loads, e.g fromwind, retained earth, and impactloads (fig 4.49). Because bothreinforced and post-tensionedbrickwork can carry greater loadsthan unreinforced brickwork,which would have to beconsiderably thicker, they areoften cheaper to build.

CONSTRUCTION TECHNIQUESAs both reinforced and post-tensioned brickwork are designedby engineers to BS 5628-2:2000(1),often to carry heavy loads, theymust be very carefully built.

1. HORIZONTALREINFORCEMENT

Horizontal reinforcement isnormally used to:

(a) help control movement inlong runs of brickwork.

Protectedreinforcement

Pockets filledwith mortar

Figure 4.46. Quetta bond reinforcedbrickwork.

Figure 4.47. A pocket-type retainingwall under construction.

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(b) enable brickwork to resisthorizontal loads, e.g. the wind.

(c) provide a reinforced brickbeam either to spread a pointload from say the end of asteel beam over a larger areaof brickwork or to create areinforced brick beam over anopening.

Bed joint reinforcementThe simplest form of horizontalreinforcement is bed jointreinforcement (fig 4.50). Thereinforcement may be placed inevery third or sixth mortar bedjoint depending on engineeringconsiderations.

When using bed jointreinforcement note the following:

(a) Reinforcement wires shouldbe no greater than 6 mm indiameter otherwise it will bedifficult to fit the steel into a10 mm bed joint.

(b) Place reinforcement in a bedof mortar with a minimum of15 mm between the face ofthe brickwork and the edgeof the reinforcement. Thesteel must be surrounded bymortar to develop strengthand protect galvanised steelfrom corrosion.

(c) Some steel manufacturersprovide special jointingsections to avoid having tolap the steel bars where thereinforcement strips meet.Occasionally it may benecessary to cut some of thecross wires to achieve asuccessful 150 mm lapbetween adjoining sections ofsteel. This is not goodpractice and only theminimum amount of steelshould be removed, andwhere possible the crosswires should be maintainedas near as possible to theoriginal spacing.

(d) Normally, suitable stainlesssteel reinforcement is used forexternal solid walls and bothleaves of external cavity walls.Galvanised steel or bitumen-coated steel is normally usedonly for internal walls.

(e) When building-in specialbed joint reinforcement totie two leaves of brickworktogether across a cavity,build up both leavestogether, otherwise it will bedifficult to align the steelbetween the two leaves.

(f) Do not build-in reinforcementacross movement joints. Thesteel will stop the movementjoints working.

(g) The majority of bed jointreinforcement is provided as‘flat’ steel, but if coiledreinforcement is being used

Reinforcement

Post-tensioned wall toa circular brickworkwater tank

Post-tensioned fin towall in sports hall, etc.

Post-tensioned diaphragmwall to a grainstore

Reinforcement

Figure 4.48. Some applications of post-tensioned brickwork.

Figure 4.49. Bridge parapetwall reinforced to withstand vehicleimpact – so hope the ducks!

Figure 4.50. Unrolling bed jointreinforcement.

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(fig 4.50) roll it out carefullyto avoid stressing the wires ordamaging them in someother way.

(h) Make small marks on thefaces of mortar joints to showwhich contain reinforcement.

(i) Extend bed joint reinforcementthe specified length withinthe brickwork, particularly ifit is reinforcing brickworkover openings. Bed jointreinforcement is normally usedonly for light reinforcement.

Other horizontal reinforcementStronger forms of reinforcedbrickwork are used for lintels orbeams over openings. Normally,reinforcement will be containedin a void within the brickworkand will be bonded or joined tothe brickwork by infill concrete orgrout (fig 4.51).

Whichever form of reinforcementis used:(a) Provide a temporary support

for the brickwork until it hascured sufficiently to carry theloads over the opening. This isnormally between 14 and 28days after the infill concretehas been placed. Make surethe temporary support isstrong enough to carry theloads which will rest on itduring construction.

(b) Prevent mortar squeezingfrom the joints duringbricklaying by placing foamor rubber strips on theshutter at the base of joints(fig 4.52).

(c) Because the reinforcedbrickwork will be built in astronger mortar mix, ensurea constant colour of mortarthroughout the brickwork byraking back all the joints inthe reinforced brick sectionand then pointing up withmatching mortar once thetemporary support has beenremoved.

(d) Do not build furtherbrickwork over the openinguntil the reinforced brickworksection has cured sufficientlyto carry the imposed load.

(e) Check the tolerances of thebricks before building theminto the brickwork. As theyrest on the temporarysupport, any variation inthe brick length will show atthe top edge of the bricks(fig 4.51).

2. VERTICAL REINFORCEMENTBrickwork can be verticallyreinforced to increase its bendingstrength.

For example, a gate hung on atall brick pier will try to pull it

over (fig 4.53). To resist bendingand cracking in the brick pier,vertical reinforcement can bebuilt into the centre.

The mass of earth behind anunreinforced retaining wallmay cause the brickwork tofail in tension. Steel placed inthe wall can help resist theload by preventing the wallsliding forward or bendingand cracking.

Vertical reinforcement can beincorporated in brickwork inseveral ways. Each has its ownconstruction method:

Grouted cavity reinforcedbrickwork (see figs 4.45 & 4.54)(a) Construct reinforced

concrete foundation withreinforcing starter barstypically 600 mm high,projecting from the topface. Lap reinforcement inthe grouted cavitybrickwork over the starterbars to join the wall to thefoundation (fig 4.55).

Gate pullsunreinforced pier over

Figure 4.51. Forming pocket forhorizontal reinforcement.

Figure 4.52. Foam strips placed onshutter to prevent mortar squeezing out. Figure 4.53. A gate pier.

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(b) Build one leaf of brickworkoff the foundationincorporating wall ties asspecified. Do not build theleaf higher than 16 coursesotherwise it may fall over.

(c) Clean all mortar snots off therear face of the brickworkand off the ties and thefoundation area. Take care toavoid injury on the projectingwall ties.

(d) Lap the reinforcementagainst the starter bars

by the length specified(fig 4.55). Support thereinforcement within thecavity, typically by tying thereinforcement to the wallties.

If ordinary mild steelreinforcement is used withstainless steel wall ties do notallow the two steels to touch,otherwise bi-metallic corrosioncan occur. A non-metallicmaterial should be used to fixsteel reinforcement to wall ties.

Place steel centrally in thecavity except where it is lappedto adjoining steel. Plastic spacershelp to do this.

Steel is usually placed in thecentre of cavities to ensure thatthere is adequate infill concretecover to the steel to preventcorrosion of unprotectedreinforcing steels and to providebond between the infill concreteand the steel.

(e) Construct the other leaf ofbrickwork 6 courses high,removing all mortardroppings from the cavity.Use cavity battens to preventmortar entering the cavity orplace a piece of polythene inthe base of the cavity tocatch the mortar droppingsand then when thebrickwork is completed pullthe polythene out of thecavity complete with thedroppings (fig 4.55).

(f) When the mortar has startedto set and the brickwork isstrong enough to resist thepressure of the infill concrete,typically after 12–15 hours, fillthe cavity with concreteas specified. Make sure novoids are left in the infillconcrete using a small pokervibrator to force the air out (fig4.56).

Finish the concrete face50 mm below the bed face

Figure 4.54. Grouted cavity wall underconstruction – note loop ties.

Mesh reinforcementtied to starter bars

Outer leaf

Loop ties

Inner leaf

Starter bars

Polythene sheet tocollect mortardroppings

Foundation

Figure 4.55. Grouted cavity brickwork construction –showing a method of collecting mortar droppings in cavity.

Timber cavitybattens both sidesof reinforcementto collect mortardroppings

Infill concretestopped 50 mmbelow bed face ofbricks

Figure 4.56. Grouted cavity brickwork construction – showingan alternative method of collecting mortar droppings in cavity.

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104 ACCESSORIES

of the lower leaf ofbrickwork to avoid a straightline of weakness throughthe brickwork (fig 4.57).Take care that the infillconcrete is not over-vibratedand separates out.

(g) Repeat this operation ensuringmortar droppings arecleared from the groutedcavity section before theinfill concrete is placed. Wherethere are several sections ofgrouted cavity wall being builtit may be necessary to providetemporary ends to the cavityto prevent the infill concreteescaping.

It is important that any facebrickwork is protected whileinfill concrete is placed, toavoid staining the face of thebrickwork.

Quetta bond reinforced brickwork(see figure 4.46)(a) Lay the bricks carefully to

ensure a constant size ofpocket around the verticalreinforcement. Incorporatestarter bars at the base of thewall to join the verticalreinforcement within the wallto the foundation.

(b) The spaces between thesteel and the brickwork areoften filled with DesignationM12 mortar as bricklayingprogresses. It must be wellcompacted around the steelwhich will have to beprotected either asgalvanised steel or asstainless steel. With mildsteel, concrete is normallyused to fill between the steeland the brickwork.

Because the void in whichthe infill concrete has to beplaced is narrow, take care to

ensure that the concrete doesnot hang on the side of thevoid but is well compacted inplace.

Pocket reinforced brickwork (fig 4.58)(a) For ease of construction the

brickwork is normallycompleted before thereinforcing steel is placed.

(b) Keep all mortar out of thepocket and take particularcare with the bonding aroundthe pocket to ensure thesides of the pocket are builtinto the main brickwork asspecified.

(c) When the brickwork iscomplete, place thereinforcement steel in the

50 mm

50 mm

Freshgrout lift

Previousgrout lift

Maximum groutlift 450 mm

Figure 4.57. Grouted cavityconstruction – placing grout in low lifts.

1. Starter bars

2. Concrete foundation

3. Pockets formed in brickwork for reinforcement

4. Reinforcement placed in pockets

5. Concrete infill

6. Retained earth

Figure 4.58. Pocket reinforced brickwork – showing normal sequence of buildingoperations. (The damp-proof membrane to the retaining face has been omitted for clarity.)

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pocket lapping over thestarter bars at the base. Fixshuttering at the rear of thepocket prior to the infillconcrete being poured intothe void.

Vibrate the concrete intoplace, taking care not todisturb the brickwork. Thisensures that the infillconcrete forms a solid massaround the steel within thebrickwork pocket.

POST-TENSIONED BRICKWORK(fig 4.48)(a) Larger diameter reinforcing

bars are normally used forpost-tensioned brickwork.These may require atemporary support to stopthem bending and damagingthe green brickwork duringconstruction.

(b) The bars are often containedin voids, cavities or ductswithin the brickwork. Eventhough the post-tensionedsteel is often left ungroutedwithin the void, cavity or ductit is still important that allmortar droppings are clearedfrom the void around the steel.

(c) If specified, construct slopingconcrete plinths at the baseof the void around the post-tensioning bars and formweep holes through thebrickwork to allow the waterto drain.

(d) At the top of the post-tensioned brickwork wall areinforced concrete cappingbeam will normally beconstructed to spread theload produced by thetensioning of thereinforcement (fig 4.59). Thisenables the force produced

by the tensioning to bespread evenly over thebrickwork.

The reinforced concretebeam may be cast in situ.Otherwise it will bepreformed, in which case bedit on the brickwork on fullmortar joints.

(e) Tension the reinforcementafter the specified period,not less than 14 days.Retension 14 days later toallow for any settlementwhich may have occurred inthe brickwork due to theload imposed on it.

GENERAL POINTSWhichever form of reinforced orpost-tensioned brickwork is used,certain bricklaying operations areimportant:

(a) Locate the steel carefullyin the brickwork inaccordance with theengineer’s drawings andspecification.

(b) Take care to support thesteel during bricklaying sothat steel does not causeinjury to the bricklayers ordamage the greenbrickwork. In particular,cover the ends of rods toprevent eye injuries.

(c) Fill all joints in the brickworkcompletely. The brickwork willnormally carry very high loads.

(d) Mix the mortar accuratelyand use quickly as the highercement content will lead to afaster set. Reinforcedbrickwork normally requireshigher strength mortars suchas Designation M12 (1:1/4:3)and Designation M6(1:1/2:41/2).

(e) Accurately formreinforcement lap jointsas specified.

(f) Remove all excess mortarfrom the reinforcement andties from the voids. Mortarsare weaker than the infillconcrete and should not bemixed with it.

(g) When placing infillconcrete, cover the facebrickwork to protect itfrom concrete splashing. Becareful not to overfill withgrout as spillage is difficultto remove from the facebrickwork.

(h) Damp-proof membranes willoften be brushed, sprayed orstuck on the rear face ofreinforced brickworkretaining walls. In whichcase fill all joints on the rearface and finish with a firmsurface. Unless otherwiseinstructed form a shallowbucket handle profile for therear face.

(i) Reinforced and post-tensioned brickwork must becured properly and protected

Figure 4.59. The principle of post-tensioned brickwork.

Tensioning nut

Padstone

Brickwork

Reinforcement

Anchorage

Post-tensioningcompressesbrickwork

Lateralload

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106 ACCESSORIES

from saturation duringconstruction (see Section 1.2‘Protection of newly builtbrickwork’).

A SPECIAL NEED FORTEMPORARY PROTECTION

When construction of a sectionof reinforced brickwork has beencompleted, ensure thattemporary protection isimmediately provided to preventrainwater percolating throughconcrete or mortar infill andthen to the facing brickwork, asthis can lead to serious limestaining. Design of thecompleted structure should havefeatures that give permanentprotection against such wetting,e.g. properly designed and

installed copings or roofoverhangs, and damp-proofmembranes on the rear surfaceof retaining walls.

Reference(1) BS 5628-2:2000 ‘Structural use

of reinforced and prestressedmasonry’.

KEY POINTS

■ Position steel correctly in thebrickwork.

■ Keep mortar droppings clear ofbrickwork ties and the base ofvoids around the reinforcement.

■ Properly form steel laps.■ Support steel to avoid injury to

bricklayers and damage to greenbrickwork.

■ Use only specified mortar andmix properly.

■ Completely fill all mortar jointsand finish as specified.

■ Protect facework during placingof infill concrete.

■ Protect all brickwork afterconstruction and duringinclement weather.

■ Reinforced and post-tensionedbrickwork is an engineeringstructure and the higheststandards of brickwork arerequired.

■ Do not subject brickwork toloading other than self-weightuntil it has cured sufficiently.

4.7 BRICKWORK ON METAL SUPPORT SYSTEMS

This section deals withbuildings above two storeys inheight that have thebrickwork outer leaves ofcavity walls supported by asystem of metal angles and/orbrackets fixed to structuralframes.

Bricklayers may themselvesfix a system or build on onefixed by others. Either way,systems should be fixedstrictly to the designer’sspecification and manufacturer’sinstructions.

If you are ever in doubt, aska supervisor. Mistakes areusually expensive to put rightand may be dangerous.

VERTICAL SPACING OFSUPPORT SYSTEMS

Systems are normally locatedat every storey or second storey(fig 4.60). They are designedspecifically to support thebrickwork for each particularbuilding.

Concrete frames shrink as theycure and creep under load. Steelframes are considereddimensionally stable. Becauseclay brickwork slowly expands fora long time, horizontalmovement joints are normallypositioned between the top ofthe brickwork and the undersideof each metal support system,whether the structural frame is of

Supportlevel and movementjoint

Expandingbrickworkouter leaf

Supportlevel andmovementjoint

Shrinkingstructuralframe

Figure 4.60. Brickwork outer leafsupported at every second floor.

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BRICKWORK ON METAL SUPPORT SYSTEMS 107

concrete or steel. The joints,which are usually designed toaccommodate an expansion ofbrickwork of up to 1 mm permetre, will therefore becompressed over a period oftime (fig 4.61).

TYPES OF METAL USED FORSUPPORT SYSTEMS

For buildings of more thanthree storeys, the supportsystem will always bemanufactured from austeniticstainless steel. Althoughgalvanised mild steel ispermitted in buildings of threestoreys and less, in practice, thebuilding specification or localregulations will invariably call foraustenitic stainless steel which iscorrosion resistant with a verylong maintenance-free life.Galvanising is a sacrificialcoating, has a limited life, andthe unprotected mild steel willcorrode and may damage thebrickwork.

The specification for austeniticstainless steel is normally aminimum 18/8 composition

(18% chromium, 8% nickel);Grade 304 is the most popular ofthe 18/8 stainless steels. That forgalvanised steel, if used, isnormally Grade 43 mild steelwith a minimum post galvanisedcoating of 940 g/m2.

FIXING DISSIMILAR METALSTOGETHER

When dissimilar metals are incontact and moisture is present,electrolytic action increases thecorrosion rate of the less noblematerial, e.g. when stainless andmild steel are in contact, thecorrosion rate of the mild steelincreases.

In many cases the protectivecoating provided to the mildsteel may be sufficient toprevent this action. Wherethis is not the case the designermay decide to preventelectrolytic action by one oftwo methods.

1. Isolation of two metals.Impervious packing, sleeves andwashers separate stainless steelfrom mild steel (fig 4.62).

2. Exclusion of moisture.Jointing compound and a paintsystem overlapping the joint by aminimum of 20 mm may also bespecified. Thick water-resistingplastics or mastic coatings shouldbe used.

TYPES OF SUPPORT SYSTEMSBrickwork support systems areusually selected from one ofthree types:

1. Continuous angle systems.Lengths of continuous angle ofup to 3 m long, with horizontalslotted holes along the verticalleg, are fixed to concrete witheither site-drilled expansion boltsor serrated ‘T’-head bolts intovertical cast-in toothed channels(fig 4.63).

10 mm open joints are leftbetween adjoining lengths ofangles to allow for thermalexpansion of the angle as well asbuilding tolerances.

Angles may be bolted directlyto steelwork with stainless steelnuts and bolts (See paragraphabove ‘FIXING DISSIMILAR METALS

TOGETHER’). Examples are given inthe BDA/BSC joint publication‘Brick cladding to steel framedbuildings’.(1)

Compressiblefiller

DPCBracketAngle

Sealant

Figure 4.61. Typical detail of a supportsystem.

Structuralmild steel Isolation

sleeve washerand packing

Stainless steelbolt, washerand nut Stainless steel angle

Vertical cast-intoothed channels

Thermal insulation

Pistol bricks

Figure 4.62. A typical method of isolatingtwo dissimilar metals.

Figure 4.63. Continuous angle systems.(Cavity tray omitted for clarity.)

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108 ACCESSORIES

Depending on the mass ofbrickwork to be supportedand the cavity width specified, theangle may be typically 8–10 mmthick. Pistol bricks may be used toavoid an excessively thick joint inface of the wall (fig 4.64).

2. Bracket angle systems.Much smaller angles are weldedto brackets to suit a particularcavity width. The brackets arenormally fixed with ‘T’-headbolts into a continuoushorizontal channel cast intoconcrete (fig 4.65).

The angle thickness willnormally be 5 mm or 6 mm. Itmay sometimes be built into ajoint without using a pistol brick

but the joint will be wider than10 mm.

3. Individual bracket systems.Bricks are supported on individualbrackets which have stiffenerswhich fit into the vertical crossjoints. The brackets are fixed in asimilar manner to bracket angles(fig 4.66).

The support bases are usually4 mm thick and are built into anominal 10 mm joint.

Summary of applicationsThe three types of systemsdescribed previously are typicallyused as follows.

Continuous angle• Usually for cavities less than

75 mm.• To close the cavity where the

underside of the support willbe seen.

Bracket angle• For cavities from

50 mm–150 mm.• For fixing directly to uncased

structural steelwork.

Individual brackets• For brickwork that is curved

on plan.• For features such as arches

and suspended soldiercourses.

BUILDING WITH CONTINUOUSANGLE OR BRACKET ANGLE

SYSTEMS

Accurate positioningAngles should be correctlypositioned, levelled and securelyfixed to the frame. There shouldbe room underneath angles toallow for vertical expansion ofthe brickwork below andshrinkage of any concrete frame.

Where 10 mm joints are leftbetween lengths of adjoiningcontinuous angle, in order toallow for tolerances and thermalexpansion, it may be necessary toseal them with a local DPC toprevent water crossing the cavity.Joints in bracket angle systemsmay be left open.

FixingAll fixings should be tightenedto the specified torque and theoverall thickness of any shimsshould not exceed the suppliersrecommendations, usually12 mm or 20 mm (fig 4.67).Shims should be of the‘horseshoe’ type, giving supportto the full depth of the back ofthe angle including the heel

Insulation

Continuousangle8–10 mmthickWeep holes atmaximum of1 m intervalshorizontally

Pistol brick toreduce jointthickness

Figure 4.64. Continuous angle systems.

Continuouscast-inchannel

Brackets fixedwith ‘T’-Headbolts to channel

Continuous angle5–6 mm thick

Figure 4.65. Bracket angle system.(Cavity tray omitted for clarity.)

Brick supportbases 4 mmthick

Bracket stiffenersfit into verticalcross joints

Figure 4.66. Individual bracketsystem. (Cavity tray omitted for clarity.)

Maximum shimmingto suppliers’recommendations

Minimum rdsbearing forbrickwork

Minimum20 mm

Allowance forexpansion ofbrickworkbelow

23

Figure 4.67. Positioning and shimmingangle.

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(fig 4.68). Round washers mustnot be used as they will allowthe angle or bracket to deflect.

Building the brickworkDesigners’ views differ on thedetailed solution to this relativelyrecent technique of supportingouter leaves of brickwork on steelangles. Consequently, bricklayersmay be required to position theDPC either on the angle or onecourse above. A typical method ofbuilding each is described below.

1. DPC above the first course.(fig 4.69)Bed the first course on the angle.Use a reduced mortar bed ifinstructed to keep the overalljoint thickness to a minimum.Rebated bricks (sometimes calledpistol bricks) may be specified.

In order to improve the bondbetween the first course and theangle some specifiers may requirea polymer bonding admixture tothe mortar, such as styrene-butadiene rubber (SBR) in whichcase it must be used strictly inaccordance with themanufacturer’s instructions.Others may have specified aprofiled surface to the top of theangle or mesh to be tack weldedto it.

Continue building the outerleaf including the DPC and ties tothe inner leaf. Because thismethod isolates one coursebetween the angle and the DPC,some designers specify ties, fixedback to the support system butadjustable horizontally, forbuilding into cross joints in thefirst course (fig 4.69).

2. DPC on support angle.Normally, DPCs will be beddedon the angle before bedding thefirst course although somedesigners may require the DPC tobe laid directly on the angle toprovide a slip plane between itand the brickwork which havedifferent movementcharacteristics. It is likely to besimpler to hold a flexible DPC inplace while bedding the bricks,rather than a thicker, stiffermaterial.

The bricks for the first coursemay be rebated in order tominimise the visible joint thickness.

Whatever the position of theDPC ensure that open cross jointsor weep holes are formed at amaximum of 1 m intervalsimmediately above the DPC(see Section 4.3 ‘Damp-proofcourses’).

Half-brick leaves should have aminimum bearing on the anglesof 2/3 the width of the leaf,approximately 70 mm. The toesof angles should be at least20 mm back from the face ofthe brickwork (fig 4.67).

BUILDING WITH INDIVIDUALBRACKET SYSTEMS

Positioning and fixing bracketsUnlike continuous angleand bracket angle supportsystems, individual bracketscannot be preset ready to laybricks. The following procedureis typical.

• Set out brackets at brickcentres and bolt loosely tothe cast-in channel (fig 4.70).

• Place bricks on brackets andadjust the latter so that thestiffeners are in the centre of

Figure 4.68. Use of correct shims.

Cavity tie

Weep holes at maximumof 1 m horizontal spacing

DPC

Tie

Compressible filler withsealant

Figure 4.69.

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110 ACCESSORIES

cross joints and align eachbracket and tighten the‘T’-head bolt to the correcttorque (fig 4.71).

Building the brickwork• A thin bed of mortar is

normally applied to eachbracket in order to alignand level the bricks.

• Build the remainingbrickwork including anyDPCs and wall ties.

It may be advantageous tobuild the first course off thebrackets using bricks selected forconsistent length and height.

BUILDING A SOLDIER COURSEOVER AN OPENING

Bracket systems are often used tosuspend brickwork over windowsand openings when the architectdoes not want a lintel or supportangle to be visible.

The individual brackets arepositioned and tightened asdescribed previously (fig 4.72).

A temporary support is fixedfirmly to carry the weight of thesoldier course, withoutmovement, until the mortar sets.

The soldier bricks are perforatedwith at least two holesapproximately 25 mm in diameter.

The soldier course is built fromone end, three bricks at a time,completely filling both the holesand the joints with mortar. Shortlengths of stainless steel stitchingrods are pushed through themortar holes to span betweentwo brackets (fig 4.73).

The soldier course is continuedin sets of three bricks untilcomplete (fig 4.74).

A similar method can be usedto build arches that cannot bedesigned to be self-supporting.The brackets are fixed to cast-inchannels in the face of theconcrete, radiating aroundthe arch.

It is necessary to preventmortar squeezing from thevertical joints and under theshutter/temporary support andstaining the face of the bricks.Foam rubber strips may beplaced in the bottom of eachvertical joint and when thevertical joint is formed the faceof the vertical joint should beraked back.

When the brickwork is cured,say 14 days after constructiondepending on the load imposedon the brickwork and theweather conditions, thetemporary supports are removed,the foam strips removed andthen the vertical face and thehorizontal soffit face of the jointpointed up in matching mortar.Bricks selected for consistency ofsize will normally be required forthis form of construction and thehanging system and theperforation pattern of the bricksmust be compatible.

Figure 4.70. Individual brackets inposition.

Figure 4.71. Individual bracketslevelled and tightened.

TemporarySupport

Figure 4.72. Suspension stirrups builtinto vertical cross joints.

Figure 4.73. Stitching rods pushed intomortar filled perforations.

Figure 4.74. Brick leaf built off individualbrackets.

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BUILDING-IN WALL TIESThe need for correct, properlybuilt-in cavity wall ties at thespecified spacing was pointed outin section 4.2 ‘Ties in cavity walls’.

The need is even more criticalwhen brick panels aresupported on metal anglesystems. Any deflection of thestructural frame or supportsystem may be transmitted tothe brickwork leaf which shouldbe restrained by being tied tothe inner leaf and/or thestructural frame.

In addition, the top of cavitywall panels may be tied to theframe just below the horizontalmovement joint, for lateralsupport.

A typical tie, giving lateralrestraint but allowing verticaldifferential movement, is shownin fig 4.75.

BUILDING ‘CORBELLED’BRICKWORK

True corbelling, as described insection 5.8, cannot be used inmost modern cavity wallsituations. Normally, if acorbelled appearance is requireda support system is used, oftenwith inverted plinth bricks(fig 4.76).

The first course is built on asupport system as previouslydescribed. The remaining corbelcourses are tied back to thestructure at every bed joint.

Depending on the extent of thecorbelling, the number of coursesbuilt at one time should belimited to possibly only two.

The brickwork above the corbelledcourses is carried on one of thesupport systems that have beendescribed. Plinth bricks invariablyrequire considerable modificationto suit a system. Temporarysupport of the plinths duringconstruction and measuresto prevent mortar staining of thebricks and consistency of mortarcolour must be taken.

Reference(1) R. E. Bradshaw, G. Buckton,

S. W. Southwick. ‘Brick cladding tosteel framed buildings’. The BrickDevelopment Association andBritish Steel Corporation.September 1986.

Fixed tostructuralframe

Sliding tiesbuilt intobrick andblockwork

Figure 4.75. Typical sliding restraint ties.

Figure 4.76.

KEY POINTS

■ Check that the structural frame iswithin specified tolerancesbefore fixing a support system.

■ Ensure that any shimming doesnot exceed the maximumspecified.

■ Ensure that approved full-depthshims are used, not just roundwashers.

■ Check that the support is atthe correct level and that

there is sufficient roomunderneath to allow for anexpansion joint.

■ Check that all bolts are tightenedto the correct torque setting.

■ Ensure a minimum of 70 mm–75 mm bearing for the brickwork.

■ Build-in the correct cavity andrestraint ties as specified.

■ Follow manufacturers’instructions – if in doubt ask.

Strips offoamed rubberin base of crossjoints

Temporarysupport

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Some brickwork features requirespecific knowledge and skill tofacilitate their construction.

This section gives detailedguidance on a variety ofconstruction features which,

between them, illustrate theprinciples of several specialprocedures.

5 SPECIFIC CONSTRUCTIONS

5.1 COPINGS AND CAPPINGS

Copings and cappings aredesigned to protect the tops ofwalls and finish them neatly.In practice they will do so onlyif skill and care is constantlyexercised by the bricklayer.

THEIR PURPOSEOn brick parapet, freestandingand retaining walls they greatlyreduce the quantity of waterpenetrating and possiblysaturating the brickwork below.

Both bricks and mortar thatare frequently saturated shouldbe specified as frost resistant inorder to avoid frost attack.Saturated mortar may alsocrumble from sulfate attack ifit is not correctly specified,gauged and mixed.

The appearance of brickworkthat becomes saturated may bespoilt temporarily by efflorescenceor virtually permanently bylime-leaching or algae. In the longterm badly made joints betweencoping units may cause localsaturation and staining.

DEFINITIONS• Copings

Copings have an overhangwith a throat to shedrun-off rainwater clear of

the brickwork immediatelybelow (fig 5.1).

• CappingsCappings are usually flushwith the wall below. Theymay have an overhang butno throat (fig 5.2).

MATERIALSCopings, cappings and mortarjointing will usually suffersevere saturation and freezingand should have beenspecified for their durabilityunder such conditions. Copingsand cappings may be madefrom:

• Precast concrete• Natural or artificial stone• Bricks – either standard or

special shaped bricks• Brick and tile creasing• Terracotta• Slate• Metal or plastic – not usually

fixed by bricklayers.

Figure 5.2. Cappings.

Figure 5.1. A coping.

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COPINGS AND CAPPINGS 113

PRECAST CONCRETE ANDSTONE COPINGS

• Damp-proof coursesCopings should be beddedon a damp-proof course toprevent moisture reachingthe brickwork through theinevitable fine cracks whichwill develop between themortar and the coping units.The DPC should preferablyproject about 10 mm fromthe face of the wall. The DPCand coping should bebedded in one operation onto fresh mortar to achieve themaximum bond with thewall below.

• Method of alignmentIf the coping is above eyelevel, as on a parapet or highboundary wall, the lower edgeshould be ‘lined-in’ (fig 5.3).On a low wall the upper edgeshould be aligned (fig 5.4).

For a narrow coping only a frontline is necessary (fig 5.5).

Align lower edges

Align upper edges

One line sufficientfor narrow copings.Two lines essentialfor wider copings

Figure 5.5. Narrow and wide copings.

Figure 5.4. Below eye line.

Figure 5.3. Above eye line.

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• Fitting, cutting andbeddingDetermine how many copingunits and cuts will be required.Allow for 6–10 mm widejoints between units. Cut unitsshould not be positionedat the ‘free’ end of a wall(fig 5.6a). If the coping isbetween piers, place equal cutlengths at each end (fig 5.6b).

For neat straight cuts and tominimise breakages use a disccutter. Bed a coping unit at eachend and pull a line between.Before bedding the rest of theunits set them out ‘dry’ toestablish a suitable andconsistent gauge.

• Bedding and jointingmortarGauge mortar strictly asinstructed because theproportions will have beenspecified to produce adurable mortar. The mixwill usually be 1:1/4:3,cement:lime:sand(a designation M12 mortar).

The cement, sand and anypigments should each beobtained from a single sourcethroughout the job so thatthe mortar will not vary in

colour and make the finishedwork look patchy.

• Movement jointsCare should be taken toposition movement joints incopings and cappings strictlyas specified. They shouldcoincide with movementjoints in the wall below.Movement joints must bekept free of mortar droppingsand debris and filled only withthe specified jointing material– never with mortar as it isnot compressible.

• ThroatsThe throat should becontinued through thejointing material otherwisestaining or deterioration of

the brickwork below mayoccur (fig 5.7).

• CrampsBrush out any dust fromthe slots and dampenthem before bedding thenon-ferrous cramps usingmortar of the same mix asthe bedding mortar.Such cramps are oftenused on sloping parapet gablewalls (fig 5.8). They mustnever be fixed across amovement joint.

Brick copings and cappingsBrick copings may be built fromstandard half-round orsaddleback units or fromproprietary units.

Line pushed in at both ends and‘blocked’ out with bricks

Coping units set out dry before bedding in mortarWhole unit at‘free’ end of wall

Cut unitagainst pier

Line pin

Mortar joints solidly buttered as units are bedded

Equal cuts at each end

Maintain throatunder coping byrubbing withjointer across themortar jointsbetween unitsFigure 5.7. Maintain throats.

Figure 5.6b. Wall between piers.

Figure 5.6a. Wall with ‘free’ end.

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When bedding 65 mmthick units, ensure that thevertical joints are fully butteredand filled as the work proceeds(fig 5.9).

Preferably begin by building‘starter blocks’ on the ground orother suitable surface and allow toharden. Then bed one at each endof the wall and pull lines through.

Position two lines, one back andone front, to prevent the unitsfrom ‘tipping’ especially whenusing half-round coping bricks.

If the dimension of the brickcoping units, along the length ofthe wall, is greater than thestandard 65 mm (some are215 mm) they should be builtas described above for precastconcrete and stone copings.

Cappings, if flush with thewall below, are simpler to‘line-in’.

All the comments concerningDPCs, Bedding and jointingmortars, Movement joints andThroats made under the heading‘Precast concrete and stonecopings’ apply when buildingbrick copings.

• Damp-proof courseAfter building a brick-on-edgecapping it is advisable to lay acourse of bricks dry on topwhile the mortar sets in orderto improve its bond with thebricks and the DPC (fig 5.10).

Some consider that the top ofthe wall will be more stable ifthe DPC is placed under thecourse below the capping.

This consideration does notapply where the DPC is part of aproprietary interlocking cappingsystem.

The DPC should be left slightlyprojecting or cut flush asspecified. It should never be cutback from the face and pointedover, as this often leads to spallingof the mortar or even the bricks.

• AlignmentLines (•) should be positionedto prevent ‘tipping’ and‘waving’. Where possibleuse one line to maintain

Coping to gablewall

Non-ferrous cramp set ingroove formed in coping

‘Butter’ and fillvertical joints as thework proceeds

Figure 5.9. Clay saddleback coping.

Figure 5.8. Fixing cramps.

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alignment of a ‘preferred’ faceor ‘give and take’ if the brickdimensions are not consistent.Use a line on the other side toprevent ‘tipping’ (fig 5.11).

• Long wallsThe lining-in of long stretchesof copings and cappingsnecessitates the ‘eyeing-in’or ‘sighting’ of intermediatepoints, between which theunits are run-in, to check thatthe line is tight enough. Tingle

plates prevent long lines fromsagging and must also be‘sighted’ or ‘eyed-in’ (fig 5.12).

• Brick and tile creasing courseThis consists of abrick-on-edge course seton two courses of tiles knownas creasing courses.The tiles may be virtuallyflat with no nibs. Tiles withcontinuous nibs which arecarefully built to form acontinuous throat may enable

brick and tile creasing coursesto function as a coping if aflexible DPC is also included inthe assembly. The DPC shouldbe sandwiched in mortarbelow the tile creasing courses.The creasing courses alone willnot prevent the downwardpercolation of water into thebrickwork below.

Lay two courses of creasing tilesin mortar to ‘half bond’ takingcare to ‘wipe on’ mortar at eachbutt joint between tiles. The firstcourse should be lined-in alongthe lower edge and the secondcourse along the upper edge.Creasing tiles are seldom regularin shape and some ‘give and take’may be necessary (fig 15.13).

Select the required number ofbricks for the capping course andcheck for consistency of size,discarding any with excessivevariation from the average lengthand width. The guidance given forthe selection of bricks for a soldierarch is appropriate (Section 5.5).

A course of ‘dry’ bricks placedwhile the mortar sets may helpadhesion of top course

Dpc bedded on a fresh mortarfollowed quickly by the nextcourse

Dpc left projecting or cut flush,never cut back from surface

Alternative lower position forDPC often preferred

Figure 5.11. Special shapes – brick-on-edge cappings.

Figure 5.10. A standard brick-on-edge capping.

Second line toavoid ‘tipping’

2 linesrequired

Half-roundcapping

Doublecant

Doublebullnose

Line toalignpreferredface

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‘Pins’ pushed into the mortarjoint around which the lineis wound.

Tinglesighted fromend to end

Brick-on-edge beddedat mid-point and tingleused to prevent linesagging


Second line totop of course

First line to bottom ofcourse

Figure 5.13. Laying a creasing course.

done by tightening rather thanopening joints.

The brick to be laid should bebuttered and pushed against theexisting brickwork (fig 5.15a).

Figure 5.12. Long walls.

End block of 3 bricksbedded to gauge onfloor unless a specialone-piece stop end isspecified

Face sideline to givelevel andstraightness,back line togive levelonly

Steel pinsecured incross joint

Figure 5.14. Laying the brick-on-edge capping.

The brick-on-edge courseshould be bedded, the verticaljoints fully buttered as the workproceeds and any frogs solidlyfilled.

It is best to begin by preparingend blocks of three bricks unlessspecial stop ends are specified.

When the blocks have set, bedone at each end to which a linemay be fixed (fig 5.14).

Set out the gauge to avoidcutting bricks. This is preferably

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Remove surplus mortar alongthe line of the joint to avoidsmudging the faces of the bricks(fig 5.15b).

Lay bricks to a line on the frontand back top edges. This keepsthe whole course in line andprevents ‘waving’. Check thegauge frequently to avoid asudden change in joint width.

To place the last brick, butterthe bricks already laid togetherwith a small amount on both sidesof the brick to be laid. Gently pushthe brick into place ensuring thatmortar does not build up tosmudge the brick faces (fig 5.15c).To finish the joints between thebricks on edge, pull the jointeraway from the corner to leave aclean line and compact the mortarat the arris (fig 5.16). Finally, run amortar fillet between the tilecreasing and the brick-on-edgecapping if required (fig 5.17).

NOTE: The Brick DevelopmentAssociation does not consider thattile creasing will continue to be aneffective DPC in resisting thedownward flow of water over along period of time. A continuousDPC below the tile creasing,

Butter brickbeing laid

Direction of troweloverjoint to avoidsmudging

Spread mortar thinlyon all joint faces andlower brick into place

Jointer orpointing trowelmoved away fromcorner of brick

Mortar fillet betweenbrick-on-edge andtile creasing

Figure 5.17. Final fillet.

Figure 5.15a. Filling vertical joints. Figure 5.15b. Striking off mortar.

Figure 5.15c. The last brick.

Figure 5.16. Finishing joints.

KEY POINTS

■ Bed DPCs on fresh flat mortareither projecting or cut flushwith mortar joints.

■ Work out gauge to preventunnecessary and unsightly cutting.

■ Align ‘high’ copings along loweredge and ‘low’ copings alongupper edge.

■ Consider the ‘sight line’ beforefixing the lines and pins.

■ Fill all joints solidly as the workproceeds.

■ Remove excess mortar byrunning the trowel along theline of the joint to preventsmudging.

■ Keep checking gauge tomaintain an even joint size.

■ Maintain throat across jointsbetween coping units.

although not common practice, isstrongly recommended to ensureits continuing effectiveness. Brick-on-edge and tile creasing is not

considered be completely effectiveas a coping unless the tiles have acontinuous nib from which acontinuous throat is formed.

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CAVITY PARAPET WALLS 119

Too often parapet walls aredesigned or built so badlythat rain penetrates or thebrickwork cracks or suffersfrost or sulfate attack. Puttingthe faults right is usuallyexpensive and disruptive forthe occupants.

This section explains theprinciples of good design andconstruction by reference to themost common form of parapet,i.e. those projecting above flat orpitched roofs, although they arealso used elsewhere includingbridges.

High parapets provide a safetybarrier at the edge of roofs towhich people have ready access.They should be designed bystructural engineers to resiststrong winds and people leaningagainst them (fig 5.18).

Low parapets to flat andpitched roofs may be only theminimum height for practicalconstruction (figs 5.19 & 5.20).

Both faces of a brick parapetwall must be built to line, level,gauge and plumb and left cleanand jointed. But, in addition theymust be able to resist the verysevere exposure of the threesurfaces to wind-driven rain andextremes of temperature.

The following checklist ofoperations will help bricklayersavoid the most common faults.The typical examples illustratedare of facing brickwork cavityconstruction, as solid parapetsare not recommended in thesecircumstances, being more liableto rain penetration. Renderedparapets require furtherconsideration which is beyondthe scope of this section.

BUILDING OPERATIONS

DPC trays1 Build DPC trays into the innerleaf not less than 150 mm abovethe finished roof (figs 5.21a,b & c). Use only specified DPCsand in particular never polytheneor other low adhesion DPCswhich may cause a plane ofweakness and allow rainpenetration between the DPC and

5.2 CAVITY PARAPET WALLS

Figure 5.20. Low parapet walls to pitched roofs.

Figure 5.18. High parapet wall toaccessible flat roof.

Figure 5.19. Low parapet wallto flat roof.

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the mortar (see Section 4.3‘Damp-proof courses’).

2 Step cavity trays up or downto the outer leaf as instructed,by not less than 150 mm. If thecavity contains thermal insulationthe tray must step down to theoutside leaf to protect the top ofthe insulation which should belevel with the bottom of the tray(figs 5.21 a & b).

Trays should also be slopeddown to the outer leaf in highlyexposed conditions as otherwisewater may track across theunderside of the cavity trayafter penetrating under the DPC(fig 5.21c). Failure to achievegood adhesion by bedding theDPC on fresh mortar will increasethis risk.

3 Stepping trays down to theouter leaf increases the risk ofstaining below weep holesalthough the risk is not greatand is invariably preferable torain penetration. Proprietaryfibrous filter plugs are sometimespositioned in weep holes with theintention of reducing staining byfiltering solid particles from thedrained water. The risk of stainingcan also be reduced by clearingmortar droppings from the cavitytray before closing the cavity.

4 Bed DPC trays on fresh mortarfollowed by the next course assoon as possible to achieve goodadhesion between mortar andDPCs. DPCs should project5 mm, or be flush as instructed.Never position DPCs so that theedges are covered with mortaras this can cause spalling of themortar and brick edges as theDPC compresses under load(see Section 4.3 ‘Damp-proofcourses’). Figure 5.21. Typical alternative parapet details.

Figure 5.21a.

PC concrete coping

DPC bedded on fresh mortarRigid support

Clean mortar droppings from tray

Carry insulation up to underside ofcavity tray

Weep holes at minimum of 1 m centres

Min

imum

150

mm

Rooffinish

DPC bedded onfresh mortar (Seetext)

Modified standardbrick-on-edgedouble cant capping

Cavity insulation upto underside ofcavity tray

Weep holes atminimum of 1 m centres

Min

imum

150

mm

Rooffinish

DPC stepped down to inner leafonly if no insulation in cavity

BUTWeepholes

Risk of rain penetration alongunderside of tray (see text)

Min

imum

150

mm

Rooffinish

Figure 5.21c.

Figure 5.21b.

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5 Cavity trays in a parapet wallwill often have to drain awaylarge quantities of water, and ifthere are any poorly sealed jointssome water will leak into theinsulation and the inner leaf.

Joints, in long runs of cavitytrays (‘running laps’) or withpurpose-made return units, mustbe lapped by at least 100 mmand sealed (fig 5.22). Use eithera liquid adhesive or an adhesivetape as recommended by theDPC manufacturer.

Unless permanent proprietaryjoint-supports, usually ofpolypropylene, are specified,improvise a plywood off-cutto support the lap temporarilywhile the two portions arepressed together.

The use of preformed cavitytray units at corners and changesof level is simpler than cuttingand forming sheet DPC on site.

Metal flashings at abutments ofroof and parapet wallsThe purpose of metal flashings isto weather the junction betweenDPCs and roof finishes.

Unfortunately poor design and/orbuilding practice often result inrain penetration.

6 Flashings must be in the samejoint as DPCs and under them(fig 5.23a). If the flashing is overthe DPC (fig 5.23b) or in anotherjoint (fig 5.23c), rainwater maypenetrate.

Preformed internalreturn DPC unit sealedto cavity trays

Minimum100 mm sealedoverlap

Inner leaf

DPC

Flashing

Inner leaf

Flashing

DPC

Inner leaf

DPC

Flashing

Figure 5.23. Right and wrong ways of positioning DPCs and flashings.

Figure 5.23c. Flashing in course belowDPC – possible rain penetration.

Figure 5.23b. Flashing over DPC –possible rain penetration.Figure 5.23a. Flashing under DPC.

Figure 5.22. Sealing DPC trays and units where lapped.

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NOTE: If lead DPCs are in contactwith free lime from mortar forprolonged penods in very wetconditions, they should beprotected from corrosion by athick coat of bitumen paint onboth sides. However, the LeadSheet Association does notconsider such protectionnecessary for lead flashingstucked only 40–50 mm intomortar joints, since in suchconditions, relatively near thedrying surface, carbonation offree lime is rapid and there is saidto be no risk of corrosion.(1)

THERE ARE TWO BASICMETHODS OF INSTALLING

FLASHINGS

(1) Flashings are fixed intounfilled joints or chases left bythe bricklayer7 After bedding the DPC trayon fresh mortar, the bricklayersshould rake the green mortarfrom below the DPC, to a depthof 25 mm to leave room for theflashing to be inserted and fixedat a later date.

8 BUT it is very difficult to fill sucha thin joint with sealant (mortarwould be ineffective) and wedgingis virtually impossible (fig 5.24a).In practice the joint below theDPC should be at least 8 mmthick. Such a thick joint is normallyunacceptable in facework butthis can be overcome by cuttingrebates in the bricks on a masonrybench saw (fig 5.24b). Cutting achase into the finished brickwork,with an angle grinder, is possiblebut difficult.

9 When the flashing is fixed itshould be wedged every 450 mm,and a suitable backing material

inserted so as to leave the correctdepth for pointing with a sealantwhich is compatible with the DPCmaterial. Information on sealantsand backings should be obtainedfrom the manufacturer of theparticular sealant to be used.

Two-part and one-partpolysulfide-based sealantsshould be to the relevant BritishStandards.(2)(3)

Care should be taken whenfixing wedges, as brickwork lessthan 600 mm high may be lifted,particularly if the bond betweenthe mortar and DPC is weak.

10 If the joint is not raked out bythe bricklayer, the trade fixing theflashing is likely to destroy theedge of the DPC when choppingout the hardened mortar (fig 5.25).

(2) Flashings built-in by thebricklayer11 For this method, theLead Sheet Association(4)

recommends that flashingsare single welted and formedso that at least 50 mm restson the brickwork (fig 5.26).The DPC tray is bedded onfresh mortar followedimmediately by the nextcourse of bricks. The weltanchors the flashing in themortar and avoids the use oflead wedges and the risk oflifting brickwork as mentionedin 9 above.

Experience seems to suggestthat if the DPC is well bedded,the joint between it and alead flashing will remainweathertight.

Inner leaf

DPC

Flashing

Sealant

Inner leaf

DPC

Flashing

Sealant

Backing material and spacefor wedging at every 450 mm

Figure 5.24a. Difficult in practice.

Figure 5.24. Fixing a flashing – practicalconsiderations.

Figure 5.24b. Bricks rebated to providea wider joint and a more practicableoperation.

Figure 5.25. DPCremoved in error leads torain penetration.

Inner leaf

DPC cut backwhen choppingout mortar toreceive flashing

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Weep holes12 Form weep holes in verticalcross joints at a maximum of 1 mintervals in the course laid on thelower side of the tray. Leaveweep holes clear of debris andinsert filter plugs if specified.

Copings and cappings(see Section 5.1 for definitions)13 Clean mortar droppings anddebris from cavity trays toprevent debris being washedthrough the weep holes byrainwater penetrating thecavities and causing stains.

14 Bed the DPC on fresh mortarfor maximum adhesion and on arigid support across the cavity toprevent the DPC sagging into thecavity which will channelrainwater percolating throughthe coping or capping, into thecavity (fig 5.27). Bed the copingor capping immediately after theDPC to load the mortar joint andget the maximum adhesionbetween DPC, mortar and coping(see Section 5.1 ‘Copings andcappings’).

In Figure 5.21b a DPC isshown one course below thebrick-on-edge capping, ratherthan immediately below it, inorder to provide more weight andbetter adhesion and stability atthe joint containing the DPC. This

DPC may not be specified in avery low parapet if it is only one ortwo courses above the cavity tray.

Proprietary systems ofspecial interlocking bricks andincorporating a DPC have beendeveloped by several brickmanufacturers in order toprovide greater weight andstability. They should be builtstrictly in accordance with themanufacturers’ recommendations.

Mortar joints15 Fill all bed and cross jointssolidly with mortar and finishwith struck, weathered or buckethandle joints to maximise therain resistance of both sides ofthe parapet wall.

Movement joints16 Because parapet walls arehighly exposed to extremes oftemperature from both sun andwind and are not restrained bythe weight of any structureabove, movement joints will berequired at closer intervals thanin the main walls and must becarefully built (see Section 4.5‘Vertical movement joints’).

The right bricks17 Clay bricks used for copings,cappings and for parapet wallswhich are topped with cappingsrather than copings must befrost resistant (F). Calcium silicatebricks in cappings should be atleast class 4 (see Section 6.4‘Durability of brickwork’tables 6.1 & 6.3).

The right mortarIn most conditions only mortarmixes of designations M12 andM6 are suitable. Designation M4is acceptable only when there isa low risk of saturation, e.g. in alow parapet which has a coping.

Sulfate-resisting cement isrecommended, in order to resistsulfate attack where there is ahigh risk of saturation and whereclay bricks with Normal (S1) ratherthan Low (S2) levels of solublesalts as given in BS EN 771-1(5)

are used (see also Section 6.4‘Durability of brickwork’ table 6.1).

Some specifiers may requirethe use of additives such asstyrene butadiene to increasethe water resistance of themortar joint.

For more detailed guidanceand recommendations seesection 6.4 ‘Durability ofBrickwork’ and in particulartable 6.5 – Masonry condition F‘Unrendered parapets’.

DPC bedded onfresh mortar

Single weltedflashing

Inner leaf

50 mm minimum

Figure 5.26. Building-in a flashing.

Figure 5.27. Unsupported DPC sagsand forms path for water passing throughcracked mortar joints to enter cavity.

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References(1) ‘Rolled Lead Sheet – The Complete

Manual’ 2003. The Lead SheetAssociation.

(2) BS 4254:1983 ‘Specification fortwo-part polysulphide-basedsealants’.

(3) BS 5215:1986 ‘One-part gun-gradepolysulphide-based sealants’.

(4) Figures 5.23, 5.24, 5.25 and 5.26are based on diagrams in ‘RolledLead Sheet – The CompleteManual’ 2003.

(5) BS EN 771-1: 2003.

increasing use of structuralmasonry in recent yearsmeans that some arches willbe ‘structural’, supportingroof, floor and wall loads.In either case the eye isreadily attracted to the archform, and bricklayers needto take particular care withthe appearance. Additionalengineering requirementsmust be met when buildingstructural arches.

Although many brickmanufacturers supply sets ofvoussoirs ready to build into

arches, bricklayers who can setout arches and cut bricks toshape will be well respectedfor having a sound, broadlybased-knowledge of theircraft As such they will be indemand for the moreadvanced, high quality facingand structural brickworkwhich will be increasinglyrequired.

This section covers the basicskills required when buildingcurved arches. The building ofsoldier arches is described insection 5.5.

KEY POINTS

■ Check type of bricks are asspecified or recommended.

■ Check mortar mixes are asspecified or recommended.

■ Check if extra vertical movementjoints are required.

■ Bed all DPCs on fresh mortar.

■ Project DPCs at face or build-inflush.

■ Seal all laps in DPCs withadhesive or tape.

■ Generally bed copings andcappings on DPCs supportedover cavity.

5.3 CURVED ARCHES

The arch, developed early inthe history of masonryconstruction, elegantlytransfers loads from abovewall openings to abutmentseach side. The Romans builtarched viaducts andaqueducts, and in VictorianBritain arches proliferated forspectacular civil engineeringstructures as well as simplehouses (fig 5.28).

Today, most arches arebuilt into the outer leafof cavity walls and are‘self-supporting’. But the

Figure 5.28a. A 19th century brickviaduct.

Figure 5.28b. Victorian granary –Bristol.

Figure 5.28c. Victorian houses –Lichfield.

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CURVED ARCHES 125

ROUGH ARCHESRough arches are built fromstandard, parallel-sided brickswith wedge-shaped joints(fig 5.29). The larger the radiusthe less the joints taper.

Their use is normally confined tosemi-circular or segmental archesand is probably most acceptablewhen rugged softmud or stocktype bricks are used. Smooth,even-coloured bricks seldom lookwell with tapered joints.

Although the bricks need nopreparation it may be necessaryto discard a few which varyunacceptably in size from theremainder.

wide (fig 5.30). This method issatisfactory only with relativelysoft bricks. A masonry benchsaw is required to cut hard bricks(see Section 2.5 ‘Cutting bricks’).

The basic geometry necessaryto draw part of an axed arch fullsize, in order to make andtraverse a template for cuttingarch bricks, is described in textbooks such as Hodge’s ‘Brickworkfor apprentices’.(1)

Some brick manufacturers willprepare drawings giving thenumber, size and degree of taperof brick voussoirs for an archand the dimensions of the timberarch centre required to support itduring construction. Some will cutthe bricks to shape before delivery.

GAUGED ARCHESTraditionally, gauged arches werebuilt from bricks known as‘rubbers’ made from a fine,redburning clay, blended witha high percentage of fine sand.They were soft enough to cutand rub to shape and size onsite. Very fine joints of 1 mm orless were achieved using limeputty (fig 5.31).

A few manufacturers maketraditional ‘rubbers’ but they areexpensive and are used mainlyfor high quality restorationwork. Some manufacturers offer

bricks of a similar appearance,mechanically cut and sometimesrubbed to shape. Depending onthe type of brick, joints 2–3 mmthick, using lime putty made withsilver sand, may be achieved.

The craft of building gaugedbrickwork is fully described inGerard Lynch’s book ‘GaugedBrickwork.’(2)

TEMPORARY SUPPORTSAll brick arches need temporarysupport during construction(figs 5.32a & b). Both thetypes of arch centres illustratedcan be used many times.

Place the arch centres onfolding wedges and timberprops each side of openings.The folding wedges:

• give fine adjustment whenlevelling the arch centre.

• enable centres or turningpieces to be gently lowered(‘easing’ and ‘striking’)when the mortar joints havehardened i.e. after 28 days for‘structural’ arches and 14 daysfor ‘self-supporting’ arches.

Today, proprietary, permanent,metal arch support systems orreusable polystyrene are oftensupplied to site for use insteadof traditional timber centring(fig 5.32c).

PREPARATION• Raise the brickwork abutments

both sides of an arch to thelevel of the springing lineand place the arch centre orturning piece in position.

• For segmental arches, raisefurther courses of walling toform the skewback bearings

Figure 5.29. A rough two-ring semi-circular arch.

Figure 5.30. An axed cambered arch. Figure 5.31. A gauged segmental arch.

AXED ARCHESTraditionally, axed arches arebuilt from voussoirs fair cut onsite from standard bricks usinga lump hammer, bolster andscutch. The joints are parallelsided and nominally 10 mm

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(fig 5.32b), making use of a‘gun template’ to obtain thecorrect angle (see Section 5.9‘Tumbling-in courses’,figures 5.95 & 5.98 showinga gun template in use).

• Next plumb up from thestriking point to locate themidpoint of the key brickposition. With rough ringarches having two or moreseparate rings, the secondand subsequent even-numbered rings must have acentral joint, not a key brick.

CONSTRUCTING A ROUGHRINGED ARCH

• Mark the width of the keybrick in pencil on the archcentre and mark a jointallowance each side(fig 5.33).

• Using a flexible steel tape,measure down the curveof the intrados from thekey brick space or centrejoint to the springing lineand divide into a wholenumber of equal sized brickspaces including a joint

allowance which should beas small as possible.Otherwise the wedge-shapejoints become too wide atthe extrados.

In practice the minimum joint,using cement:sand mortars, isprobably 6 mm.

• Set the first arch brick at thespringing line on beddingmortar built up slightly thickerat the extrados in order toform a wedge-shaped joint(fig 5.34).

• Continue placingwedge-shaped beddingmortar on the arch brickpreviously laid in orderthat the bricks follow thecurve. Build up both sidesalternately so that thecentre is loaded evenly.

• Set arch bricks accuratelyto the pencil mark spacings,and square across the soffit(fig 5.34).

Springingline

Strikingpoint

Supportingposts

Foldingwedges

Springingline

Foldingwedges

From strikingpoint

Supporting posts

Skewback

Skewback

Figure 5.32c. Solidexpanded polystyrenecentre in use.

Figure 5.32b. Solid timber turning piece for a segmental arch in ahalf-brick leaf.

Figure 5.32a. Traditional open timberframework arch centre for a semi-circular arch.

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CURVED ARCHES 127

• Set bricks dry on the archcentre by bedding back andleaving a joint space forrepointing at a later date.Insert foam or wood stripsat the soffit (fig 5.34).

• Set the key brick in placeensuring that mortar is solidlypacked into these last two topjoints at the crown of the arch.

CONSTRUCTING AN AXEDSEGMENTAL ARCH

The following applies whetherpurpose-made mouldedarch bricks are supplied by amanufacturer or voussoirs havebeen cut on site by a bricklayerworking from a full-size drawingfrom which a cutting templatehas been made. See brickwork

textbooks for detailed procedureof setting out an axed arch,making and traversing a cuttingtemplate, e.g. Hodge.(1)

Set up a temporary archsupport as before and mark ontop, in pencil, the width of thekey brick (fig 5.35). The widthwill have been determined onan arch setting out drawingprepared either by the architect,brick manufacturer or by thebricklayer on site.

• Mark a joint space, shown onthe arch drawing, at each sideof this key brick space.

• Using dividers, mark out inpencil the required number ofspaces each side of the keybrick corresponding to thenumber of voussoirs on thearch drawing. Each spaceallows for a voussoir andone joint.

• Bed the first voussoir at thespringing of the arch andcheck joint alignment usinga piece of string fixed to thestriking point of the arch(fig 5.36). Continue beddingand checking voussoirs.Work alternately on eachside so as to load the turningpiece (arch centre) evenly.

• Keep soffit joints clear ofmortar for later repointingas previously described.

• Ensure voussoirs are squareon the soffit and follow pencilmarkings precisely.

• Constantly check face planealignment with straight edgeor line and pins as the archprogresses (fig 5.37).

• When it becomes impracticalto apply mortar to thepreviously laid brick, ‘butter’each voussoir evenly across thebedding surface before setting.

Springingline

Mark equal spacesfor remainingbricks and joints

Space for keybrick and joints

Set each brick squareacross soffit and thefront arris flush withthe arch centre

Set bricks on wedge-shapedbeds. Leave soffit jointsopen for repointing usingfoam strips

Arch centreplumbedaccurately

Figure 5.33. Marking out a rough ring arch on an arch centre.

Figure 5.34. Setting bricks accurately on plumbed centre.

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Complete key brick jointing in asimilar manner to that describedin section 5.1 ‘Copings andcappings’ figure 5.15.

MANUFACTURED ARCH SETS

Many brick manufacturers nowoffer to supply, to the client’srequirements, sets of purpose-

made arch bricks. They may besized to be built with nominal10 mm joints or, using limeputty, 2–3 mm joints to simulatetraditional gauged brickwork.Most manufacturers havecomputer-aided design (CAD)facilities to determine the exactsizes and numbers required.Enquiries should have been madewith manufacturers at an early

stage in the design process ifpurpose-made voussoirs ratherthan manufacturer’s standardsets are required.

BRITISH STANDARD ARCHBRICKS

BS 4729(3) specifies taperedheaders (type AR.1) andtapered stretchers (type AR.2)(figs 5.38a & b).

The alternative dimensions forthe smaller end of the wedges(D) are to suit semi-circulararches of four different spanswhich are multiples of wholenumbers of bricks. All thesedimensions are set out in Table 6of the Standard.

Space for key brickplus space for jointboth sides

Mark out equalspaces for voussoirsplus one joint beginningat space for key brick

From striking point

Work alternately from each side

Check line ofvoussoirs with stringfrom striking point

Constantly check faceplane with straightedge or line

Butter four facesthinly when placingkey brick

Figure 5.35. Marking brick spaces on a turning piece for a segmental arch.

Figure 5.36. Building axed segmental arch.

Figure 5.37. Completing segmental arch.

D

215

75

Bothendsfaced

D

102 75

Figure 5.38a. Tapered header typeAR.1 to BS 4729.

Figure 5.38b. Tapered stretcher typeAR.2 to BS 4729.

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CIRCULAR BULL’S-EYES 129

DAMP-PROOF TRAYS OVERARCHES

All features which bridge acavity, with the exception ofwall ties, must be protectedfrom water running downinside the cavity by aneffective cavity tray whichwill collect the water anddischarge it to the outside(see Sections 3.3 ‘Externalcavity walls’; 4.3 ‘Dampproofcourses’; 6.7 ‘Rain resistanceof cavity walls’).

Cavity trays overcurved arches are difficultto form on site where theslightest imperfection canlead to rain penetrationand expensive remedies.Experience suggests thatthese vital accessories aremost satisfactory whenthey are purpose-made byspecialists.

References(1) Hodge, J. C. (1971) ‘Brickwork for

apprentices’. London: EdwardArnold.

(2) Lynch, G. C. J. (1990) ‘Gaugedbrickwork – a technical

handbook’. Aldershot: GowerTechnical.

(3) BS 4729:2005 ‘Recommendationsfor dimensions of bricks(including those of special shape)’.

KEY POINTS

■ Use an accurate centre orturning piece.

■ Provide strong, properly bracedtemporary support that will notcollapse under the weight ofbricks and mortar duringconstruction.

■ Raise centre or turning piece upto the required springing line ofthe finished arch.

■ Always ensure that an archcentre is perfectly plumb on facebefore setting the arch bricks.

■ Always plumb up from thestriking point to locate thecentre of the key brick.

■ Pre-plan and pencil markpositions for all the arch bricksaround the centre beforestarting work.

■ Prevent mortar from gettingunder the arch bricks and ontothe temporary support whenbuilding an arch.

■ Keep soffit joints clear of mortarto simplify pointing later.

■ When building an arch frompurpose-made bricks or withaxed voussoirs always use alength of string fixed to thestriking point to checkalignment.

5.4 CIRCULAR BULL’S-EYES

Great care is required toconstruct truly circularbull’s-eye openings in brickwalls.

Vertical and horizontaldiameters of finishedopenings must be absolutelyequal for a satisfactoryappearance and for acircular window frame tofit the space.

A bull’s-eye consists oftwo identical semi-circulararches, but the method ofconstructing the lower half isquite different from turningthe upper half.

CRAFT TERMSTerms in italics are illustrated infig 5.39.

CONSTRUCTIONMost bull’s-eyes are of axedbrickwork formed bywedge-shaped bricks calledvoussoirs with parallel jointsbetween. Wedge-shaped jointsbetween uncut bricks in arough-ring bull’s eye aregenerally considered unsightly.

It is possible for a skilledbricklayer to set out an axedbull’s-eye, make a cutting

template and produce voussoirsby hand using a hammer,bolster and comb hammer.See section 5.3 ‘Curved arches’.Bench-mounted masonry sawswould be required to cut bothhard and perforated brickscleanly.

However, most brickmakerscan readily supply purpose-madetapered arch bricks providedthey are ordered in advanceof site requirements. Themajority of manufacturers havecomputer-aided design (CAD)facilities to determine the sizesof arch bricks.

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SETTING-OUTA bull’s-eye is set out with keybricks on both the horizontal andvertical centre lines which meansthat if the face depth is bondedeach quadrant must have an oddnumber of voussoirs between keybricks to avoid joints in adjacentvoussoirs coinciding (fig 5.39). Ifspecial shape bricks, type AR.2.1to BS 4729(1), were used to buildthis bull’s-eye it would require 50rather than 56 voussoirs as theextrados (outer curved surface)face dimension of the standardarch brick is 75 mm, being basedon the former culvert or 9-inchradial end arch brick.

BUILDING SEQUENCEBuilding a circular bull’s-eyebegins with the lower half or

invert arch using a trammel.No temporary supports areused as they are for the upperarch which is built in a similarway to a normal semi-circulararch.

Brickwork up to the horizontalcentre lineThe brick wall is built up to thehorizontal centre line of thebull‘s-eye, racking back fromthe extrados of the invert arch(fig 5.40).

The wall should be sufficientlyhigh to support the timberbeam from which the trammelwill swing. The brickwork mustbe accurately lined through andplumb on face so that theentire circumference of thebull’s-eye will align with thecompleted wall.

The trammelA 100 � 75 mm timber, orsimilar, is bedded temporarilyon the brickwork in lime:sandmortar, spanning the opening,and the striking point orcentre of the bull’s-eye ismarked. Weighting it withbricks ensures that it will notmove (fig 5.40).

The trammel is cut from asuitable batten, say 25 � 6 mm.The length from the centre nailto the point is the outer radius ofthe bull’s-eye plus a mortar joint.The trammel is nailed to thecentre point mark on the timberbeam and should swing freely(fig 5.40).

The invertThe invert is carefully cut to therequired semi-circular shape.

Horizontal

Ver

tical

diameter

diam

eter

Upper archkey brick

UPPER ARCH

Centre linekey brick

Verticalcentre line

Horizontalcentre line

INVERT ARCH

Striking point orcentre of bull‘s eye

Invert keybrick

Extrados

Intrados

Face depth

Always an odd numberof voussoirs betweenkey bricks

Figure 5.39. Some craftterms used in this section.

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CIRCULAR BULL’S-EYES 131

Each brick is temporarily placedin position using wood spacersnormally 10 mm thick, torepresent bed and cross joints(fig 5.41). The curve is markedwith a pencil held at the pointof the trammel. The bricks arecut to shape with a bolsterchisel or masonry bench sawas appropriate to the type ofbrick, and finally dressed to thecurve with a comb hammer.Some manufacturers of hardbricks will cut the end of bricksto the shape of the extradoswhen ‘green’ leaving thebricklayers to make a verticalcut to fit the bond pattern.They are then permanentlybedded in position,checking with the trammel(fig 5.41) as each cut brickis set until the inverthas been completed(see Sections 2.5 ‘Cuttingbricks’; 6.9 ‘Bricklaying toolsand equipment’).

As the bricks at the bottomof the invert usually requirelong tapering cuts the use ofmachine cutting may be theonly practicable method with

many types of bricks. A finalrub with a carborundum stonewill improve the curved shapeas each of these cut bricks isformed and ensure that thelower half of the bull’s-eye isneatly bedded.

Voussoirs in the invert archWithout disturbing the timberbeam, carefully remove thetrammel and drill an additionalhole 225 mm closer to thetrammel point. Re-fix the

trammel to the beam carefully.This can now be used to setthe voussoirs by swinging theinvert of the bull’s-eye. A stringline is fixed to the centre nailto check that each voussoirradiates from the centre point.Bed the bottom key brick,checking with trammel andstring line. The positions of thevoussoirs are pencil-markedaround the invert starting fromthe key brick using dividers andworking to left and right.

100 × 75 mm crosstimber bedded at levelof horizontal centre line

Half-jointbedding

Nail at striking point orcentre of bull‘s-eye

Cross timberweighted withbricks

Timber block

25 × 6 mm trammel

Line of extrados

Figure 5.40. Building brickwork up to horizontal centre line.

10 mm temporarywood spacers

Figure 5.41. Marking the curve before cutting.

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The voussoirs are bedded fromthe invert key brick alternatelyeither side until the invert arch iscomplete up to the horizontalcentre line. Constant checks ofthe face plane must be madeusing a level or straight edge(fig 5.42).

Voussoirs in the upper archThe upper half is built in a similarway to any semi-circular arch(see Section 5.3 ‘Curved arches).An arch centre is set up andwedged in position and a stringline fixed to the centre point nail(fig 5.43). Using a steel tapecheck that the vertical diameteris exactly the same as thehorizontal diameter.

The voussoir positions are setout with dividers and markedwith a pencil around the archcentre. Voussoirs are beddedusing the string line to ensurethat they radiate from thecentre point of the bull’s-eyeand the face-plane alignmentis checked with a level orother straight edge. Alignmentof the arch face with the wallface is aided with a line andpins set up along the face ofthe wall.

Before each voussoir isbedded a nominal 10 � 10 mmstrip of polystyrene or taperedwood is positioned to preventa build-up of mortar on thesoffit by forming recessed soffitjoints for subsequent repointingwith a matching mortar(see Section 5.3).

Brickwork above the horizontalcentre lineThe brickwork surrounding thearch is marked and cut withthe same care as that at the

String line to checkvoussoirs radiatingfrom the centre 1st hole22

5

Figure 5.42. Building voussoirs into invert arch.

Close lagged timber arch centreor solid expanded polystyrene

String line tocheck everyvoussoir radiatingfrom centrestriking point

Figure 5.43. Building voussoirs into upper arch on arch centre.

invert. Parallel nominal10 mm joints of even widthshould be maintainedbetween all voussoirs andaround the circumference ofthe bull’s-eye.

After an absolute minimum ofseven days and when the mortarhas set hard and sufficientbrickwork built above to stabilisethe arch, the timber centre isremoved by easing the wedgesand removing the struts and thesoffit is pointed to match thefacework mortar.

MARKING OUT CUT BRICKSSURROUNDING A SMALL

BULL’S-EYE – AN ALTERNATIVEMETHOD

A small diameter bull’s-eye ofsay 600 mm may be marked andcut using a circular template ofplywood or hardboard insteadof a trammel. The bricks are laidon a flat surface with spacing forjoints and the template placed ontop. The curve is then marked onthe bricks with a pencil, cuttingand setting the invert as before(fig 5.44).

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SOLDIER ARCHES 133

Reference(1) BS 4729:2005 ‘Recommendations


Alternatively, they may besupported by a simple steelangle which will show beneaththe arch or may be suspendedfrom an angle or bracketsabove by steel reinforcement.Reinforced soldier arches are builton temporary timber supports(head trees) which are removedwhen the mortar has cured(see Sections 4.6 ‘Reinforcedand post-tensioned brickwork’;4.7 ‘Brickwork on metal supportsystems’).

CONSTRUCTIONThis section describes the basicbricklaying operations forconstructing a soldier archsupported by a steel box lintel.

Selection of bricksBecause soldier arches areconspicuous features, the bricksfrom which they are to beconstructed should be carefullyselected to ensure that:

• they do not vary greatly inlength. Experience suggeststhat the difference in length ofthe shortest and longest bricksshould be no more than 3 mm.

• unacceptably bowed, twistedor chipped bricks are rejected.

Raising revealsAfter the lintel has been beddedin position, raise three coursesabove soffit level as a verticalextension of the reveals (fig 5.46).

Centrenail

Pencil

Trammel

Woodblock

Bricks laid out dryto gauge and bondon a flat surface

Figure 5.44. Alternative method with a small bull’s-eye.

KEY POINTS

■ Ensure bull’s-eye is a true circle.■ Weight timber beam firmly

so that it does not moveduring use.

■ Space voussoirs evenly.■ Use string line from striking

point to ensure voussoirsradiate correctly.

■ Use line and pins to keep faceof bull’s-eye lineable with thewall face.

5.5 SOLDIER ARCHES

A soldier arch is a course ofbricks set on end and havinga flat soffit (fig 5.45). It is nota structural arch form and so apermanent independentloadbearing support isprovided.

Soldier arches in the brick outerleaves of cavity walls are usuallysupported by a proprietary steellintel, the type depending on theloading, cavity widths and thethickness of the inner leaf.

Figure 5.45. A typicalsoldier arch.

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These will provide support for thefirst and subsequent arch bricksas they are set in position fromeach end.

Setting outMark in pencil on the steel lintel,a horizontal gauge for the bricksin the soldier course at intervalsof 75 mm from each end. If theopening is to standard gauge,there will be an extra 10 mm gapleft between the last two marks.If not, evenly adjust the marks sothat a whole number of brickswill fit (fig 5.46).

Fix two bricklayers’ lines toalign and level the top andbottom of the arch (fig 5.47).

Spread a mortar bed along thetoe of the lintel.

Butter the first brick solidly,taking great care not to smearthe face, slightly furrow themortar to assist joint compactionwhen tapping the brick plumb,and set in position at one end.Without moving your hand fromthe brick check its verticality witha boat level (fig 5.47). Becausethe eye is drawn to a soldier archevery brick must be perfectlyplumb.

Support each brick with onehand while tapping it plumb, sothat mortar suction is given achance to hold the brick steady.

To place the last brick, thinlybutter the bricks already laid andboth sides of the brick to be laid.Gently push the brick into placeensuring that mortar does notbuild up to smudge the brickfaces (fig 5.48).

Form weep holes by removingmortar from the lower third ofvertical cross joints at no morethan 1 m centres. Generally,there should be no less than twoover any opening. If required,

7575 75 75 75 75 75+

1075 75 75 75

75

Figure 5.48. Last brick set and weep holes formed.

Figure 5.46. Reveals raised and horizontalgauge marked in pencil on steel lintel.

Bricklayer lines topand bottom edgesof soldier arch

Figure 5.47. Bricklayer’s linesin position. Mortar bed spread.End bricks set and plumbed.

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DECORATIVE BRICKWORK 135

insert or build-in proprietarypreformed plastic ventilator/weepholes or fibrous filters at the faceof the joint.

POLYCHROMATIC BRICKWORKPolychromatic brickwork isbuilt from bricks of differentcolours in decorative featuresranging from simple bandcourses of contrasting colourto complex patterns or murals.Coloured mortars may be usedto match or contrast with thebricks.

COLOURED MORTARSTrial panels, to determine therequired mortar mix, shouldshow at least 100 brick faces,be in accordance with PAS70:2003(1) and reflect theform of the decorative

brickwork to be built. Themortar joints should be rakedand pointed with differentmixes which must be allowedto dry before inspection(see Section 1.1 ‘Referenceand sample panels’).

Repeatedly producing mortarto a consistent colour on sitecan be difficult and timeconsuming. Changing mixes,either deliberately or throughinaccurate measurement of thequantity of pigments, sand, limeand cement or changing thetype or source of sand and eventhe cement, can result in colourchanges in the mortar andpatchy brickwork.

Figure 5.49. Use of pistol bricks on asteel angle support.

Some other pointsPistol bricks may be supplied tosite for bedding on lintels andsteel angles in order to avoid athick bed joint (fig 5.49). Whensetting bricks on steel angles itmay be necessary to chip off therear arris to allow them to bedcorrectly.

When building on temporarytimber supports (head trees),bricks are laid dry, not bedded in

mortar. First, fix suitable lengthsof foam strips or wood on thetemporary support to keep thebottom of the soffit joints clearof mortar so that they can bepointed when the support isremoved (see Section 4.7‘Brickwork on metal supportsystems’).

Foam strips are better thanwood for preventing leakage ofwet mortar.

KEY POINTS

■ Bed lintel and raise reveals threecourses above the soffit.

■ Mark horizontal gauge ensuringthat joints are equal.

■ Fix a bricklayer’s line top andbottom to align and plumb thefaces.

■ Select straight, undamagedbricks of a similar length.

■ Plumb the side of each brick asit is set in position.

■ Keep the faces of bricks cleanwhen buttering and finishing thejoints.

5.6 DECORATIVE BRICKWORK

Simple brickwork in half orquarter bond often providesall the colour, texture andpattern that is required.But sometimes it is enrichedby the use of differentcoloured bricks; modellingthe surface with projectingand recessed bricks;bedding bricks vertically orat an angle to the normalhorizontal bedding patternor using bricks of specialshapes.

The basic techniquesdescribed in this section canbe adapted by skilledbricklayers to build a varietyof decorative brickwork.

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Consistent jointing techniquesare necessary. For example, if themortar joints are too wet whenfinished by ironing or tooling, the

fines are brought to the surfaceso that the joint dries a lightercolour (see also Sections 2.8‘Pointing and jointing’; 6.6‘Appearance’ especially underheading 14 ‘Maintain aconsistent jointing technique’).

Suppliers of ready-mixedlime:sand (coarse stuff) providecolour charts and consistentmixes. If coarse stuff is usedit is still necessary to measureaccurately the amount of cementadded on site.

DIAPER WORKMany different diaper patternscan be created by coloured,projecting or recessed bricks(fig 5.50).

If different coloured mortarsare specified it is generallypreferable to use one mortarthroughout and rake theappropriate joints to a depthof 12–15 mm and point withcoloured mortar. Using twodifferent coloured mortars isdifficult, requiring two trowelsand two spot boards.

When building-in projectingbricks take particular care with line,level and plumb (fig 5.51). See also‘Projecting bricks’ on page 143.

BAND COURSESBricks supplied for band courses(fig 5.52) may have a differentaverage length from other bricksin the wall. Generally, set outall courses to the co-ordinatingdimensions of the bricks(225 mm for standard bricksin stretcher bond) by tighteningor opening vertical joints asnecessary and plumbing everyfourth or fifth perpend (seeSection 2.4 ‘Vertical perpends’).

Soldier coursesSoldier courses consist of bricksset on end showing stretcherfaces. The bricks should beselected, either by thebrickmaker or on site, to have aclose tolerance about the meanlength, typically �1.5 mm.

For greatest accuracy lay to aline. But a line secured to freshlylaid soldier bricks may pull them

Plumbprojectingbricks

Plumb diaper pattern on elevation

Depth gauge usedfor consistency

Figure 5.50a. Diaper pattern in quarterbond.

Figure 5.50b. Flamboyant Victorianbrickwork based on diaper pattern.

Figure 5.50c. Modern version in half bond. Figure 5.51. Vertical control of diaper work.

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out of plumb when pulled taut.To avoid this:

• Preferably build ‘Dead Men’ atthe ends or corners to securethe line and build the soldiercourse between (fig 5.53),then replace each ‘Dead Man’with three soldier bricks.

• Alternatively, construct thecorners in the traditionalmanner (see Section 2.3 ‘Line,level and plumb’) but do notrun out on the level morethan nine or ten soldier bricksas they are very difficult tokeep to line level and plumbbecause of the small bed area.

The eye is readily attracted tosoldier courses so take extra careto set the bricks plumb. As ageneral rule plumb every thirdsoldier with a boat level(fig 5.53). Butter the soldierbrick to be laid, not the faceof the last brick laid. In additionensure that the top of thecourse lines through. Forcomments on laying the lastbrick at the centre (see Section5.1 ‘Copings and cappings’figure 5.15 and section 5.5‘Soldier arches’).

Alternative methods ofreturning soldier courses areshown in fig 5.54. Note thatfigs 5.54a & b do not allow, onadjacent return walls, the samerelationship between the verticalcross joints in the soldier coursesand those in the course below.Architects sometimes requirevertical cross joints in a soldiercourse to coincide with those inthe course below, even thoughbricklayers are usually taught toavoid this.

Bricklayers may be requiredto build-in special ties to restrainthe smaller return bricks such as

that in fig 5.54a as they may bevulnerable to displacement bylateral movement of walls atthe corners.

HERRINGBONE BONDThere are six main types ofherringbone bond (fig 5.55).They are usually built as a panelsurrounded by normal half orquarter bonded brickwork, orbetween window openings.Setting out and building singlevertical herringbone bond isdescribed in some detail belowas an example. Brief commentsare made on other herringbonebonds.

Building single verticalherringbone bondBuild the surrounding brickworkaccurately to the correct height,level, plumb and gauge (fig 5.56).Ensure that the tops of thereveals are at the same level.Keep the opening width constantfor the whole height. This is bestdone with a pinch rod rather thanrelying only on keeping thereveals plumb.

Figure 5.52a. Bold use of band coursesin contrasting colours.

Figure 5.52b. Subtle use of bandcourses in snapped headers.

Dead Man

Plumb everythird soldierbrick

Position offirst line

Position ofsecond line

Figure 5.53. Use of ‘Dead Man’ to secure lines and plumbing soldier bricks.

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Setting-out and cuttingTransfer a full-size outline of theopening on to a suitable board(fig 5.57). Deduct 20 mm (the

total thickness of the 10 mmjoints at each reveal) from thelength and 10 mm from theheight to allow for the first bed

joint. Do not deduct 10 mm forthe joint at the top of the panelas the top of the herringbonepanel will be level with the topbricks of the reveals.

On the board, mark horizontaland vertical centre lines and linesat 45° to them through the centrepoint. This gives the position ofthe first bricks to be placed in thesetting-out process (fig 5.57).

Starting with two bricks(fig 5.57), place all the bricksdry and accurately on the board(fig 5.58). Any inaccuracy atthis stage will be reflected inthe built panel.

Next, transfer the outline ofthe board to the bottom andtwo sides of the dry bricks andcut the bricks to shape.

Bricks for decorative work arebest cut on a masonry bench

a. Standard special SD.1b. Standard special SD.2

Figure 5.54. Alternative methodsof returning soldier courses.

c. Standard special BD1.3

d. Standard bricks stack bonded e. Bonded corner

a. Vertical herringbone. b. Double verticalherringbone.

c. Horizontal herringbone.

d. Double horizontalherringbone.

e. Diagonal herringbone. f. Double diagonalherringbone.

Figure 5.55. Types of herringbone bond.

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saw. If it is necessary to cut anacute angle by hand, use a sharpbolster and first cut the bricksquare and then trim the angle tominimise the risk of the ‘point’breaking off. When cutting byhand, rest the brick on a bed ofsand or a pad of old carpet toavoid breaking the bricks (seeSection 2.5 ‘Cutting bricks’).

ConstructionAfter cutting the bricks to shape,place a gauge rod (cut to thewidth of the opening) along thebottom of the dry panel andmark the position of the cutbricks. Use the gauge rod as atemplate to position the bricks inthe first course.

The laying of herringbonebond must be controlled at anangle of 45°. Traditionally a ‘boatlevel’ and 45° set square wereused, but ‘boat levels’ are nowavailable with adjustable vials(fig 5.59). As the vials must beaccurate the levels should beobtained from a reputablemanufacturer. Run a level line tocontrol the top of each course.

Lay the last row temporarilyand mark them with a chalk line,level with the top of the reveals,and cut accurately.

Ensure mortar is of the rightconsistency to avoid stainingfrom wet mortars and so that thebricks can be gently ‘rubbed’ intoposition. Tapping or knockingdown bricks is likely to disturbthe work below far more inangled brickwork than inhorizontal courses.

Double vertical herringbone bondIn order to ‘centre’ the pattern,set the centre bricks in relationto the centre lines as shown(fig 5.60).

Tops of revealsto be level

Pinch rod foraccuracy

Length 910 mm

Hei

ght

675

mm

890 mm

665

mm

Perpendicular centre line

Horizontalcentre line

45°

45°

45°

Bricks at topto be cutonly afterbrickworkbelow is builtin place

Bricks atboth sidesand bottommarked forcutting

Figure 5.58. Bricks set-out dry and marked for cutting.

Figure 5.56. Opening to receive herringbone brickwork.

Figure 5.57. Setting-out board.

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Horizontal and double horizontalherringbone bondSetting-out and construction areas for the vertical bonds exceptthat the direction of the bondsis horizontal rather than vertical(figs 5.55c & d).

Diagonal and double diagonalherringbone bondThese bonds have approximatelyonly a third as many cuts as thehorizontal and vertical forms.Because the pattern aligns withthe main brick courses it can bebuilt at the same time, thusavoiding the lengthy setting-outprocess (figs 5.55e & f ).

BASKET WEAVE BONDBasket weave is usually formedwith three stretchers stackbonded and three ‘soldiers’laid adjacent (fig 5.61a).

Unlike horizontal and verticalherringbone bond, basket weavedoes not need to be set out dry,and no cutting is required, butthe opening must be kept tobrick sizes. Because level andplumb are critical, a boat levelshould be used on each brick as

Bricklayer‘s line tocontrol level of thetops of courses

Alternative methodsof checking 45° angle

‘Dummy’ starterfor setting-out

Figure 5.59. Constructing a single vertical herringbone panel.

Figure 5.60. Setting-out centre bricks for a double vertical herringbone panel.

a. Basket weave b. Diagonal basket weave c. Alternative diagonal basket weave

Figure 5.61. Basket weave bonds.

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well as checking for level andgauge by the line.

Diagonal basket weave bondBeing at 45°, diagonal basketweave bond (fig 5.61b) doesrequire setting-out and specialconstruction as described forvertical and horizontalherringbone bond.

Setting-out starts at the centreso that the complete panel issymmetrical. The centre of themiddle brick can be positionedat the centre of a square as aguide for setting-out with the45° lines passing directlythrough the centre (fig 5.61b).Alternatively, the maincontinuous joints can be set outto form an ‘X’ through the centreof a square panel (fig 5.61c).

INTERLACING BONDInterlacing bond, sometimesreferred to as ‘pierced panelling’,has 1/3 brick cuts left open andhas been used for garden walls(fig 5.62a).

The panel consists of wholebricks laid vertically andhorizontally, with 2/3 bricks toachieve the interlacing effect.

During construction lay the 1/3cut bricks in sand. Remove themwhen the mortar has set hard.

Alternatively the 1/3 cuts canbe bricks of contrasting colourlaid in mortar. The panel followsbrick courses and can be laid aswork proceeds, but ensure thevertical pattern is kept plumb asthis will be the ‘line of sight’.

Diagonal interlacing bondInterlacing bond (fig 5.62b)cannot be built as a pierced panel.As with all panels with 45° bonds,much cutting is required.

DOG TOOTHINGThere are two basic forms ofdog toothing. In both, twofaces are set at 45° to the lineof the wall face (figs 5.63a & b).In one, each arris betweenthe two faces projects 72 mmfrom the face of the wall andin the other they are flush withthe wall, forming a recessedfeature.

Building projecting dog toothingLay the first brick ‘dry’ onthe wall, mark and cut itaccurately for use as a templatefor the remaining bricks(fig 5.64a).

A line should be positioned atthe top of the arris to control theprojection (fig 5.64b).

Place a 1.2 m spirit level alongthe underside of the string courseto ensure that the ‘line of sight’is maintained. Level the coursefrom back to front regularly(figs 5.64c & d).

Set-out the corner detailsfirst and then set-out the bondover the whole length. Openor tighten the vertical jointsas necessary because it is notpossible to introduce cuts. Linethe cut surface of each dog toothbrick with the inside face of theexternal leaf to maintain the 45°angle. But check it with a bevel.

a. Interlacing bond b. Diagonal interlacing bond

Figure 5.62. Interlacing bonds.

Figure 5.63a. A dog tooth course ofblue bricks in a wall of London stocks.

Figure 5.63b. A recessed dog toothcourse with a dentil course below – bytrainees at West Kent College.

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Building recessed dog toothingProceed in a similar manner asdescribed for projecting dogtoothing but position the lineon the face line of the wall.As this makes contact withthe arrises only, check the levelof the dog toothing everythree or four bricks with a spiritlevel.

See the paragraph headed‘Projecting bricks’ on page 143.

DENTIL COURSESA dentil course consists of aregular pattern of projectingheaders cut to project 28 mm.In cavity walls, the cut is flushwith the inner face of the outerleaf (fig 5.65). The feature isfinished with a course ofstretchers laid centrally over theheaders either flush or projectinga further 28 mm.

The projecting headers shouldbe placed to avoid a straight jointwith the course below. See theparagraph headed ‘Projectingbricks’ below.

MURALSBricklayers are required to workto detailed drawings for theposition and colour of each brickin polychromatic murals such asthat in fig 5.66.

PROJECTING BRICKSWhen bricks are being specifiedfor decorative brickwork thatincludes projecting bricks,consideration should be givento the following:

• Perforations and frogs may beexposed to view and theweather, in which case solid

OffcutTemplatebrick Two lines-width of outer

leaf apart

Join ends for 45° line

Position of corner brick

Position brick at 45° andmark and cut as template

Brickwork outer leaf

Position ofbricklayer‘s line

Position ofbricklayer‘s line

Long level tounderside

Dog toothcourse

Boat level

Position ofbricklayer‘sline

Long level

Figure 5.64d. Vertical section throughdog tooth course.

Figure 5.64c. Elevation of dog tooth course.

Figure 5.64b. Plan of dog tooth course.

Figure 5.64a. Marking 45° line on top of outer leaf – positioning and cutting template brick.

Figure 5.64. Constructing a dog tooth course.

Figure 5.65. A dentilcourse.

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CURVED BRICKWORK 143

bricks will generally beadvisable.

• Exposed bed surfaces ofstandard bricks will usually bedifferent in appearance fromthe normal face but can bematched as a special

requirement as type BD.1.3 toBS 4729(2).

• For some types of bricks,opposite stretcher andheader surfaces differ inappearance. Check whetherpurpose-made bricks withtwo faced stretchers havebeen provided, e.g. forthe return of a dog toothcourse.

Figure 5.66. A mural depicting a steelworker – in Sheffield.

KEY POINTS

Because decorative brickwork is eyecatching, pay particular attention tothe following:

■ Bricks with close dimensionaltolerances are advisable formost decorative brickwork. Ifspecified, ensure that only suchbricks are used.

■ General accuracy of plumb lineand gauge.

■ Plumb of soldier bricks.■ Accuracy of projections

and overhangs – they castshadows.

■ Consistency of mortar to allowrubbing down of diagonalbrickwork.

■ Accurate control of bricks at45° angles.

■ Neat and consistent jointing andpointing.

■ Neat and accurate cutting ofbricks.

■ Cut dog tooth bricks accuratelyso as not to protrude into thecavity.

■ Protect finished work,especially projections, as workproceeds.

• Exposed projecting bricksshould be specified frostresistant.

References(1) BSI PAS 70-2003 ‘HD clay

bricks – Guide to appearanceand site-measured dimensionsand tolerances’.

(2) BS 4729:2005 ‘Recommendationsfor dimensions of bricks (includingthose of special shape)’.

5.7 CURVED BRICKWORK

When building straight wallsto line, level, gauge andplumb, the most importantitems in a bricklayer’s tool kitare ‘line and pins’. But asthese cannot be used forcurved walls, bricklayersadopt other methods asdescribed in this section.

Figure 5.67. Timber template approx. 1.2 m to check alignmentof curved course.

ALIGNMENT WITH TEMPLATESAlignment is most commonlychecked with a curved templatemade from a fiat board about1200 mm long (fig 5.67).

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SETTING-OUTStraight walls are set-out usingstring lines between foundationprofiles.

To set out curved walls, findfrom the drawings, and locateon site, the position of thestriking point (A) and theradius of curvature (B)(fig 5.68).

The builder will dig curvedfoundation trenches and placeconcrete on which the bricklayerscan set-out the curved walling.

TRAMMEL AND PLUMBUsing a trammel (radius rod) andspirit plumb rule, plumb downinto the trench and mark points

in a thin mortar screed (fig 5.69).Use a template to join the pointsand mark a complete curvelocating the face side of thewhole wall (fig 5.70).

BONDINGWalls that are curved on plancan be built from straight bricksby forming wedge-shaped mortarcross joints. A stretcher bondedconvex curved half-brick leaf(102 mm thick) can be built to adiameter as little as 3 m withoutthe need to cut the back cornersand to give an acceptable crossjoint on the face.

For thicker walls of various facebonds, bricklayers should ‘strike’the radius of curvature on a flatsurface and lay out the bricks ‘dry’around the curved line. This willindicate the amount of cuttingrequired, widths of cross joints onthe face and whether Flemish orHeader bond is possible where asmall radius is required.

For the best appearance,curved walls are built withcurved bricks known as ‘radials’(fig 5.71). Six standard radialheaders and six standard radialstretchers, specified in BS 4729(1),give convex walls with six idealouter radii from 450 mm to5.4 m. These are summarisedin table 5.1.

The use of radial bricks shouldallow cross joints to have parallelsides rather than be wedgeshaped. Further detailedinformation on radial bricksand their use is given in tablesin BS 4729(1) and the BrickDevelopment Association’spublication, ‘The design of curvedbrickwork’(2). The latter alsoincludes information on the useof straight bricks in curved walls.

AB

A

B

From nail to point of trammelis the radius of curvature tothe face side of wall

Figure 5.68. Timber peg at striking point A, and trammel to set out radius of curvature Bas found from drawings.

Thinmortarscreed

Stout timberpeg at strikingpoint

Radius ofcurvature

Keep trammel horizontalwhen plumbing down

Curved stripfoundation Template

Figure 5.69. Trammeling and plumbingdown position of curve.

Figure 5.70. Completing line of curve withtemplate.

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CURVED BRICKWORK 145

A BASIC METHOD OFCONSTRUCTION

First courseCarefully bed the first course ofbricks to the line of the radiusmarked in the screed. Use thetrammel and spirit plumb rule to

check the alignment. Any ‘kinks’in the first course will becontinued to the full height ofthe wall.

Level-in bricks using a straightedge and spirit level (fig 5.72).

Plumbing points and templatesAs there are no quoins either endof a curved wall, establishplumbing points at about 1200mm intervals. Make templatesany convenient length, 1200 mmis a comfortable size to supportin one hand while holding atrowel in the other. Longertemplates require fewerplumbing points.

Like quoins in straight walls,plumbing points control plumb,gauge and alignment for the fullwall height. Levelling of coursesalso takes place betweenplumbing points because that iswhere the gauge is controlled(figs 5.72 & 5.73).

Straight bricks and templatesThe whole length of the faces ofstraight bricks cannot follow a

curved template. Instead, in aconvex face, both arrises of allbricks must touch the template(fig 5.74).

For a concave face where areverse template is used(fig 5.75), the centre of theface of each brick must touchthe template, and the arrisesshould be equidistant from thetemplate.

Radial bricks and templatesWith radial bricks manufacturedto suit the particular curvatureof a wall, the whole face ofeach brick should touch thetemplate.

TABLE 5.1 Standard radial bricks – to BS 4729

Type no. Dimension ‘D’ Ideal outer radius No. of bricks in quadrant

RD.1.1 52 450 6RD.1.2 70 675 9RD.1.3 80 900 12RD.1.4 89 1350 18RD.1.5 97 2250 30RD.1.6 103 5400 72RD.2.1 172 450 3RD.2.2 190 675 41/2RD.2.3 199 900 6RD.2.4 208 1350 9RD.2.5 215 2250 15RD.2.6 221 5400 36

NOTE: This table consists of information selected from BS 4729 and should be read inconjunction with fig 5.71 of this section.

‘D’ (seetable 5.1)

‘D’ (seetable 5.1)

RD.1 Radial header

RD.2 Radial stretcher

65C

65C

A–215

A–226

B–108

B–102

Figure 5.71. Standard radial bricks toBS 4729.

Figure 5.72. 1.2 m straight edge reachesbetween plumbing points.

Plumbfacework

Lead bricks atplumbing point

Checkperpends

Check gauge atplumbing points

Figure 5.73. Bedding lead bricks.

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ANOTHER METHOD OFCONSTRUCTION

Where space allows, thecurvature of a wall can becontrolled using a trammel only.A template is not required.

A steel rod is fixed vertically(fig 5.76) instead of a woodenpeg (fig 5.68).

A trammel is used to check theposition and alignment of everybrick.

Temporarily concrete-in thesteel rod at least one day before

it is to be used and take care it istruly plumb and rigidly fixed.

At the completion of eachcourse raise the trammel up thesteel rod by the height of onecourse. Support the trammel withan elastic band wound round thesteel rod and rolled up for eachcourse.

This simple device supports thetrammel horizontally, and allowsthe radius dimension to the faceside of each course to bechecked as it is laid.

Levelling between plumbingpoints must still be carried out asin fig 5.72.

Verticality and gauge muststill be checked at plumbingpoints as in fig 5.73 e.g. at 1 mintervals round thecircumference.

THE NEED FOR CARE ANDATTENTION

To form a ‘sweet curve’ requiresgreat care and attention to makecourses truly level and to keepplumbing points accurate. Checkthat both ends of every bricktouch the straight edge whenlevelling.

Curved brickwork will be asgood as well-laid straightwalling only if very great careis taken with plumbing pointsand templates.

References(1) BS 4729:2005 ‘Recommendations

for Dimensions of bricks (includingthose of special shape)’.

(2) Hammett and Morton, ‘Thedesign of curved brickwork’.The Brick DevelopmentAssociation.

Both arrises of straightbricks must touch template

and both arrisesequidistant fromtemplate

Centres of straightbricks touch thetemplate

Figure 5.74. Checking alignment of convex facewith template.

Figure 5.75. Checking alignment of concave face withreverse template.

Steel rod must beas high as walland plumb

Elastic bandundertrammel

Trammelheld level

Face side

Temporaryconcrete

Figure 5.76. Controlling curvature of eachcourse with a trammel from a centre rod.

KEY POINTS

■ Locate exact position of strikingpoint.

■ Accurately shape templates tothe correct radius.

■ Set out carefully, keepingtrammel horizontal.

■ Lay out bricks ‘dry’ around thecurve to check the size of crossjoints.

■ Make distances betweenplumbing points equal to lengthof template.

■ Plumb down from datums tobegin gauging at each plumbingpoint (see Section 2.2).

■ Continually check plumband gauge, only at plumbingpoints.

■ Pencil plumb perpends atevery plumbing point(see Section 2.4).

■ Level bricks betweenplumbing points with great care.

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CORBELLING 147

A corbel, in general buildingterms, is an isolated orcontinuous feature builtinto and projecting from theface of a wall to supportwalling, in front of the mainwall, or roof trusses, floorsor beams.

The unusual stone corbel inan arcade at Queen’s CollegeCambridge (fig 5.77) and theaccompanying diagram (fig5.78) illustrate the way acorbel works in principle. Thetendency for the load ‘A’,supported by the projectingportion, to rotate the corbelanticlockwise iscounterbalanced by load ‘C’,from the brickwork above,acting clockwise to preventtension and crackingdeveloping at ‘B’ and possiblefailure of the corbel to carryits load.

TRADITIONAL BRICKCORBELLING

Traditionally, the mainpurpose of corbelling was toprovide structural support butthe opportunity was oftentaken to enrich the structurewith mouldings or carvings. Brickcorbelling may consist either ofsingle point supports, such as adrop corbel, or of continuousoversailing courses eachprojecting beyond the one below.

The following two examplesare included solely to describethe basic bricklaying skills neededto build traditional corbelling andfrom which the skills to build

modern examples can bedeveloped.

Simple structural brickcorbelling must not exceed thelimits recommended in theMasonry Code of Practice(1)

(fig 5.79), unless designed by astructural engineer.

PREPARING TO BUILD A DROPCORBEL

The corbel in this example isto support a two-brickwide attached pier, projecting

from the main wall by thelength of one brick (fig 5.80).

The position of the pier,the bonding and perpendsshould have been plannedat ground level beforebricklaying began.

• The corbelling begins threecourses below the full widthand projection of theattached pier. Each courseprojects a quarter of a brick,both parallel with and at

5.8 CORBELLING

Figure 5.77. Anunusual use of a stonecorbel at Queen’sCollege, Cambridge.

Figure 5.78.Demonstrating theprinciple of the corbel.

CA

Corbel stone setin brickwork

B

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a right angle to the faceof the wall.

• The first header is on thecentre line projecting by aquarter-brick (fig 5.81a).

• The second course of twoheaders projects all round by afurther quarter-brick or a totalof a half-brick (fig 5.81b).

• The third course of threeheaders projects a total ofthree-quarters of a brick(fig 5.81c).

• The final course is twostretchers wide to beginthe English bond in the pier(fig 5.81d).

Keeping projections even andplumbThe projecting corbels must beequal, level, straight and parallel.A number of techniques fordoing this are described below.

Making a corbelling template• Take a piece of hardboard

exactly 225 mm wide with endAC cut square to the sides.Mark off 300 mm (AB) downone side. Join BC (fig 5.82).

• Divide AB into the four corbelcourses including bed joints,i.e. 75 mm.

No diminutionin thickness onopposite sideof corbel

TMaximumcorbel T/3 Maximum

corbel T/3

Sectionthroughsolidwalling

Sectionthroughcavitywalling

TWall tie

Figure 5.79. Recommended extent of brick corbelling.

Figure 5.80. An example ofa drop corbel.

a. First course.

b. Second course.

c. Third course.

d. Fourth course.

Figure 5.81. Plans for corbel courses.

225A

B

C

300

7575

7575

Line ofcutReversetemplate

Waste

Figure 5.82. Marking out and cuttingreverse template.

Reversetemplate

Finaltemplate

A

B

C

Figure 5.83. Marking outline of finaltemplate.

• Project these square from ABto intersect line BC. Fromthese intersections draw linessquare to AC and projectingbelow line BC.

• Cut along the stepped linebelow and to the right of BC.You now have an accurateprofile of the proposed brickcorbels. Use this reversetemplate to transfer the marksto a sheet of plywood and thencut the final template (fig 5.83).

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CORBELLING 149

• Use a straight edge to aligncorbelling at each end of thepier face as well as the sidereturns (fig 5.86). Line throughthe face as each course is laid.

• Level and line-in the soffit ofeach corbel course (fig 5.87).

• As a double check place astraight edge along the faceof each corbel course andmeasure its distance from thewall at each end. They shouldbe the same (fig 5.88).

Template

Figure 5.84. Using a template with aplumb level.

Figure 5.86. Aligning corbels with astraight edge.

Figure 5.85. Keeping corbels square with wall.

Figure 5.87. Levelling corbel courses.

Straightedge

Figure 5.88. Making a double check.

The template is used witha plumb level to check theprofile of the corbelling(fig 5.84).

KEEPING CORBELS SQUARE TOTHE WALL, ALIGNED AND

LEVEL• Use a square held against the

wall to check each course(fig 5.85).

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BUILDING THE DROPCORBELLED COURSES

• Raise the main wall to thebeginning of the corbel orcorbels. Mark the position ofthe corbel with a headerplaced dry allowing a joint ateach side (fig 5.89a).

• Rack back from the corbelboth sides. Bed the firstcorbel brick and bed a cutbrick behind it (fig 5.89b).

• Mark the position of thesecond corbel course with astretcher placed dry(fig 5.89c).

• Rack back and bed a stretcheron the cut brick trapping thecorbel brick below. This is toprovide back-weight to ‘taildown’ the corbelled bricksand provide a counterbalance to preventoverturning (fig 5.89d).

• Bed second course of twoheaders (fig 5.89e), levellingunderside as figure 5.87 andcheck for square as figure 5.85.

• Build the third and fourthcorbel courses similarly,bedding cut bricks behindand solidly ‘tailing down’each course of corbelling.

• When bedding corbel bricks,allow them to tilt a little‘backwards’ or ‘inwards’ tothe main wall, for as eachsuccessive course is tappedinto place the bricks in thecourse below will settle slightlyuntil level (figs 5.90a & b).

The two stretchers in the fourthcorbel course may well requiretemporary support by a timberbatten until firmly ‘tailed down’by subsequent courses.

Align and level the soffits, notthe top of each brick course asis normal. The eye is alwaysdrawn to projecting featuresand will readily notice anyunevennesss.

If perforated bricks are used inthe main wall, check, beforebeginning work, whetherpurpose-made solid versionshave been ordered so that

perforations will not be visiblefrom below. Also, if the type ofbrick used has bed surfacesmarkedly different from thefaced surfaces, a StandardSpecial BD 1.3(2) which has onebed surface faced may havebeen ordered, or even apurpose-made special that hasboth stretcher surfaces faced.

Frogged bricks should ofcourse be laid frogs uppermost.

WALLING LENGTHS OFCORBELLING

Total projection from the wallface, projection of each course,setting-out, use of template andchecking for squareness andalignment are carried out asdescribed for the drop corbel.

An additional requirement isthe necessary use of line and pinsfor running in each course ofcorbelled brickwork. The linemust be secured to the bottomFigure 5.89. Building the corbel.

a.

Tilt inwards

b.

Brick settled inlevel position ascourses aboveare levelled

Figure 5.90. Tilting corbel bricks inward.

a.

b.

c.

d.

e.

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TUMBLING-IN COURSES 151

arris of the corner brick at eachend of the course. As this can befiddly, it may be worth using thesmall metal or plastic cornerblocks or shoes which areavailable (fig 5.91).

BUILDING MODERNCORBELLING

In many modern buildings, steel orconcrete frames support andrestrain the external cladding ofbricks and blocks. The outer leavesof brickwork often include acorbel-like shape purely as anembellishment. It does not supportany load, and indeed is itselfinvariably supported and tied backto the structural frame by a systemof steel angles, ties and brackets.This technique is described morefully in section 4.7.

Here, bricklayers cannot usethe technique of ‘tailing down’and often raise only a fewcourses and wait for the mortarto set and the ties to be effectivebefore raising the work further.


for use of masonry’, cl. 5.3.6.(2) BS 4729:2005 ‘Recommendations


used in the past to reduce thewidth of an external chimneybreast to that of the chimneyand to reduce the projectionof attached piers (figs 5.92 &5.93).

The skills required shouldnot be lost by neglect merely

because the feature has beenlittle used in recent years.Architects might moreoften find tumbling-inappropriate if they wereaware that bricklayers stillhave the necessary knowledgeand skill.

Wall face

Corbel line

Figure 5.91. Walling a length of corbelling.

KEY POINTS

■ Plan position of pier,bonding and perpends atground level.

■ Plan number and projection ofcorbels.

■ Enquire whether purpose-madesolid or bed-faced bricks havebeen ordered for the corbelbricks.

■ Keep all projections equal.

■ Keep all corbel courses parallel.■ Level or line-up bottom arris of

corbel courses.■ Maintain backweight or ‘tailing

down’ as you go.■ Form full solid cross joints to

assist stability and strength ofcorbelling.

■ Carefully joint up underside ofcorbel courses.

5.9 TUMBLING-IN COURSES

Tumbling-in is a method ofreducing the plan section areaof brickwork between twolevels by providing a slopingweathered surface in place ofthe horizontal surface or ledgewhich would otherwise result.Tumbling-in was commonly

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CHOICE OF BRICKSThe faces of the bricks form thesloping weathered surface and itis usual to project the first courseof tumbling because it isimpractical to cut bricks to asharp edge along the exposedangle and difficult to finish themortar joint satisfactorily(fig 5.94).

The bricks and mortar in theweathered surface should bespecified as for a capping.Because the projection is notthroated, the bricks and mortarbelow the weathered surface

should be specified as for wallswith a capping (see Section 6.2‘Frost attack and frost resistance’,table 6.5 of Section 6.4‘Durability of brickwork’ forrecommended brick and mortardesignations and Section 5.1‘Copings and cappings’ fordefinitions and comments oncappings and copings).

TWO METHODS OF BUILDING

1. For small reductionsTumbling-in is set-out full size ona board to determine the sizeand shapes of cut bricks. Atimber template is made andused to maintain the requiredslope (fig 5.95).

2. For large reductionsTumbling-in courses are builtusing lines set to the requiredangle. Regularity of gauge isvery important (i.e. 4 courses to300 mm) and is maintained byusing a standard gauge rod tocheck each course of tumbling-inas these are set in position.

In both methods a bricklayer’slevel should be used inconjunction with a try square toobtain true, horizontal beddingcuts to the bricks (fig 5.96).

Clay engineering andperforated bricks are best cutwith a bench-mounted masonrysaw for neatness, accuracy andreduced wastage. Frogged

Figure 5.92. Tumbling-in to reduce anexternal chimney breast to a chimney.

Figure 5.93. Tumbling-in to reduce anattached pier.

Clay brickscategory (F)

25 mm

Figure 5.94. First course is commonlyprojected.

12 mm thickplywoodtemplate

Gaugemarkedoff

Gaugemarkedoff

25 mm

25 mm

Timbertemplate

Figure 5.95. ‘Gun’ templates tomaintain slope of short lengths oftumbling-in.

Figure 5.96. Bevel is set once to cut allbricks used in tumbling-in.

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TUMBLING-IN COURSES 153

bricks should be cut to avoida ‘vulnerable’ end by formingthe long side on the solid bedrather than on the froggedbed (see Section 2.5 ‘Cuttingbricks’).

ILLUSTRATED EXAMPLES

1. For small reductionsHalf-brick deep bonding pocketformed to receive tumbling-incourses (fig 5.97).

A gauge rod is used tocompare a whole number ofcourses of tumbling-in with awhole number of verticalcourses. In this case 8 and 7courses respectively give aslope of approximately 60degrees on a pier which projects11⁄2 bricks (337 mm) (figs 5.98& 5.99).

Every time the ‘gun’ template isused press the stem firmlyagainst the plumb face of theattached pier checking(a) Slope of face(b) That tumbling-in courses are

at right angles to template,using a try square.

2. For large reductionsBricklaying line fixed each side ofa longer length of tumbling-inwhere a template would beinappropriate (fig 5.100).

Gauge rod

Spacer block

Figure 5.97. Half-brick deep bonding pocket.

Figure 5.98. Use of ‘gun’ template. Figure 5.99. Completed pier.

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Optional thin plywoodtemporarily fixed eachside to keep tumbling-in vertical


Other examples• Methods of using tumbling-in

courses to finish a slopingfreestanding wall or thebalustrade wall to an externalstaircase are shown infigs 5.101 & 5.102.

• The solutions shown infigs 5.101 & 5.102 mightbe adapted to finish a gableparapet wall.

• Method of tying in abrick-on-edge capping tocheck the tendency to slidedownwards on the bed(fig 5.102).

• Reducing a chimney breaston an elevation to the size ofthe external chimney stack(fig 5.103).

Figure 5.100. Bricklaying lines replacing template.

Figure 5.101. Tumbling-in to a slopingfreestanding wall.

Figure 5.102. Tying in a brick-on-edgecapping.

Ultimate positionof stack

Line and pinsto maintaincorrect angle

50 × 25 mm battenFigure 5.103. Reducing a chimney breast.

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FIREPLACE OPENINGS, CHIMNEY BREASTS AND FLUES 155

In modern houses heating isprovided by central heatinginstallations and consequentlymany do not have a fireplaceor a chimney. However, anopen fire is widely regardedas an attractive feature andfireplaces are now often beingbuilt in modern houses asluxury features. They are oftenembellished with decorativedetail and so present arewarding opportunity todemonstrate a bricklayer’s skilland competence (figs 5.104& 5.105).

Regardless of the detail,design and visual attractionof a fireplace it will need tofunction effectively. To ensurethis the bricklayer mustappreciate the technicalrequirements of fireplace,chimney and flue installationsand the Building Regulationsthat apply to them. Theconstruction should becompleted in accordancewith the requirements andRegulations as well asdemonstrating neatnessand skill.

The design and constructionof fireplace openings,chimney breasts and flues arecontrolled by Part L of theBuilding Regulations. Furtheradvice and guidance can befound in BS 6461:‘Installationof chimneys and flues fordomestic appliances burningsolid fuel’ and in Part 1 ofthese regulations:‘Code ofpractice for masonry chimneysand flue pipes’.

These notes relate to theinstallation in domesticbuildings of fireplaces, fluesand chimneys for heatingappliances up to 45 kW output.

TYPES AND POSITION OFFIREPLACE OPENINGS

The Building Regulations thatdeal with fireplaces, chimneysand flues are mainly concernedwith the avoidance of the spreadof fire to the surroundingstructure and with the safedischarge of the products ofcombustion to the atmosphere.

In order to comply with theseRegulations open fires have tobe contained within a fireplacerecess. Careful considerationmust be given to its positionand construction.

Types of fireplace1. Chimney breast built to an

external cavity wall(a) Chimney breast

positioned within theroom (fig 5.106).

(b) Chimney breast builtexternally (fig 5.107).

This type has the advantageof not reducing the floor areaof the room.

2. Fireplace openings placedon internal walls(a) Single fireplace

(fig 5.108).(b) Back-to-back fireplace

openings (fig 5.109).This arrangement is quiteoften used in semi-detachedand terraced housing sothat flues can be collectedtogether to form onechimney stack.

5.10 FIREPLACE OPENINGS, CHIMNEY BREASTS AND FLUES

Figure 5.104. Decorative freestanding,double-sided fireplace.

Figure 5.105. Modern fireplace withfirewood compartment alongside.

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3. Other typesOther designs may involvecorner sited openings,freestanding and ‘through’(double-sided) fireplacearrangements (fig 5.110).

SIZES OF FIREPLACE OPENINGIn order to accommodate aparticular heating appliance,the fireplace opening should bebuilt to specified dimensions.The width, height and depth ofthe opening will depend on theparticular appliance or fireplaceaccessories to be accommodated,but to comply with Regulationsthe opening must be at least338 mm (11⁄2 bricks) deep andthe jambs must to be at least200 mm (1 brick) wide.

As the fireplace and flue areconsidered to form a structural

338

min

.

200minimum

Figure 5.106. Chimney breast positionedinternally in an external wall.

338

min

.

Figure 5.107. Chimney breast positioned externally in an external wall.

200 minimum

200 minimum

338

min

.

Figure 5.108. Fireplaceopenings placed oninternal walls.

200minimum

200minimum

338

min

.

Figure 5.109. Back-to-back fireplace openings.

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part of the building all walls mustbe taken down to foundation leveland a horizontal DPC provided toresist moisture rising up into thesuperstructure. The DPC will needto link with DPCs and/or DPMsadjacent to the fireplace opening.

Figures 5.111a & b illustratea typical design and minimumdimensions.

THE CONSTRUCTIONALHEARTH

To contain a fire safelyevery fireplace must have aconstructional hearth at its base.This is a concrete slab 125 mm

thick (minimum) that must extendinto the full depth of the openingand project in front of the faceline of the chimney jambs aminimum of 500 mm. It must alsoextend a minimum of 150 mm oneither side of the opening.

BRIDGING THE FIREPLACEOPENING

The fireplace opening must beclosed over at the top and thebrickwork over it must besupported. Flue liners in thechimney above also requiresupport. A British Standardsplayed reinforced concrete

DEFINITIONS

The following definitions are particular to fireplaces, chimneys and flues and are in addition to those for more generalterms listed in the Glossary of Terms included in this book (p. xi). They are taken from BS 6461.

Chimney a structure (including any part of the structure of a building) enclosing or forming part of a flue or fluesother than a flue pipe, including any opening therein for the accommodation of an appliance, but excluding theflue terminal

Chimney breast a projection beyond the thickness of a wall containing the fireplace and flue(s)Chimney connector an accessory that connects an appliance or flue pipe to a chimneyChimney jamb the walling at the side of a fireplace recessChimney stack part of a chimney enclosing one or more flues that rises above the roof of a building of which it forms

a part and which includes the chimney terminal, but not the flue terminalChimney terminal the uppermost part of a chimney stackFireplace recess a space formed in a wall or chimney breast into which an appliance may be placed and from which

a flue leadsFlaunching the weathering formed in mortar at the top of a chimney or base of a flue terminalFlue a passage that conveys the products of combustion from an appliance to the open airFlue block a factory-made masonry unit that can be erected on site to form a chimney. It may contain voids for either

insulation or for combustion airFlue lining a lining forming the wall of a flue for the purpose of protecting the chimney fabricFlue pipe a pipe used for connecting the appliance flue outlet to the chimney flue or to the outside atmosphere, but

not including a pipe used as a lining to a chimneyFlue terminal (chimney pot) a prefabricated or built-up unit forming the outlet end of a flueGather (oncome) the contraction over a fireplace recess to reduce it to the size of the flueLintel a load-bearing and/or throat-forming beam above the fireplace recessOffset a double bend introduced into a flue so that its direction remains parallel to its original direction. The effect is

to give the path of the flue a lateral displacementOversailing courses of stone or brickwork (masonry) arranged to project from the face of a wall or chimney stack

largely for decorative effectThroat that part of the flue, if contracted, which is located between the fireplace and the chimney flueWithe (midfeather, bridge, brig) a partition between adjacent flues in a chimney

Figure 5.110. Circular freestandingfireplace with raised hearth.

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lintel is specifically designed andmanufactured for this purpose(fig 5.112).

In addition to providingsupport for the brickwork andflue liners over the opening, thesplay at its back forms arestricted throat for the flue waywhen used in conjunction with afireback – a prefabricated unit offireproof material that lines the

back and sides of the fireplace.This restriction improves the flowof flue gases from the fireplaceand up into the chimney. Thelintel is formed with ‘wall holds’(squared ends) to assist beddingit in the jambs.

In conjunction with the splayedlintel the brickwork on each sideof the opening behind it, has tobe ‘gathered over’ to form aseating for the flue liners above;this has to be built by thebricklayer by forming a numberof splayed corbels (‘oncomes’) oneither side until the opening isreduced to a width to suit theflue liner (fig 5.113).

PRE-CAST THROATING UNITPrefabricated pre-cast concretethroating units are available as analternative to the splayed lintel,fireback and corbelling describedabove. They are manufactured tosuit standard plan dimensionsand have three functions:

(i) bridging the fireplace openingand providing support forbrickwork above

a.

Minimum 150 on eitherside of fireplace opening

Constructional hearth 125 mm thick

Constructional hearth minimum 125 mm thick

b.

Flue liner

B.S. splayed reinforcedconcrete lintel

DPC atspecified level

Minimum500

Figure 5.111. a: Plan and b: Section of typical fireplace design showing minimumdimensions required by regulations.

Figure 5.112. Isometric rear view ofB.S. splayed reinforced concrete lintel.

Splayed corbels tiedinto chimney breast

Figure 5.113. Arrangement of splayedcorbels from chimney breast to ‘gather’opening into flue.

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(ii) forming part of the restrictedthroat requirement

(iii) gathering the fireplaceopening to provide astructural seating for thefirst flue liner. Alternativefittings provide forcircular or square liners(fig 5.114).

FLUE LINERSBefore the 1960s chimneys werevery rarely lined, instead theywere internally rendered with

lime mortar parging, orpargeting. With the advent ofmodern solid fuels chimneysbecame more vulnerable todamage by the products ofcombustion, as solid fuelscontain greater concentrationsof carbon dioxide and sulfur.As flue gasses reached thecolder air at the top of thechimney stack, condensationof water vapour would occur.The condensate, running backdown the flue, dissolved carbondioxide and sulfur to form a

mixture of weak carbonic andsulfuric acids. Over a number ofyears this acid would seep intoand attack the lime mortar ofthe parging and the joints of thebrickwork, causing it todisintegrate and fall downthe flue.

To avoid this problem theBuilding Regulations madethe installation of flue linerscompulsory (figs 5.115 & 5.116).

Purpose-made flue liners aremanufactured from clay orrefractory concrete, both ofwhich are non-combustibleand are resistant to damageby flue gas condensate.

Liners are manufactured invarious sizes and are eithercircular or square in section.They have rebated or socketedjoints to provide an effective sealand it is very important that thebricklayer installs them thecorrect way up otherwise flue gascondensate can seep through thejoints and cause damage in thebrickwork beyond. Liners mustalways be fixed with sockets orrebates facing up to receive theplain or spigoted end of thenext liner.

When starting to build a flue,first check that every flue liner issound and fit for its purpose.They should all be free fromcracks and splits, and the endsshould not be damaged.

In all cases the flue linersshould be positioned ahead ofthe brickwork being built aroundthem. Proper joints should bemade between the liners,usually in the same mortar asthe rest of the chimneyconstruction. All joints betweenthe liners should be full andfinished to leave a clean internalbore inside the flue.Figure 5.114. Proprietory pre-cast throating unit.

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The space between theoutside of the flue and thesurrounding brickwork shouldbe filled with a suitablematerial that willallow expansion to take place,

with no resultant damage.Suitable materials are:

1. A weak lime/sand mortar2. Insulating concrete (usually

a mix of exfoliatedvermiculite granules witha small amount of ordinaryPortland cement).

THE DESIGN ANDCONSTRUCTION OF FLUES

The design of houses up to50 or 60 years ago encouragedthe use of fireplaces in everyroom of the building. Flues builtin brickwork would travel invarious directions in order thatthey might be collectedtogether to form a chimneystack. In modern construction itis common for only onefireplace, if any, to beconstructed within a dwellingand therefore only one flue isrequired.

Flue travelIn many cases nowadays,architects will specify that thevertical line of the flue shouldbe offset by at least thedimension of its width, althoughthere are no proven benefits fordoing this.

This offsetting of the flue istermed ‘flue travel’ and isrequired when the collection offlues to form one chimney stackis necessary.

To achieve the desiredtravel, purpose-made linerbends are used. The flue can bemoved in any direction, but theangle of the flue should be nomore than 30° from the vertical(fig 5.116).

The design and detail offireplace openings, chimneybreasts and flues may differconsiderably according tolocation and the heatingappliance to be accommodated.However, the bricklayer should

Weak lime mortar orinsulating concrete

Plan view of chimney stack

Section through lined flue

Figure 5.115. Modern flues are linedwith clay or refractory concrete flue liners(plan and section).

Figure 5.116. Flue liners are manufactured straight and curved.

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CHIMNEY STACKS FOR DOMESTIC FIREPLACES 161

appreciate and understandthe basic principles involvedin their construction as theyapply to all designs and needto be properly implemented forthe successful functioning ofthe installation.

References• BS 1251:1987 ‘Specification for

open-fireplace components’.• BS 6461:1984 ‘Installation

of chimneys and flues fordomestic appliances burningsolid fuel’.

• Part 1:1984 ‘Code of practicefor masonry chimneys and fluepipes’.

• BS 1180:1999 ‘Specification for clayflue terminals’ and BS EN1457:1999 ‘Chimneys andclay/ceramic flue liners.Requirements and test methods’.

Emphasis is placed on theneed for damp-proof coursetrays and flashings to preventrainwater penetration wherethe stack penetrates the roofand it is essential that thebricklayer has a good workingknowledge and understandingof the correct installation ofthese.

POSITION OF CHIMNEYOUTLETS

The position and height of achimney outlet can play a majorpart in the efficiency of afireplace and flue.

It is very important that thechimney terminates in a positionwhere the products ofcombustion do not become

either a health hazard or a firerisk. Building Regulations requirethat flue gases should bedischarged out of the buildingclear of any window, rooflight orother openings and sufficientlyfar from any material whichmight ignite if it was to be incontact with hot flue gases orsparks.

Wind and the effects ofadjacent structures, trees, etc.,cause zones of high and lowpressure about buildings. A lowpressure zone would generallyoccur on the lee side of theridge of a pitched roof, andclose to the windward side of aflat roof (10° or less isconsidered to be flat).Corresponding zones of highpressure are developed on the

KEY POINTS

■ Check that all special fireplacecomponents to be built in are tohand, are the required size andare undamaged.

■ Check that a sufficientnumber of the flue liners areto hand and that they areundamaged.

■ Check the proposed level forDPC with regard to continuitywith adjacent DPCs and DPMsin floor construction.

■ Locate and set-outthe constructional-hearthaccurately.

■ Locate and set-out fireplaceopening and chimney breastsaccurately.

■ Continually check line, level,plumb and gauge.

■ Take particular care to fix theflue liners the correct way up(socket facing up).

■ If the fireplace and chimney areto form a decorative brickworkfeature check the Key Pointslisted in Section 5.6 ‘Decorativebrickwork’. Also those in 5.3‘Curved arches’ and 5.5 ‘Soldierarches’ as appropriate.

■ Select bricks for exposed internalface work with particular care aswork of this nature is likely toget close and frequent scrutiny.

■ Keep work clean and protectpartially completed work duringbreaks.

■ Protect the whole feature oncompletion while awaitinghandover.

5.11 CHIMNEY STACKS FOR DOMESTIC FIREPLACES

The construction of chimneystacks and flues is quite acomplex task, calling for theintegration of work bycraftspeople dealing withcarpentry, roofing, plumbingand bricklaying. The bricklayerneeds to grasp the overallrequirements of this work andensure that they are appliedcorrectly.

This section complementsthe previous one about theconstruction of fireplaces andflues. It deals with the siting ofa chimney stack and itsconstruction as it passesthrough the roof surface andinto the open air above. It alsocovers detail of the design andconstruction of the chimneyterminal.

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opposite sides of the roof. Theposition and design of achimney outlet should beconsidered in relation to thesepressure zones as they mayseriously affect the efficiency ofthe flue.

Theoretically a flue is likely tofunction well if the outlet is inthe low pressure zone as the fluegases would be drawn out intothe atmosphere. Flue gaseswould be driven back into thebuilding if the outlet was in ahigh pressure zone. Because thedirection of the wind varies atdifferent times, pressures abouta roof surface change andtherefore chimney outletsshould be sited sufficiently abovea roof surface to avoid thesepressure effects.

To satisfy normal requirementsfor the effective and safeworking of flues their outletsshould not be sited withinthe shaded areas shown infigs 5.119a & b.

HEIGHT AND STABILITY OFCHIMNEY STACKS

To ensure the stability of chimneystacks, the Building Regulationsrequire that the height of anunrestrained chimney should notbe more than 4.5 times its leastwidth at the level it penetratesthe roof surface (fig 5.120).

This limitation is likely torestrict the use of a chimney ofminimal dimensions (440 mm – 2bricks) in steeply pitched roofsunless they are located at or nearthe roof ridge. For example, thediagrams indicating the requiredheights of flue outlets show thata chimney terminal must beabove any part of a roof surfacewithin a horizontal distance of2.3 m; therefore a brickworkchimney located at the eaves ofa 45° pitched roof would have tobe a minimum of 2.3 m high andtherefore its minimum widthwould be 565 mm (21⁄2 bricks).

For tall stacks special structuraldesign might be necessary,

perhaps incorporating horizontalbracing to improve stability.

CONSTRUCTION OF CHIMNEYSTACKS

All chimney stacks, whether asa single flue or a number offlues grouped together, shouldbe constructed in such a waythat every flue is surrounded byat least 100 mm of solidmasonry. Each flue must serveonly one fireplace or heatingappliance.

A chimney stack is one of themost exposed parts of anybuilding and thereforeappropriately durable materialsshould be selected and thehighest standard of workmanshipmaintained throughout itsconstruction.

THE TOP OF A CHIMNEY STACKDue to its exposed position at thetop of the stack the flue terminal,

a.

b. Figure 5.118. Chimneys are also afeature in recent domestic architecture.

Figure 5.117. Historically chimneys haveoften been major decorative brickworkfeatures especially in Tudor architecture.a: Hampton Court Palace, b: Rye House,Essex.

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or chimney pot, should bebedded into at least 3–4 coursesof brickwork. This will ensurethat it is well anchored and notlikely to be dislodged by strongwinds.

The top of the stack mayincorporate oversailing courseswhich are frequently moredecorative in nature thanfunctional. The top surface ofthe chimney surrounding the flueterminal, or chimney pot, mayconsist of a sand and cementweathering, or flaunching, todrain away rainwater rapidly inwet weather. Alternatively, andproviding more effectiveprotection than flaunching,an impervious, weathered,overhanging and throated copingmay be installed. If the coping isjointed, it should be set on a DPCsandwiched in mortar. This willshed rainwater quickly, throwingit clear of the stack below.

WATER PENETRATION ANDCHIMNEY STACKS

The detail design andconstruction of a chimney stackshould be considered in relationto the prevention of penetrationby rainwater:

1. passing through the jointbetween the roof surface andthe masonry of the chimneystack

2. entering the masonry aboveroof level and percolatingdown within it, bypassing theflashings at the roof/chimneyjunction

3. penetrating the masonry ofthe stack to the surface of theflue liner and from thererunning down to lower levelswithin the building.

a.

b.

600

600*

*1 m in Northern Ireland

At least 1 m inNorthern Ireland

2300 1000

1000

1000Adjacent oradjoiningbuildings

1000

Rooflight

2300

Openablefanlight

2300 2300

Maximum – 4.5 x leastbase dimension of stack

Section

450

mm

Plan

Figure 5.119. Flue outlet should terminate outside of the shaded areas. (a) Roof witha pitch of 10° or greater. (b) Roof with a pitch of less than 10°.

Figure 5.120. Maximum height of an unbraced chimney stack.

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Lead DPC trays and flashingsare required and these areusually formed by a plumber.Trays and DPCs are installed bythe bricklayer but generallythe plumber fits the flashings.However, the bricklayer needs tohave a good working knowledgeof the total assembly and howan effective construction is built.Good design points are illustratedin fig 5.124 and include:

1. Chimney abutment flashingscomprising stepped andlapped raking flashings, a backgutter and flashing and anapron flashing. These providea barrier to water entering thejoint between the roof surfaceand the chimney stack.

2. A pre-formed DPC tray withupstands at the back and twoside edges and a projection atthe front to dress down overthe abutment flashing to befitted below. The tray shouldbe taken through a jointbetween the flue liners anddressed up on the inside of theliners a minimum distance of25 mm. This tray is to preventwater that may penetrate themasonry above the roof frommoving down within it andinto the building. It is built intothe stack where the chimneyintersects with the roof planeat its lowest point.

3. In steeply pitched roofs, andparticularly where severeexposure to wind-driven rainis anticipated, an additional,but simpler, DPC tray isinstalled at the higher levelchimney/roof planeintersection. This is intendedto reduce the amount ofwater that may reach thelower tray. Opinions vary

Figure 5.121. A variety of clayware flue terminals.

Figure 5.122. Chimney terminated withdentils, oversailing courses and flaunchingaround chimney pots.

Figure 5.123. Chimney terminated withpre-cast coping, weathered and throated togive good weather protection.

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about the correct positioningof DPCs and trays in chimneystacks and some architectsand/or local authorities mayprefer a variation of the aboverecommendations.

To prevent a risk of itscorrosion when in contact withmortar, lead built into a chimneystack as a tray should be coatedwith a solvent-based bituminouspaint on both sides before

installation. Flashings do notneed a bituminous coating asthey are not built into the mortarjoints of the brickwork by morethan 25 mm and therefore arenot vulnerable to corrosion.

Terminal

Flaunching

Capping

Damp-proofcourse

Chimney stack

Cover flashing

Back gutterflashing

Tilted filletfixed to gutterboard

Angle blockfixed totrimmer tosupportgutter board

Trimmer

Pot or projecting liner

Coping

Damp-proofcourse

55 mm

Section through chimney stack and terminalshowing alternative constructions

Flue liner

Damp-proof course tray

Damp-proof course tray

Front apron flashing

Trimmer

Rafter

Section through brickwork chimney

Figure 5.124. Section through chimney showing good design features.

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a.

b.

c.

CONSTRUCTIONStage one: Raise the brickworkup to two courses above thelower point of intersection withfinished roof and bed thespecially-shaped DPC tray withupstand edges (fig 5.125a).

To enable the tray to continueinto the flue, and be dressed upon the inside of the liners aminimum distance of 25 mm,a joint in the flue liner mustcoincide with the position ofthe DPC tray. This joint should bea butt joint (not a socket) andmay require a specially cut linerto suit.

Figure 5.125. Construction sequence of chimney/roofintersection. a: stage one, b: stage two, c: stage four.

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Stage two: Continue buildingthe stack, leaving the mortar jointssuitably raked out in readiness toreceive lead flashings (fig 5.125b).

If there is uncertainty aboutthe exact position of the joints tobe raked out, it is better to rakeout too many joints than to haveto cut out hardened mortar later;they can be pointed if notrequired. If a plumber is availableseek advice.

Stage three: Bring brickworkup to two courses above theback gutter level and lay thesecond DPC tray.

Stage four: Continue buildingthe stack to the required height(fig 5.125c).

Stage five: Form anyoversailing courses and completethe terminal as specified.

References• BS 6461-1:1984 ‘Code of practice for

masonry chimneys and flue pipes’.• ‘Rolled Lead Sheet – The Complete

Manual’ 2003. The Lead SheetAssociation.

Figure 5.126. Chimney completedawaiting flashings to roof.

Figure 5.127. Not all chimneys aresquare.

KEY POINTS

■ Check types of bricks and mortarare as specified orrecommended.

■ Check mortar mixes are asspecified or recommended.

■ Check that proposed heightand location of chimneyterminal conform to regulationswith reference to distanceabove roof surface and any roofopenings.

■ Check that the minimum widthof the stack is adequate for theproposed height.

■ Check that the pre-formed leadtrays have been correctly madeto size and configuration andthat there is a protective

bituminous coating on bothsides.

■ Check that flue liners are laid thecorrect way up, i.e. with socketsor rebates pointing up (seeSection 5.10 ‘Fireplace openings,chimney breasts and flues’).

■ Check that a flue liner jointcoincides with the position ofthe DPC tray. A specially cut linerto suit may be required.

■ Bed DPC trays and the DPC atthe terminal on fresh mortar.

■ Leave mortar joints recessed tosuit roof abutment flashings.

■ Check that coping and chimneypot, or flue terminal, areavailable for installation.

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6 BACKGROUND TOPICSThis section contains articlesrelating to technical aspects ofbrickwork performance. They areintended to help the readerunderstand the reasons why some

of the details of specification andconstruction exist and why it isimportant to comply with goodpractice guidance in the assemblyof the work.

Also included in this section arearticles on understandingdrawings, the care and use oftools and the manufacture ofbricks.

6.1 EFFLORESCENCE AND LIME STAINING

An understanding of thecauses of efflorescence andlime staining enablesbricklayers, brickworksupervisors and designers toplay an appropriate part inminimising the risk of theiroccurrence.

DEFINITIONSCommon efflorescence is adeposit of soluble salts left onthe surface of brickwork whenthe water in which they weredissolved evaporates (fig 6.1).(1)

Lime staining is a depositof lime left on the face ofbrickwork when the water inwhich it was dissolvedevaporates (fig 6.2).

Because these two undesirableoccurrences are superficiallysimilar but have different causesand manifestations and requiredifferent actions to prevent andtreat them, they are dealt withseparately.

EFFLORESCENCEThe most common form ofefflorescence is an unsightly butharmless white deposit whichdoes not affect the durability of

the brickwork and normallydisappears from new buildingswithin the first few months. Thevery rare forms of efflorescencewhich may cause physical harmare beyond the scope of thissection.

THE SOURCES OF SOLUBLESALTS

Common efflorescence derivesmainly from soluble salts that arecontained in clay bricks andsands used for mortars butsometimes in other sources.

Figure 6.1.Efflorescence.

Figure 6.2. Limestaining.

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EFFLORESCENCE AND LIME STAINING 169

ClaySalts in clay are most commonly,sulfates of sodium (Glauber’s salt),potassium (sulfate of potash),magnesium (Epsom salts) andcalcium (gypsum). Ferrous sulfateis not common in clays used forbrickmaking today but where itoccurs it may be responsible forrusty stains on mortar or bricks(fig 6.3).

Mortar sandsMost sands come from pits orriver beds and contain few salts.Sea sands contain many harmfulsalts and should not be used formortars unless they have beeneffectively washed by a reliablesupplier.

CementFortunately, in Britain, Portlandcement is most commonly usedand its contribution toefflorescence is minimal. Some ofthe slag cements used abroadcontain appreciable quantities ofsodium sulfate which is acommon cause of efflorescenceand this should be consideredbefore using such cements.

Detergents used as plasticisersMany detergents contain sodiumsulfates and should under nocircumstances be used in place ofproperly formulated proprietarymortar plasticisers (see Section4.1 ‘Mortars’).

Other sourcesBricks may absorb salts from ashesor the soil on which they arestanding or from materials stackedor heaped in contact with them.

How efflorescence formsWater dissolves soluble salts inthe bricks and mortar and holds

them in solution. As the waterevaporates and the wall dries outthe solution becomes moreconcentrated until salts begin tobe deposited. This may occur outof sight within the pores of thebrick or on the surface.

Exactly where, when and howmuch efflorescence will occur, isdifficult to predict beingdependent on complex chemicaland physical conditions such asthe type of salts, the rate of dryingby wind and sun and the degreeof saturation of the brickwork. Thelatter is the only condition whichwe can readily control.

Minimising the risk ofefflorescenceThe risk cannot be entirelyavoided as it is not practicable toeliminate all salts from bricks andmortars nor keep them virtuallydry, but it can be minimised byreducing the amount of waterpenetrating the brickwork.

Design detailsDesigners can use ‘umbrella’details which protect the

brickwork from saturation.Such details include effectiveroof verges and eaves, copingsand sills to shed run-off waterclear of the brickwork below(see Section 5.1 ‘Copings andcappings’). They should alsoavoid details which shed wateron projecting plinths and otherfeatures.

Site practiceBricklayers and site supervisorsare responsible for good sitepractice. Bricks should bestacked clear of the ground onpallets or by other means.Mortar materials should be keptfree from contamination, andbricks in stacks, on thescaffolding and newly builtbrickwork protected fromsaturation, particularly duringthe seven days after bricklaying(see Sections 1.2 ‘Protection ofnewly built brickwork’; 4.1‘Mortars’).

Scaffold boards adjacent tothe brickwork should beturned back during rain toavoid splashing causing a bandof efflorescence as well asmortar stains.

Damp conducted acrossmortar encrusted wall ties hasbeen observed to causeefflorescence on internalfacework.

Choice of bricksAlthough BS EN 771-1(2) makesprovisions for the manufactureto declare the content of activewater soluble salts in a brick itis important to realise that thedeclaration may have little, ifany, correlation with theliability of the brickwork toeffloresce.

Brickwork containssoluble salts

Brickworksaturated –dissolves salts

Brickwork driesout – solutionmigrates tosurface

Water evaporates–soluble saltscrystallise onsurface

1

2

3

4

Figure 6.3. Efflorescence – a simplifieddiagram.

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170 BACKGROUND TOPICS

Efflorescence can be avoided, orat least minimised, by appropriatedesign detail and good sitepractice as described above.

Treatment of efflorescenceIt is best to allow efflorescence toweather away naturally. Do notuse acid treatment, as apart fromthe danger to people andmaterials by inexpert use somesalts such as vanadium may befixed permanently. Light brushingwith a bristle, never a wire, brushmay be allowed.

Internal efflorescence may betreated by dissolving smallpatches with very little water,say a fine mist spray. The surfacemay then be dried with anabsorbent material but, as someusers have reported that thissometimes causes a blotchyappearance, it is advisable toexperiment on a smallinconspicuous surface at first.The absorbent material must beconstantly renewed or washedfree of salts.

LIME STAININGLime which stains the face ofbrickwork is often derived fromthe Portland cement in mortar oradjacent concrete as well.Although it might seem anobvious source, the hydratedlime in some mortars does notseem unduly to increase theliability of the brickwork to limestaining.

How lime staining formsWhen newly built brickworkbecomes saturated in its early lifeand as the Portland cement sets(hydrates) it releases lime intosolution. On drying out, calciumhydroxide is precipitated at the

surface (especially on mortarjoints) and converts to insolublecalcium carbonate by reactionwith carbon dioxide from theatmosphere. Lime staining may,of course, be accompanied byefflorescence salts (fig 6.4).

Minimising the risk of limestainingIt is absolutely essential toprotect newly built ‘green’brickwork from saturation duringthe first 24 hours and very

important to maintain thatprotection for at least 7 days(see Section 1.2 ‘Protection ofnewly built brickwork’).

Brickwork should be separatedby a damp-proof membrane fromcontact with concrete that maybecome wet, in order to preventthe transfer of lime and salts insolution from the Portlandcement in the concrete throughthe brickwork to the face or bywashing directly over it. As thereis much more Portland cement inconcrete than in mortar thestaining from concrete can beparticularly heavy.

Treatment of lime stainingUnlike common efflorescence,lime staining is insoluble and canbe removed only by expert andexpensive treatment.

References(1) Definition of efflorescence derived

from ‘Brickwork: Efflorescence.A perennial problem re-examined’Structural Clay Products Ltd. 1974,(out of print) by B. Butterworth,B.Sc., ARICS, F.I.Ceram., formerlyon the scientific staff of theBuilding Research Station.

(2) BS EN 771-1:2003.

Unprotected newlybuilt ‘green’brickwork becomessaturated

Portland cement setsand releases limeinto solution

Brickwork dries out –calcium hydroxideprecipitated onsurface

Calcium hydroxideconverts to insolublecalcium carbonate

1

2

3

4

Figure 6.4. Lime staining – a simplifieddiagram.

KEY POINTS

■ Do not stack bricks on soil orashes.

■ Protect stocks of bricks, sandsand mortars from contaminationand saturation.

■ Do not use sea sands formortar unless effectivelywashed.

■ Slag cements may contributeappreciably to efflorescence.

■ Use only proprietary mortarplasticisers, never detergents.

■ Protect ‘green’ brickwork fromsaturation to prevent limestaining.

■ Continue to protect the top ofincomplete brickwork tominimise efflorescence.

■ Separate brickwork frompotentially wet concrete with aDPM.

■ Efflorescence may derive fromsoluble salts in the brick, mortarmaterials or outside sources.

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FROST ATTACK AND FROST RESISTANCE 171

Brickwork is at risk from frostdamage as the temperaturefalls below freezing only if it issaturated at the time.

The risk can be minimised bydesigning and building to avoidsaturation or by using frostresistant bricks and mortar.

FROST ATTACK – THE CAUSES• When materials are saturated

their pore structures arevirtually filled with water.

• When water freezes itattempts to expand. Ifenclosing materials are unableto resist the stresses they willbe disrupted, an action knownas frost attack leading to frostdamage.

• Materials liable to frostdamage will be at greater riskthe closer they become tobeing saturated and the moreoften the temperature fallsbelow freezing while they aresaturated. Freezingtemperatures alone do notresult in frost attack.

• Bricks which suffer frostattack may crumble or theface may spall away.

• Mortars which suffer frostattack will lose strength,adhesion to the bricks and beliable to erosion.

FROST RESISTANCE OF BRICKSThe resistance of bricks andmortars to frost attack, theimportance of workmanshipand the way design can limitsaturation are described below.

Fired-clay bricksManufacturers are required byBS EN 771-1(1) to declare thefreeze–thaw resistance of theirbricks in one of the followingcategories.

Frost resistant: F2 SevereexposureDurable even when saturatedand subjected to repeatedfreezing and thawing.

Moderately frost resistant: F1Moderate exposureDurable except when saturatedand subjected to repeatedfreezing and thawing (fig 6.5).

Not frost resistant: F0 PassiveexposureLiable to be damaged byfreezing and thawing andnot normally for useexternally. The freeze–thawtest has been included in

the European Standard formasonry products. There is noother way of predicting thefrost resistance of clay bricks.In particular there is nodirect relationship betweeneither compressive strength orwater absorption and frostresistance.

Calcium silicate (sandlime andflintlime) bricksCalcium silicate brickmanufacturers are not required,to classify their bricks for frostresistance and generally there islittle risk of them being damagedby frost. There is a relationshipbetween the compressivestrength and frost resistance ofcalcium silicate bricks andrecommendations are made forthe use of bricks not less thancompressive strength class 4(27.5 N/mm2) in very exposedconditions.

6.2 FROST ATTACK AND FROST RESISTANCE

Figure 6.5. Frostattack on moderatelyfrost resistant bricks ina capping.

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Mortars – vulnerability at anearly ageMortars are particularlyvulnerable before they have set,as once frozen they will not setsubsequently. They will bepermanently damaged andnormally the brickwork will haveto be taken down and rebuilt.

Bricklaying should be stoppedwhen a falling air temperaturereaches 3°C. Once freezing hasoccurred bricklaying should notbegin again until the temperaturereaches 1°C and is rising, andthen providing only that thebricks are not frozen.

Newly built brickwork must beprotected from freezing beforethe mortar has set (see Section1.2 ‘Protection of newly builtbrickwork’).

‘Antifreeze’ admixturesThere are no known ‘antifreeze’admixtures that are successful inbricklaying mortars and some arepositively harmful. This is referredto in section 4.1 ‘Mortars’ andmore fully in section 3.1‘Avoiding damage from extremesof temperature’.

Mortars – long term frostresistance• Whichever type of mortar is

used, cement:lime:sand,cement:sand and plasticiser,or masonry cement:sand, itsfrost resistance will beenhanced as the proportion ofcement is increased.(see Section 4.1 ‘Mortars’,particularly table 4.1)

• Where there is a low risk ofsaturation a designation M4mortar will give a goodbalance of properties forexternal walling in the UK.In conditions of extreme

exposure, either resultingfrom geographic position orof particular brickworkfeatures, to wind-driven rainand freezing temperatures,designation M6 or evendesignation M12 mortars maybe advisable partly to provideresistance to sulfate attack(see Section 6.3).

• Designers are responsible forspecifying appropriate mortardesignations and sitesupervisors and operatives foraccurate batching and correctmixing as described in thesection on mortars.

• When pointing brickwork,ensure that the mortar is

compacted so that no airpockets remain to fill withwater, freeze and dislodgethe pointing.

Brickwork features liable tosaturationBrickwork most liable tosaturation and freezing includes:

• Horizontal and slopingsurfaces, e.g. copings andcappings, sills, projectingcourses and plinths.

• Vertical surfaces subject torun-off water from cappings,sills without projections andeffective throats, and fromareas of glazing and

Figure 6.8. Frostattack on moderatelyfrost resistant bricksnot protected fromsaturation by waterfrom retained earth.

Figure 6.6. Frost attack on inadequatedesignation mortar saturated by waterrun-off on sloping plinth.

Figure 6.7. Frost attack on moderatelyfrost resistant bricks saturated by run-offfrom hard paving.

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SULFATE ATTACK ON MORTARS 173

impervious wall cladding andsplashing of rain-water fromadjacent hard paving.

• External walls below or within150 mm above ground levelin poorly drained soil.

• Any brickwork in severelyexposed areas which may besaturated by driving rain andliable to freezing.

GUIDANCE ON THE CHOICE OFBRICKS AND MORTARS FOR

SPECIFIC CONDITIONSIn practice, the selection ofsuitable bricks and mortars musttake into account sulfate attackas well as frost attack (seeSection 6.3).

Detailed recommendations forbrick and mortar designations aregiven in table 13 of BS 5628-3(2).Similar recommendationstogether with explanatory notesare given in a BDA publication ondurability.

The recommendations aresummarised in this book insection 6.4 ‘Durability ofbrickwork’(3).

In all situations particular caremust be taken to batch and mixmortars accurately and effectively.

References(1) BS EN 771-1: 2003.(2) BS 5628-3:2001 ‘Use of masonry’.

(3) ‘Brickwork durability’ BDA designnote 7. September 1986.

Figure 6.9.Moderately frostresistant bricks aresatisfactory whereprotected fromsaturation by roof eaves.

KEY POINTS

■ Brickwork is at risk from frostattack only when saturated.

■ The frost resistance of clay brickscannot be judged by either theircompressive strength or theirwater absorption.

■ Calcium silicate bricks aregenerally frost resistant andthere is a relationship betweenstrength and frost resistance.

■ Mortar is particularly vulnerablebefore it sets.

■ Frost resistance of mortars isenhanced with higher proportionsof cement.

■ Accurate batching and effectivemixing is essential.

■ ‘Antifreeze’ admixtures areineffective in brickwork mortars.

6.3 SULFATE ATTACK ON MORTARS

Sulfate attack on mortars isfortunately very rare and slowto develop, but can be costlyto remedy. It can be avoidedby a few simple safeguardswhich are mainly theresponsibility of designers and

specifiers supported byconscientious workmanship.This section provides anecessary understanding ofthe causes with somerecommendations for avoidingand minimising the risk.

THE PROCESS OF SULFATEATTACK

Sulfate attack on mortarsprincipally results from achemical reaction betweensulfate in solution and aconstituent of Portland cement,

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tricalcium aluminate (C3A)which forms calciumsulfoaluminate (ettringite)(fig 6.10).

The surface of the mortar jointmay crumble and erode (fig 6.11)and the inside expand, disruptingand even bowing the brickwork(fig 6.12).

The chemical reaction canoccur only if ample amounts ofwater continually percolatethrough the brickwork and themortar remains wet for longperiods. The slow movement ofwater by diffusion alone will notcarry enough sulfate to thecement.

Water may continuallypercolate through brickwork inmany ways, e.g.

• through copings, cappings orsills that have no effectiveDPC under them.

• by evaporation throughretaining walls in which theretaining faces have noeffective damp-proofmembranes.

• by running off imperviouscladding onto brickworkbelow or from paving intoadjacent brickwork.

• by exceptional exposure towind-driven rain.

SOURCES OF SULFATEA high proportion of clay brickscontain some soluble salts,including sulfates. Manufacturersare required by BS EN 771-1(1) todeclare the active soluble salts

Continual,heavypercolationof water

Sulfatedissolved

Sulfates andC3A react

Mortarcrumbles,expands andcracks

1

2

3

4

Figure 6.10. Sulfate attack – a simplifieddiagram.

Figure 6.11.

Figure 6.12. Parapetbows from maximumsulfate attack onmortar facing theprevailing wind-drivenrain.

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SULFATE ATTACK ON MORTARS 175

content for their bricks as either‘Normal’ S1 or ‘Low’ S2 category.

Soil, ground or sub-soil watersand made-up ground or fill maycontain sulfates which in verywet conditions can penetrate insolution to the cement.

Ashes and clinker, spread overground to be used for storingmaterials, can transfer sulfatesinto bricks stacked in contactwith them.

Calcium silicate bricks arevirtually free from sulfate and donot contribute to sulfate attack.

AVOIDING AND MINIMISINGTHE RISK OF SULFATE ATTACK

‘Sulfate attack of brickwork willtake place only under certainconditions: removal of any one ofthese conditions would preventsulfate attack and probablyaccounts for the relatively fewinstances of deterioration’(2).

Some of the conditions andways to eliminate them arereferred to here.

Protecting brickwork fromsaturationWhere a choice exists, the surestway to prevent sulfate attackis to protect the brickworkfrom being saturated for longperiods. This protection can beachieved by careful design andconstruction that will preventcontinual water percolationthrough the brickwork.

Appropriate and effectiveprojecting and throated copings,sills, verges and eaves, normallyprotect brickwork fromsaturation, except possibly inareas of exceptionally severewind-driven rain.

Brickwork earth-retaining wallsshould have the retaining faceprotected by an effective

membrane that has afree-draining material behind.

Provisions where brickwork maybecome saturatedCement rich mortarsSulfate attack can occur only ifsulfate solutions penetrate themortar. Cement-rich mortars,e.g. designations M12 and M6are more resistant to waterpenetration and hence to sulfatedespite their higher proportion ofC3A (see Section 4.1 ‘Mortars’ orSection 6.4 ‘Durability ofbrickwork’ for the table of mortardesignations).

To minimise the risk ofbrickwork cracking, manufacturersof calcium silicate bricks generallyrecommend using mortars nostronger than designation M4.This is normally satisfactory asthe bricks are virtually free ofsoluble salts.

Clay bricks with a level of solublesalt (S2)Sulfate attack in brickwork builtfrom S2 category bricks anddesignation M12 or M6 mortars isvirtually unknown, suggesting thatthis combination practicallyeliminates the risk of sulfate attack.

Sulfate-resisting cementIf brickwork is to be built fromclay bricks, of ‘normal’ S1 solublesalts content and it is likely to

remain saturated for long periods,sulfate-resisting cement should beconsidered in certain conditions.Its use should also be consideredwhere sulfate ground conditionsexist.

GUIDANCE ON THE CHOICE OFBRICKS AND MORTARS FOR

SPECIFIC CONDITIONSIn practice the selection ofsuitable bricks and mortarsmust take into account frostresistance as well as sulfateattack (see Section 6.2).

Detailed recommendations forbrick and mortar designations aregiven in table 13 of BS 5628-3(3).

The recommendations aresummarised in this book insection 6.4 ‘Durability ofbrickwork’.

References(1) BS EN 771-1:2003.(2) Harrison W. H., ‘Conditions for

sulfate attack on brickwork,chemistry and industry’ 19September 1981.

(3) BS 5628-3:2001 ‘Use of masonry’(see note below).

NOTE: For those not having accessto BS 5628-3, the BDA publication‘Brickwork durability’ as revised onSeptember 1986 contains tablesbased on the information in table 13of the code with useful explanatorynotes.

KEY POINTS

■ Sulfate attack on mortars is rarebut usually costly to remedy.

■ It can occur only by persistentwater percolation throughbrickwork.

■ Persistent percolation canusually be avoided byappropriate design.

■ Experience suggests that inconditions of severe exposure tosaturation, if ‘low’ S2 categorybricks are used with cement-richmortars, sulfate attack is unlikely.

■ Sulfate-resisting cement shouldbe considered in certainconditions.

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The two preceding sections,6.2 and 6.3, deal with the maincauses of the deterioration ofbrickwork. The more commonis frost attack on bricks andmortars. Sulfate attack onmortars is far less common.

Frost and sulfate attack occuronly if brickwork becomessaturated. The degree ofsaturation depends:

• on design details, e.g.projecting and throated sillsgive better protection thanflush sills.

• on workmanship, e.g. badlyinstalled DPCs under copings.

• on the degree of exposureto wind-driven rain,e.g. brickwork facing theprevailing wind acrossopen ground is moreexposed than brickworkprotected by nearbybuildings.

Sulfate attack occurs only ifunusually high levels of solublesalts are present, e.g.:

• in clay bricks.• in some ground conditions.• in chimney gases.• in clinker and ashes used on

site.

If unusually high levels ofsoluble salts are present andsaturation is unavoidable, therisk of frost and sulfateattack can be minimised byspecifying appropriatecombinations of:

• brick designations.• mortar designations.• sulfate-resisting cement.

Clay brick designations,including frost resistance and

6.4 DURABILITY OF BRICKWORK

TABLE 6.2 Equivalent classifying properties of traditional UKengineering and DPC bricks in relation to BS EN 771-1

Performance characteristic Reference Clay engineering bricks

Class A Class B

Compressive strength BS EN 771-1 �125 �75(N/mm2)

Water absorption (% by BS EN 771-7 �4.5 �7.0mass) and also when (and DPC1) (and DPC2)used as DPC units

Net dry density (kg/m3) BS EN 771-13 �2 200 �2 100

Freeze/thaw resistance BS EN 771-1 F2 F2category

Active soluble salts content BS EN 771-5 S2 S2category

This table is derived from the National Annex to BS EN 771-1.

TABLE 6.1 Durability designations of clay bricks

Designation Frost resistance (see Soluble salts content Section 6.2) (see Section 6.3)

BS BS BS 3921 BS EN 771-13921 EN 771-1

FL F2 Frost resistant (F) Low (L) S2FN Frost resistant (F) Normal (N) S1

ML F1 Moderately frost resistant (M) Low (L) S2MN Moderately frost resistant (M) Normal (N) S1

OL F0 Not frost resistant (O) Low (L) S2ON Not frost resistant (O) Normal (N) S1

This table is derived from table 3 of BS 3921(1).BS EN 771-1 designations have been added.

soluble salt content categories,are set out in table 6.1.

The classification ofengineering anddamp-proof course bricks isset out in table 6.2.

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DURABILITY OF BRICKWORK 177

TABLE 6.4 Durability of brickwork in finished construction (See Figure 6.13)

Masonry condition or situation Brick quality/mortar designation/classification

A Work below or near ground level (if sulfate ground conditions exist – see note[1])

A1 Low risk of saturation with or without freezing FL F2 (i) M12 (ii) M6 (iii) M4FN F2 (i) M12 (ii) M6 (iii) M4ML F1 (i) M12 (ii) M6 (iii) M4MN F1 (i) M12 (ii) M6 (iii) M43–7 (iii) M4 (iv)[2] M2

A2 High risk of saturation without freezing FL F2 (i) M12 (ii) M6FN F2 (i) M12 (ii)* M6ML F1 (i) M12 (ii) M6MN F1 (i) M12 (ii)* M63–7 (ii) M6 (iii) M4

A3 High risk of saturation with freezing FL F2 (i) M12 (ii) M6FN F2 (i) M12 (ii)* M63–7 (ii) M6

B DPCs(if sulfate ground conditions exist – see note[1])

B1 In buildings DPC1 (i) M12

B2 In external works DPC2 (i) M12Note: for classification of DPC bricks see table 6.2.

TABLE 6.3 Mortar mixes and designations

Basic Cement:lime:sand Cement:sand Cement:lime:composition with air-entrainment with air-entrainment sand

Binders Ordinary Portland Masonry cement Masonry cement Ordinary Portland cement cement or sulfate- with high lime with other than or resisting Portland content high lime content sulfate-resisting Portland

Designation cement (1:1 OPC:lime) cement

BS 5628 BS EN 998-2:2003

(i) M12 1:0–1/4:3(ii) M6 1:1/2:41/2 � Air 1:3 1:21/2–31/2 1:3–4 � Air 1:1/2:4–41/2(iii) M4 1:1:51/2 � Air 1:41/2 1:4–5 1:5–6 � Air 1:1:5–6(iv) M2 1:51/2–61/2 1:7–8 � Air 1:2:8–9

– Mortar of high durability – General use mortar of good durability

NOTES:The types of mortars of any one designation are of approximately equal strength. The range of sand proportions is to allow forvarying grades of sand. The second quantity e.g. 1:1:5–6 for designation (iii) is for a well-graded sand. Smaller proportions of sand(or large proportions of cement and lime) are necessary with less well-graded sands (see fig 4.3).The proportions of hydrate limes may be increased by up to 50% to improve workability.With the permission of the designer, plasticisers may be added to lime:sand mixes to improve their early frost resistance. Ready-mixedlime:sand mixes may contain such admixtures. This table is based on information given in Table 14 of BS 5628-3:2001.

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TABLE 6.4 Durability of brickwork in finished construction (continued)


C Unrendered external walls (other than chimneys, copings, cappings, parapets and sills)

C1 Low risk of saturation FL F2 (i) M12 (ii) M6 (iii) M4FN F2 (i) M12 (ii) M6 (iii) M4ML F1 (i) M12 (ii) M6 (iii) M4MN F1 (i) M12 (ii) M6 (iii) M43–7 (iii) M4 (iv)[2] M2

C2 High risk of saturation FL F2 (i) M12 (ii) M6FN F2 (i) M12 (ii)* M63–7 (iii) M4

D Rendered external walls (other than chimneys, copings, cappings, FL F2 (i) M12 (ii) M6 (iii) M4parapets and sills – see note [3]) FN F2 (i)* M12 (ii) M6

ML F1 (i) M12 (ii) M6 (iii) M4MN F1 (i)* M12 (ii) M63–7 (iii) M4 (iv)[2] M2

E Internal walls and inner leaves of cavity walls (where designation (iv) mortars are FL F2 (i) M12 (ii) M6 (iii) M4 (iv)[2] M2used – see note [2]) FN F2 (i) M12 (ii) M6 (iii) M4 (iv)[2] M2

ML F1 (i) M12 (ii) M6 (iii) M4 (iv)[2] M2MN F1 (i) M12 (ii) M6 (iii) M4 (iv)[2] M2OL F0 (i) M12 (ii) M6 (iii) M4 (iv)[2] M2ON F0 (i) M12 (ii) M6 (iii) M4 (iv)[2] M23–7 (iii) M4 (iv)[2] M2

F Unrendered parapets (other than copings and cappings)

F1 Low risk of saturation, e.g. low parapets, FL F2 (i) M12 (ii) M6 (iii) M4on some single-storey buildings FN F2 (i) M12 (ii) M6 (iii) M4

ML F1 (i) M12 (ii) M6 (iii) M4MN F1 (i) M12 (ii) M6 (iii) M43–7 (iii) M4

F2 High risk of saturation, e.g. where a capping FL F2 (i) M12 (ii) M6only is provided FN F2 (i)* M12 (ii)* M6

3–7 (iii) M4

G Rendered parapets (other than cappings and copings) (where sulfate-resisting cement is FL F2 (i) M12 (ii) M6 (iii) M4recommended – see note [3]) FN F2 (i)* M12 (ii)* M6

ML F1 (i) M12 (ii) M6 (iii) M4MN F1 (i)* M12 (ii)* M63–7 (iii) M4

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DURABILITY OF BRICKWORK 179



H Chimneys (sulfate-resisting cement in mortars and renders are strongly recommended due to the possibility of sulfate attack from flue gases)

H1 Unrendered with low risk of saturation FL F2 (i)* M12 (ii)* M6 (iii)* M4FN F2 (i)* M12 (ii)* M6 (iii)* M4ML F1 (i)* M12 (ii)* M6 (iii)* M4MN F1 (i)* M12 (ii)* M6 (iii)* M43–7 (iii)* M4

H2 Unrendered with high risk of saturation FL F2 (i)* M12 (ii)* M6FN F2 (i)* M12 (ii)* M63–7 (iii)* M4

H3 Rendered FL F2 (i)* M12 (ii)* M6 (iii)* M4(where sulfate-resisting cement is FN F2 (i)* M12 (ii)* M6recommended – see note [3]) ML F1 (i)* M12 (ii)* M6 (iii)* M4

MN F1 (i)* M12 (ii)* M63–7 (iii)* M4

I Cappings, copings and sills [7]Cappings, copings and sills except for chimneys FL F2 (i) M12

FN F2 (i) M124–7 (ii) M6

Cappings and copings for chimneys FL F2 (i)* M12FN F2 (i)* M124–7 (ii)* M6

J Freestanding boundary and screen walls (other than copings and cappings)J1 With coping [7] FL F2 (i) M12 (ii) M6 (iii) M4

FN F2 (i) M12 (ii) M6ML F1 (i) M12 (ii) M6 (iii) M4MN F1 (i) M12 (ii) M63–7 (iii) M4

J1 (a) With coping exposed to severe FL F2 (i) M12 (ii) M6 (iii) M4driving rain [5] [7] FN F2 (i)* M12 (ii)* M6

ML F1 (i) M12 (ii) M6 (iii) M4MN F1 (i)* M12 (ii)* M63–7 (iii) M4

J2 With capping [7] FL F2 (i) M12 (ii) M6FN F2 (i) M12 (ii) M63–7 (iii)*[4] M4

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K Earth-retaining walls (other than copings and cappings)

K1 With waterproofed retaining face FL F2 (i) M12 (ii) M6and coping [7] FN F2 (i)* M12 (ii)* M6

ML F1 (i) M12 (ii) M6MN F1 (i)* M12 (ii)* M63–7 (ii) M6 (iii) M4

K2 With coping or capping but no FL F2 (i) M12waterproofing on retaining face [7] FN F2 (i)* M12

4–7 (ii) M6

L Draining and sewerage, e.g. inspection chambers, manholes (if sulfate ground conditions exist – see note [1] )

L1 Surface water Eng (i) M12FL F2 (i) M12FN F2 (i)* M12ML F1 (i) M12MN F1 (i)* M123–7 (ii) M6 (iii) M4

L2 Foul drainage (continuous contact Eng (i) M12with bricks) FL F2 (i) M12

FN F2 (i)* M12ML F1 (i) M12MN F1 (i)* M127[6] (ii) M6

L3 Foul drainage (occasional contact Eng (i) M12with bricks) FL F2 (i) M12

FN F2 (i)* M12ML F1 (i) M12MN F1 (i)* M123–7[6] (ii) M6 (iii) M4

KEY:EN references are in bold.FL, FN, ML, MN refers to clay brick designations, see table 6.1.3–7, etc. refer to classes of calcium silicate bricks, see table 6.3.(i), (ii), (iii), (iv) refer to mortar designations in BS 5628. F0, F1, F2 refer to clay brick durability in BS EN 771-1:2003, table 6.1. M2, M4, M6, M12 refer to mortar compressive strength class in BS EN 998-2:2003, table 6.2.* – sulfate-resisting cement is recommended or advisable.

NOTES:[1] If sulfate ground conditions exist, expert advice should be taken when specifying mortars. Also see cl. 22.4 BS 5628-3.[2] Protect masonry under construction from freezing and saturation.[3] Where sulfate-resisting cement is recommended for use in mortar it should also be used in the base coat of any rendering.[4] Some manufacturers recommend the use of designation (ii) mortars rather than designation (iii) with SRC.[5] For notes on assessing exposure to driving rain see section 6.7, fig 6.46 and text.[6] Some types of calcium silicate bricks are not suitable for use in these situations – the manufacturer should be consulted.[7] For definitions of copings and cappings – see section 5.1.

This table is based on information given in table 13 of BS 5628-3:2001 which specifiers are advised to refer to as the authoritativedocument.

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ALLOWING FOR VARIATIONS IN BRICK SIZES 181

understanding of the natureof size variation as it affectsbricklaying. A morecomprehensive exposition ofthe sophisticated, technicaland statistical manufacturingmethods used to controlvariations in size, includingthe methods of measuringbricks for that purpose,would be inappropriate inthis section.

WHY BRICKS VARY IN SIZEDespite modern manufacturingand quality control techniques,slight variations in raw materialsand firing temperatures, andmould and die wear will causesome variations in sizes withinand between batches of bricks,as do some firing techniquesdeliberately used to producemulticoloured bricks.

HOW BRICKS VARY IN SIZEImagine the length of fiftystandard bricks, sampled froma consignment, being measured

References(1) BS EN 771-1:2003 ‘Specification for

clay bricks’.(2) BS EN 771-2:2003 ‘Specification for

calcium silicate (sandlime andflintlime) bricks’.

(3) BS 5628-3:2001.

6.5 ALLOWING FOR VARIATIONS IN BRICK SIZES

The ‘actual sizes’ ofindividual bricks within abatch, as well as theaverage sizes of bricks indifferent batches, inevitablyvary from the ‘work sizes’*at which the manufacturersaim (i.e. 215 by 102.5 by 65 mmfor standard bricks). Thissection examines briefly thenature of the variations andways of allowing for themin producing attractivefacework.

Only sufficient backgroundinformation is given tointroduce an essential

Figure 6.13. Key to masonry conditions &situations referred to in table 6.5.

KEY POINTS

■ Only saturated brickwork suffersfrost and sulfate attack.

■ Detailing and good site practicecan minimise saturation.

■ The correct combination ofbricks and mortars canenhance the durability ofbrickwork.

Renderedexternalwalls

D

Drainagemanholes,inspectionchambers

G

Renderedparapets

H

C

F

I

I

I

J

B B

K

A L

Copings

Chimneys

Unrenderedparapets

Unrenderedexternal walls

Sills

DPCs

Cappings

Free-standingwalls

DPCs

Earth-retainingwalls

Below or near ground level

*For definitions see section 2.1 ‘Setting-out facework’ fig 2.1 and section 6.10 on‘Brick manufacture’.

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to the nearest millimetre,consistently along the faceor centre line. If the bricks ofidentical length are then stackedin separate piles, with theshortest bricks on the left andthe longest on the right theresult, with say extruded wire-cutbricks, might be as in fig 6.14,while that with hand-madebricks might be as in fig 6.15.

In both examples the bricksthat are work size or very closeto it are in the highest piles,that is to say they occur mostfrequently, while the large andsmall sizes at the extremes are inthe lowest piles and occur leastfrequently. Figure 6.14 depicts acomparatively close distributionof sizes with over three-quartersof the bricks within �1 mm ofthe work size whereas fig 6.15depicts a relatively widedistribution with less than halfthe bricks within �1 mm.

The examples are intendedto illustrate only the nature ofvariations in brick sizes and theyshould not be used to makeunwarranted assumptions. Forinstance, of the fifty bricks, infig 6.15, one is 4 mm more and

another is 4 mm less than worksize. It would be wrong toassume from this that 4% ofbricks in larger consignmentswould have a variation of�4 mm. Finally, the examplesdo not illustrate a recognisedtechnique for establishingconformity with the requirementsof relevant Standards.

LIMITATIONS ON SIZEVARIATION

The European Standards in theEN 771 range have introducedtechniques for measuring bricksthat are better suited to a

laboratory than site. In order tomaintain the simple site teststhat are part of the BritishStandards (e.g. BS 3921), theBritish Standards Institute haspublished a publicly availablespecification BSI PAS 70:2003that deals with the specific issuesof clay brick, site measureddimensions and tolerances, andalso brickwork reference panelsfor appearance purposes.

Use of the PAS 70 techniquesallows site personnel to carryout checks to determine whetheror not bricks are within specifiedlimits. However, it must beunderstood that in case of

215

214

213

212

216

217218

215

214

213

212

216

217218

219211

Figure 6.14. A possible distribution of brick sizes in a sampleof fifty.

Figure 6.15. A wider distribution of brick sizes in a sampleof fifty.

Figure 6.16. (inset)Measuring a singlecalcium silicate brick.Figure 6.17.Measuring 24 claybricks.

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a dispute the more detailedtechniques in the EN 771 serieswill override PAS 70. Whateverlimits and methods ofmeasurement are used, the needfor bricklaying skills to take upvariations in brick sizes within thejoints will remain a fact of life.

HOW ARCHITECTS ANDBRICKLAYERS CAN ALLOW FOR

VARIATIONS IN BRICK SIZESArchitects should, if possible,dimension brickwork in multiplesof whole or half-bricks, tominimise the need for brokenbond and cutting of bricks.Multiples of brick dimensionsare set out in tabular form foreasy reference in BDA DesignNote 3(1).

Architects should also identifyfeatures, such as narrow piers,soldier courses, copings,cappings and sills where brickswith tighter limits of size thanthose specified in the relevantBritish Standard are required.Such bricks may be selected bythe manufacturers beforedelivery or from consignmentsdelivered to site. In both casesinstructions should be givenwell in advance.

It is advisable to warn all themanufacturers where polychromebrickwork is involved so that theycan liaise and minimise any effectof variations in sizes between thedifferent colour bricks.

Bricklayers use their traditionalskills and experience so that,despite variations in brick sizes,the brickwork will have a uniformappearance with cross joints asconsistent as is practicable.

Particular points for botharchitects and bricklayers arelisted below.

Checking deliveriesTake samples of bricks fromdifferent packs, from differentpositions within the packs and invertical slices. Measure all threedimensions. If it is suspected thatthe consignment does notcomply with the limits of size inthe relevant British Standard,first inform the supplier ormanufacturer or both. It isadvisable to have at least one ofthem present when carrying outthe precise conditions of the testdescribed in the relevantStandard.

Blending packs of bricksModern methods ofmechanically handling andtransporting bricks tend to takebricks from one part of the kiln,and therefore of similar actualsizes, and package them inhorizontal layers rather thanblend them as happened whenbricks were loaded andunloaded by hand. Packagedbricks should be blended on site,when ‘loading out’ for thebricklayer, by drawing from atleast three packs at a timepreferably broken downvertically (fig 6.18) (see Sections1.3 ‘Handling, storage andprotection of materials’; 3.2‘Blending facing bricks on site’).

Some manufacturers are ableto blend bricks before they are

packaged, so that extremes ofsizes and variations of colourare distributed more evenly.Even so it may still be advisableto ‘load out’ from three ormore packs. If there is any doubtthe manufacturer should beasked.

Setting-out at ground levelThe first course of brickworkshould be ‘run-out dry’ beforebricklaying begins in order tocheck the size of cross joints.Because the average brick sizemay vary between batches,facework should be set outto the ‘co-ordinating size’,i.e. 4 stretchers to 900 mmrather than attempting tomaintain 10 mm joints.

Plan the location of revealbricks and any broken bond,check bonding arrangements atcorners, angles and attachedpiers particularly if squint or dogleg special shapes or plinthcourses are to be built-in andplan the position of perpends(see Sections 2.1 ‘Setting-outfacework’; 2.4 ‘Verticalperpends’).

This procedure is not a sign ofa bricklayer who lacks skill orexperience but of one who takescare to anticipate and prepare forthe work to hand, the better toexercise his skill and avoid costlymistakes.

Figure 6.18. Anumber of packsopened for ‘loading out’to bricklayers.

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Contrasting bands of differenttypes of bricks (figs 6.19 & 6.20)If, despite the architect’s efforts,bricks for use in contrasting bandcourses have widely differentaverage lengths from those inthe main wall or others in theband, the bricklayer shouldwarn a supervisor of anyanticipated difficulty in avoidingexcessively wide or narrowvertical cross joints in the bands.Architects may decide to usemortars matching the brickcolour to minimise any visualdiscrepancy.

Excessively large or small bricksA few may occur in a batchwhich conforms to the specifiedlimits of size. They should not bediscarded but set on one sidefor possible use elsewhere,e.g. where cut bricks arerequired for broken bond orat openings.

Clay bricks that do not meet theBS limits of sizeSome soft-mud, stock bricks,specified for their wide variationsin colour and texture are notselected before delivery and maynot conform to the EuropeanStandard for limits of size. Theseare often described as ATRsmeaning ‘as they rise’ (fig 6.21)and often, though not always,result from clamp firing

(see Section 6.10 ‘Brickmanufacture’). Unless areference panel has been builtand agreed, bricklayers should,before beginning to lay suchbricks, ensure that theimpossibility of maintainingplumb perpends and 10 mmjoints is appreciated and thatthe result will be acceptable.The architect may require someselection to be made on site(see Section 1.1 ‘Reference andsample panels’).

Soldier courses, arches and brick-on-end sills(fig 6.22)In order to get a straight linetop and bottom, the architectshould have arranged for thebricks to be selected in thefactory by the manufactureror by others on site, typicallyto �1.5 mm. Even so thebricklayer may have to setsome bricks aside in order tomaintain an acceptable linetop and bottom.

Cappings and copings(figs 6.23 & 6.24)An unbonded coping orcapping that has to be aligned

Figure 6.19. Bands of contrastingcoloured bricks at Newnham College,Cambridge. Architect Birken Heywood.

Figure 6.20.Contrasting colouredcourses at PumpingStation, Isle of Dogs.Architect John OutramAssociates.

Figure 6.21. ATRs – not claimed toconform to BS limits of size.

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both sides demands bricks withvery little size variation andinvariably this requires selection,preferably before delivery.Bricklayers may sometimeshave to turn double cant bricksend for end to get the bestalignment of the cant faces ifthey are not a perfect 45°.Similar care must be takenwhen using cant bricks inwindow sills.

Narrow attached piersNarrow piers (fig 6.25) mayrequire some selection ofbricks if the cross joints areto be reasonably uniform inwidth. One-brick piers (fig 6.26)pose special problems as it ispossible to plumb only oneside of the pier and the otherside will vary to the extent ofthe stretcher lengths. Bricklayersshould ask before starting

work whether the variation isacceptable or whether selectionis required.

Reference(1) BDA Design Note 3. Brickwork

Dimensions Tables. A guide todesigning and building to brickdimensions.

Figure 6.22. Soldiercourses. River FlossFlood AlleviationScheme, York.Architects Clouston.

Figure 6.23. A satisfactory double cantbrick-on-edge capping.

Figure 6.24. An unsatisfactory doublecant brick-on-edge capping.

Figure 6.26. One-brick, 215 mmwide pier.

Figure 6.25. Two-brick, 440 mm widepiers.

KEY POINTS

■ Measure all three faces ofa number of bricks fromdifferent packs shortly afterdelivery.

■ Inform the supplier ormanufacturer immediatelyif you suspect they do notconform to the specified limits.

■ Run-out the first course ofbricks dry before starting tobuild.

■ If the building has bands ofdifferent colour bricks, run-outdry adjacent rows of each typeto compare the relative sizes ofthe cross joints.

■ Check bricks to be used insoldier courses, narrow piersand cappings.

■ Draw from at least threepacks of bricks when ‘loadingout’.

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The appearance of brickworkdepends initially on architects’designs but can be realisedonly by competent brickworkteams.

THE ARCHITECT’SREQUIREMENTS

The colour, texture, size andshape of the bricks, the colourand profile of the mortar jointsand the brickwork bond, allaffect appearance. They arenormally chosen by thearchitect.

THE BRICKWORK TEAM’SRESPONSIBILITIES

In fulfilling the designrequirements the brickworkteam, which may include mainand subcontractors, supervisors,bricklayers, mixer drivers and

labourers, is responsible forcompleting many operationsrequiring skill, knowledge,understanding, care andattention.

Good site managementensures that all membersof the team know theoperations for which theyare responsible.

In this section, comments onsixteen operations are groupedunder the main headings thatdescribe those factors thataffect the appearance ofbrickwork.

COLOUR AND TEXTURE OFBRICKS

The choice of colour and textureof bricks is obviously veryimportant.

The brickwork teamhas important but perhapsless obvious responsibilitiesfor:

1. Checking deliveriesCheck that the correct brickshave been delivered, against areference panel if one has beenbuilt (fig 6.27). Reference panelsmay have been built not only toestablish a suitable colour andprofile for the mortar joints butalso to establish the extent towhich colour variations andminor surface blemishes areacceptable. Viewing of thepanel for these purposes isusually done from a distance of3 m (see Section 1.1 ‘Referenceand sample panels’).

2. Storage and protection ofbricksStore bricks to avoid contact withthe soil, contamination by mudand other building materials, andprotect from saturation which cancause staining and efflorescence(see Section 1.3 ‘Handling,storage and protection ofmaterials’).

3. Blending deliveriesUnless bricks have beenadequately blended by themanufacturer before deliverythe brickwork team must doso by loading out from at leastthree packs so as to avoidcolour patchiness or bandingin the brickwork (fig 6.28)(see Sections 1.3 ‘Handling,storage and protection ofmaterials’; 3.2 ‘Blendingfacing bricks on site’). Somemanufacturers recommendloading out from four, five orsix packs, especially for brickshaving descriptions such as‘Multi’, ‘Blend’ or ‘Mixture’.

Particular care should be takenin blending multicoloured brickswhich by their nature vary a greatdeal. In addition, bricklayers,unless instructed otherwise,should select bricks from thestack to ensure that severalbricks of a similar colour are notlaid adjacent in one course orconcentrated in a patch (fig 6.29).

COLOUR OF MORTAR JOINTSAbout one fifth the surface areaof brickwork consists of mortarjoints. As a result the mortar

6.6 APPEARANCE

Figure 6.27. A reference panel.

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APPEARANCE 187

colour profoundly affectsthe apparent colour of thebrickwork. Used deliberately,as an element of design,changes of mortar joint colourcan enhance brickwork (fig 6.30).Unintentional changes causedby lack of skill or carelessnesson site can be visually disastrous(fig 6.31).

The colour of mortar dependsin the first instance on the colourof the cement, sand andpigments, whether or not limeis used and on the proportionsin which these materials arebatched. In addition the watercontent, or consistence, of themortar and the extent of toolingof the joint which brings thelaitence to the surface, allaffect the colour.

The bricklaying team shouldensure:

4. Consistency of supply ofmaterials for mortarsThe colours of sands and evenPortland cements from differentsources vary enough to affectmortar colours and wherecolour consistency is requiredthese materials should alwaysbe obtained from the samesource. Pre-mixed coarse stuffand ready-to-use retardedmortars should also be obtainedconsistently from the samesupplier (see Section 4.1‘Mortars’).

5. Protection of mortarmaterialsMortar materials and pre-mixedmortars must be protected onsite from mud, dirt, oil and otherbuilding materials. Protection isalso needed against the fineparticles of cement, lime and

Protect tops ofstacks from rain –secure protectionfrom being blownaway

Removebanding to asafe place


Remove bricks invertical slices forbest blend


Figure 6.28. Loading out fromat least three packs.

Figure 6.29.Multicoloured bricks –dispersing bricks ofsimilar colour.

Figure 6.30. Intentional decorative useof coloured mortars.

Figure 6.31. Unintentional changes ofmortar colour.

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pigments being washed out bywater. Lack of such protection canresult in mortar colour changes(see Section 1.3 ‘Handling, storageand protection of materials’).

6. Accurate and consistentproportioning and mixingWhether separate materials areproportioned on site, by weightor volume, or whether cementis added to pre-mixed coarsestuff, accuracy must bemaintained (fig 6.32), otherwisebatches of mortar will differ incolour. Always ask the mortarsupplier before adding anythingwhich might affect the colourof the mortar. It may also affectthe strength.

Similarly mortar must be mixedin a consistent way whether byhand or machine in order to avoidcolour variations (see Section 4.1‘Mortars’).

QUALITY OF FACEWORKQuality brickwork is distinguishedfrom that which is merelyadequate by the care with whichfacework is set-out to minimisethe effect of unavoidable brokenbond, to maintain verticalperpends, line, level and plumband regular cross and bed jointwidths. The matters dealt withunder this heading are morefully described in other sections(see Sections 2.1 ‘Setting-outfacework – stretcher half-bond’;2.2 ‘Gauge and storey rods’;2.3 ‘Line, level and plumb’;2.4 ‘Vertical perpends’).

The brickwork team should:

7. Set-out dry at ground levelSet-out brickwork dry at groundlevel, noting the position of

reveals to openings above(fig 6.33). Consult thesupervisor or architect to agreethe position of any unavoidablebroken or reverse bond (fig 6.34)(see Section 2.1 ‘Setting-outfacework–stretcher half-bond’).

Establish perpends at groundlevel and plumb at regularintervals for the full height offacework to avoid the visualdistraction of their wanderingacross the facade (fig 6.35)(see Section 2.4 ‘Verticalperpends’).

8. Lay to the lineBricklaying line should be fineenough for the top arris of everybrick to ‘follow the line’. Eachbrick should be close withouttouching, so that you can ‘justsee the light’ between brick and

line (fig 6.36) (see Section 2.3Line, level and plumb’). Whenlaying some stock type bricks itmay be necessary to modify thenormal technique and allowsome portions of irregular brickfaces to be in front of the linein order to obtain a generallyregular appearance.

Position ofwindow

opening tobe built

DPC

Plumbedperpends ‘Reveal’ bricks

positioned atground level

‘Reveal’

Opening4½ bricks

Figure 6.32.Purpose-made boxesfor accurate gauging ofmortar materials.

Figure 6.33. Setting-out window position at ground level.

Figure 6.34. Broken bond positionedunder window.

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APPEARANCE 189

9. Avoid ‘hatching andgrinning’The lower arris of each brick mustbe bedded flush with the coursebelow. If bricks are laid carelesslyso that the lower arrises are notflush with those below, ‘hatchingand grinning’ will be apparent,particularly when the sun shinesobliquely down the face (fig 6.37).

10. Maintain vertical gaugeWhen raising quoins, maintainconsistent vertical gauging of bedjoints, by the use of gauge and

storey rods (fig 6.38) (see section2.2 ‘Gauge and storey rods’).

11. Rack back whereverpossibleRack back incomplete work andavoid vertical toothing whereverpossible. It is difficult to build on totoothing without the join showingon the facework (fig 6.39)(see Section 2.3 ‘Line, level andplumb’).

12. Lay some stock bricks withextra careWhen laying some soft mud orstock bricks a different techniqueis required from that used whenlaying wire-cut or pressed bricks.

The upper and lower surfacesof the latter are generally at rightangles to their stretcher andheader faces. This will not alwaysbe the case with stock type bricksespecially if they are clamp fired.

When laying slightly distortedbricks to the line, tilt them one

way or the other in order to getthe brick face into the samevertical face plane as the wall(fig 6.40). This means that thetop of the brick cannot belevelled across the wall.

The resulting irregularity of thetop surface will be taken up inthe bedding mortar and beunnoticed in the finished wall.

Failure to modify normaltechniques when necessarycan cause an uneven surface

Figure 6.35. Plumbing perpends at intervals at ground level.

Bricklayer‘sline

Mark every4th or 5thperpend

Brick NOTtouching line

Brick NOTabove line

Figure 6.36. Laying to a line.

Figure 6.37. ‘Hatching and grinning’.

Figure 6.38. Checking gauge.

Building corners –unsatisfactory method

Building corners –recommended method

Repeat

Repeat

Raise corners runin bricks between

Figure 6.39.

Figure 6.40. Laying distorted stockbricks.

Bedding surface maynot be horizontal

Faces ofbricksalignedvertically

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known as ‘hatching andgrinning’ (see point 9).

Unless otherwise instructed,lay hand-made bricks consistentlywith the frog up so that thecreases read as a ‘smile’ on theface (fig 6.41).

13. Work cleanlyAvoid smudging the face of bricksby spreading just the right amountof mortar each time and cleanlycutting off any surplus. Clean offany splashes of mortar and turnback scaffold boards next to thebrickwork at the end of the dayto avoid mortar being splashed byrainfall onto the facework.

When sweeping or removingscaffold boards take care not tospill mortar on the completedfacework.

14. Maintain a consistentjointing techniqueWhatever joint profile and finish isspecified, the techniques of allbricklayers must be co-ordinated toprovide consistency in the type anddiameter and shape of jointer, thepressure used, the angle of strikingand depth of recessing, otherwisepatches or bands of apparentlydifferent coloured brickwork willbe evident (fig 6.42).

Take care that struck perpendsare struck on the same side,

normally the left-hand side ofall cross joints is indented forright and left handed bricklayersalike (see Sections 2.7 ‘Finishingmortar joints’; 2.8 ‘Pointing andrepointing’; 4.1 ‘Mortars’).

15. Protect newly builtbrickworkRain on newly built brickwork cansaturate the mortar and wash outfine particles of cement, lime andpigments, changing the colour ofthe mortar. Worse still, saturationof the brickwork can lead to severelime-staining on both the mortarjoints and the brick faces. Provisionshould be made to protect newlybuilt brickwork (fig 6.43)(see Section 1.2 ‘Protection ofnewly built brickwork’).

Vulnerable corners and revealsshould be protected from impactdamage (fig 6.44). Brickworkfeatures such as projectingplinths should be protected frommortar droppings and damagefrom falling objects (fig 6.45).

SEALANTS TO MOVEMENTJOINTS

16. A wide choice of sealantcolours is available to blend withmortar colours. Ensure that the

sealant used conforms to thespecification but if none existsthat approval is obtained beforeany sealant is applied.

Figure 6.41. Laying ahand-made brick frog upwith a ‘smile’ on its face.

Figure 6.42. Finishing of joints must beconsistent.

Figure 6.43. Protectingnewly built brickwork.

Figure 6.44. Protectingvulnerable brickwork.

Figure 6.45. Plinth, protected frommortar droppings.

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RAIN RESISTANCE OF CAVITY WALLS 191

BS 8104:1992(1). The assessmenttakes into account:

(a) the geographic location of thewall within the UK (fig 6.46a).

(b) the formation of nearby land,including marked changes oflevel (fig 6.46b).

(c) other buildings and treeswhich may shelter the wall;the orientation of the wall(fig 6.46c).

(d) the design of the wall,including height, lengthand protective overhangs(fig 6.46d).

6.7 RAIN RESISTANCE OF CAVITY WALLS

THE BRICKLAYER’SCONTRIBUTION

One of the most commonbuilding defects is rainpenetration causing damageto internal finishes and othervulnerable materials. It usuallyresults from inadequatedesign, workmanship orboth. Remedies are invariablyexpensive and disruptive.

Bricklayers with knowledge,care and skill can maximise theresistance to wind-driven rain ofmasonry cavity walls.

Cavity walls began tosupersede solid walls in the1930s because, when properlydesigned and built, they weremore resistant to rainpenetration. But since the 1970s,the use of cavity insulation hasincreased the risk of rainpenetration and the need forcareful design and workmanship.

DESIGNAssessing exposure towind-driven rainDesigners assess the severityand frequency of wind-drivenrain which a particular wall willhave to resist, by reference to Figure 6.46. Factors considered when assessing exposure to wind-driven rain.

KEY POINTS

■ Check deliveries of bricks forcolour and texture.

■ Blend bricks by loading out fromat least three packs.

■ Ensure consistency of source forpre-mixed mortars and mortarmaterials.

■ Protect mortar materials andpre-mixed mortars.

■ Accurately proportion andconsistently mix mortars.

■ Set-out bond dry at ground level.■ Determine positions of openings,

any broken bond and perpends.

■ Maintain line, level, plumb andgauge.

■ Keep facework clear of mortarstains.

■ Protect newly built brickwork.

YORK

LEEDS

HebdenBridge

1

2

0

35

68

6

4

58

10

a. Geographic location. b. Land formation.

c. Sheltered by other buildings and trees.

Housessheltered bytrees andotherhouses

Houses withlittle protection

Opencountry

d. Design of walls, e.g. height andoverhanging eaves.

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Detailed design and specificationWhen designing details andspecifying materials to meet theassessed exposure, designers referto BS 5628:3(2), which classifiesthe exposure of sites relative tothe severity of exposure and givesguidance on the factors that affectresistance to rain penetration.

But even the best designsdepend on bricklaying skills, care,knowledge and an understandingof those aspects requiringspecial care.

WORKMANSHIPAspects requiring special care(fig 6.47a)Bricklayers have aresponsibility to:

1. Maximise the rain resistanceof the outer leaf.

2. Ensure that wall ties donot transmit water across thecavity.

3. Build-in cavity trays, verticalDPCs and form weep holesto intercept water reachingthe inner face of the outerleaf and drain it to theoutside.

4. Build-in thermal insulationso that it does not provide a

path for water penetrationacross the cavity.

Further detailed requirementsfor care when building cavitywalls are shown in fig 6.47ban described in the rest of thissection.

(1) Outerleaf

(2) Wallties

(3) Cavitytrays andweep holes

(4) Thermalinsulation

With full-fill or no cavityinsulation – a minimum 50 mmcavity between leaves

Clean excess mortar from cavityside of both leaves, especiallyfrom outer leaf when building-in full-fill insulation

Immediately above DPC traysleave cross joints open as weepholes at not more than 1 mcentres but with at least twoabove any opening. Keep themclear of debris. Fit filtrationplugs if required

Minimum 150 mm betweenDPC and ground level

Weep holes every fourthcross joint

Suspend lath to minimisemortar falling downcavity. Remove and clearafter six courses. ‘Ropes’of twisted hessian, about3 m long, may bepositioned above traysand periodically carefullydrawn out through coringholes

Clean mortar droppingsfrom ties and cavity traysas work proceeds.Do not damage trays

Step cavity tray up toinner leaf at least150 mm

Minimum 150 mmbetween DPC andbottom of cavity

Leave shallow space atground level for unavoid-able mortar droppings

With partial-fill cavity insulation –a recommended minimum50 mm residual air space

Avoid protrusions in cavity.Snapped headers, if required,should be purpose-made oraccurately and cleanly cut

Figure 6.47a. Aspects requiring specialcare. Figure 6.47b. Further requirements for care when building cavity walls.

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1. MAXIMISE RAINRESISTANCE OF THE OUTER

LEAF‘. . .by their nature, masonrywalls are not waterproof. . .’(3).The quantity and degree ofpenetration depend largely onthe intensity and duration ofwind and rain.

During light, wind-driven rain,damp patches usually appear first

at the joints on the cavity face(fig 6.48a). When the rainstops they dry out. Afterlonger or more intense periodsof wind-driven rain, the entireface may become wet andeventually water may runfreely down the face (figs 6.48b & c).

Penetration of a leaf built fromlow absorption bricks will

generally occur more quicklythan through one built fromhigh absorption bricks in thesame exposure conditions. Thelatter delays penetration but itwill occur eventually if thewind-driven rain continues longenough for the bricks to becomesaturated. This is often referredto as the raincoat and overcoateffect’ (figs 6.48d & e).

Dampness on innersurface of outer leafmainly at mortarjoints

a.

Damp patchesspreading as leafbecomes wetter

b.

Leaf virtuallysaturated, waterrunning freely downinner surface ofouter leaf

c.

d. The ‘Raincoat’ effect

Rain penetratesmainly throughjoints

Initial fastrun-off

LOW ABSORPTIONBRICKS

Rain eventually penetratesthrough body of brick aswell as joints

Rainwaterinitially absorbed

HIGH ABSORPTIONBRICKS

e. The ‘Overcoat’ effect

Figure 6.48. Stages of rain penetration of outer leaf under increasing conditions of exposure to wind-driven rain.

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Mortar joints are vulnerable.Tests and observations show thatrainwater first penetrates outerleaves in two ways, through badlyfilled mortar joints and fine cracksat the brick/mortar interface.

(i) Partially filled joints. Fillall joints completely. Do notleave a joint hollow bymerely ‘tipping and tailing’the brick end (fig 6.49).Remember, there are sixtycross joints to everysquare metre of wall!

(ii) Brick/mortar interfaces.Once bricks are bedded, donot attempt to adjust theirposition. This can breakthe bond, leaving finecracks for rain penetrationat brick/mortar interfaces.

(iii) Joint profiles. Form jointprofiles as instructed (seeSection 6.9 ‘Bricklaying toolsand equipment’). Mortarjoints that are finished bytooling with the point ofa trowel or a specialjointing iron (e.g. struckor weathered and buckethandle) have the surfacecompressed and themortar pressed intointimate contact with thebricks to give maximumrain resistance (fig 6.50).

Recessed joints allow morerainwater to penetrate theouter leaf than joints withother profiles and should bespecified only in shelteredpositions.

(iv) Mortar mixes. Use thespecified mortar mix; inparticular do not omit limeif it is specified. Lime, beingwater retentive, delaysdrying of the mortar,allowing time for a goodadhesion to take placewhich is considered toimprove rain resistance(see Section 4.1 ‘Mortars’).

2. WALL TIESDo not slope wall ties down tothe inner leaf; position drips inthe centre of the cavity pointingdown; keep ties free of mortardroppings (fig 6.51). Wall tiescan become a major cause ofrain transfer across the cavity:

in any square metre of wallthere will be at least 5 ties,each a potential path for rainpenetration unless built-inproperly (see Section 4.2 ‘Ties incavity walls’).

3. CAVITY TRAYS, DPCSAND WEEP HOLES

(See also Section 4.3 ‘Damp-proof courses’)Cavity trays should be positionedimmediately above anythingwhich bridges a cavity, suchas lintels, support angles andfloor beams (but not wall ties).Their purpose is to drain thewater to the outside via weepholes (fig 6.52).

Bed cavity trays preferably ina single length and extend themup the inner leaf by at least150 mm. Bed the top edge into amortar bed joint or fix flush withthe inner leaf in accordance withthe manufacturer’s instructions.

Figure 6.49. Fill –do not ‘tip and tail’cross joints.

Figure 6.50. Tooling a ‘bucket handle’profile.

Neverslopedown toinnerleaf

Level orslopedown toouterleaf

Figure 6.51.Positioning wallties.

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Lap unavoidable joints instraight lengths, at corners,changes of levels and stop endsby a minimum of 100 mm andbond them with an adhesiverecommended by themanufacturers. The use ofpreformed units at cornersand changes in level avoidsthe need for complex cuttingand folding, which isparticularly difficult on site.Many instances of rainpenetration are traced tolaps which have not beeneffectively sealed.

may be present or introduced ata later date. If no stop ends aresupplied ask a supervisor if this iscorrect, if there is to be no cavityinsulation you may be instructednot to fit stop ends but in thiscase cavity trays should beextended 150 mm beyond theend of lintels.

Form weep holes by leavingopen cross joints at 1 m centresmaximum. Generally, thereshould be no less than two overany opening. If required insertor build-in proprietary plasticformers or fibrous filters at theface of the joints.

Build-in vertical DPCspositioned at the reveals toopenings, so that they are lappedat the top by cavity trays and inturn lap sill DPCs at the bottom.Where cavities are closed projectthe DPC into the cavity by at least23 mm but preferably 50 mm.These matters have been dealtwith in sections 3.3 ‘Externalcavity walls’; 4.3 ‘Damp-proofcourses’.

When building cavityparapet walls take particularcare that the flashings whichmake-good the joint betweenthe tray and the roof finish arecorrectly installed (fig 6.53).Failure to provide asatisfactory junction betweenflashings and DPCs is anothercommon cause of rainpenetration (see Section 5.2‘Cavity parapet walls’).

Stop endVertical DPC

Weep hole

DPCDPC

DPCFlashing

Flashing

Flashinga. Flashing under DPC. b. Flashing over DPC –

possible rainpenetration.

Figure 6.53. Right and wrong ways of positioning DPCs and flashings.

Figure 6.52. Cavity traysand weep holes.

Bed DPCs and cavity trays onmortar to provide a good bondand project them 5 mm beyondor leave flush with the face ofthe brickwork. Never recessand cover DPCs with mortarotherwise the surface of the brickand mortar joint may spall as theDPC compresses under load.Never allow ground-level DPCsto project into the cavities, asmortar can build up and bridgethe cavity.

Securely bond specifiedstop-ends to cavity trays toprevent water running intocavities and any insulation that

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4. THERMAL INSULATIONFix all cavity batts, slabs orboards in accordance with themanufacturer’s instructions andin particular butt the edgesclosely, but do not overlap.Ensure that they are kept freefrom mortar droppings whichcould bridge the cavity and forma path for rain penetration.

Place a temporary protectiveboard on the top edges of theinsulation to prevent mortardroppings collecting and forminga bridge across the cavity. Whenready to continue, remove thetemporary protection and cleanoff any mortar before placingthe next insulation board, slab orbatt (fig 6.54). Do not build-indamaged or wet insulation.

Fix partial-fill insulation slabsor boards securely with properfittings, usually to the inner leaf,so that no part can tilt acrossthe cavity and form a ledge formortar droppings. Do not usethe drips of butterfly ties forthis purpose; they are not largeenough. A 50 mm cavity shouldbe maintained in front of theinsulation.

With full-fill cavity batts takeparticular care to clean excessmortar from joints on the cavityside of the outer leaf. This is easierto do if the outer leaf is built first.Hardened mortar protrudinginto the horizontal jointbetween batts provides a pathfor water penetration (fig 6.55).

For further details includingavoiding cut edges touching theouter leaf, fitting batts over tieswhich do not coincide with jointsbetween batts (see Section 4.4‘Insulated cavity walls’).

FINALLY

Waterproof finishesReliance should not be placed onclear ‘waterproof’ coatings as asubstitute for good design andworkmanship, even though insome cases their use may reducerain penetration for a limitedperiod. There is often a risk thatby reducing the rate of dryingto the outside, the build-up of

water behind the outer face maycause further deterioration suchas frost attack or sulfate attackon the mortar.

Never apply such finishes to anexternal leaf of ‘M’ clay bricks ifthe cavity is filled with insulation.The external finish and theinsulation both greatly reducethe drying rate of any waterentering the inner leaf, whichgreatly increases the risk ofbrickwork deterioration.

References(1) BS 8104:1992 ‘Assessing exposure

of walls to wind-driven rain’.(2) BS 5628-3:2001, cl. 5.5.3.(3) Ibid., cl. 5.5.2.

Figure 6.54. Protecting insulation frommortar droppings with a temporary board.

Figure 6.55. Excess mortar causes rainpenetration at horizontal joint in insulation.

KEY POINTS

■ Fill all mortar joints solidly.■ Do not adjust brickwork after

bedding bricks.■ Form profile of mortar joint as

specified.■ Use only the type of DPCs

specified.■ Bed all DPCs on fresh mortar.■ Project DPCs 5 mm in front

of, or flush with, brickworkface.

■ Do not allow DPC to project intocavity.

■ Step DPC tray at least 150 mmup the inner leaf; build-in or fixtop edge.

■ Leave open cross joints as weepholes at hot more than 1 mcentres.

■ Lap flashings and DPCs correctlyat the junction of parapet wallsand roofs.

■ Build-in wall ties level or slopingdown to the outer leaf.

■ Fix partial-fill slabs or boards toinner leaf with special clips.

■ Keep ties free of mortardroppings.

■ Keep cavities free of mortardroppings.

■ Close butt insulation batts andboards and keep joints free ofmortar.

■ Clean excess mortar from mortarjoints within the cavity.

■ Place a temporary protectiveboard over insulation whenraising walls above.

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READING CONSTRUCTION DRAWINGS 197

Bricklayers, as skilled andresponsible constructionworkers, must be able to readdrawings accurately. Thissection suggests some firststeps towards the developmentof this essential skill. Traineesshould also take everyopportunity to study drawingsand wherever possiblecompare them with a buildingunder construction. Makingdrawings with a drawingboard, T square and scale ruleis the best way for trainees tobecome fluent. That is the wayarchitects learn.

INTRODUCTORY EXERCISE ININTERPRETING TWO-

DIMENSIONAL DRAWINGSCarefully study fig 6.56 andposition appropriate bricksdry. Then try the more difficultfig 6.57. Check the solutionsagainst fig 6.60 on page 199.

6.8 READING CONSTRUCTION DRAWINGS

E E

Cut AA Cut CC Cut BBCut DD

North elevationWest elevationSouth elevationEast elevation

B

A

C DB

C DA

N

B

A C

C D

D

B

A

Plan view from above Plan cut at level EE

Figure 6.56. Assembly of two single-cant bricks drawn to a scale of 1:10.

C C C

B

A

B

50 A

N B

B

A

East elevation South elevation

West elevation North elevation

Cut at AA Cut at BB

Plan viewfrom above

Plan cut atlevel CC

Figure 6.57. Assembly of six standard bricks drawn to scale of 1:10.

H6469-Ch06 9/15/05 1:17 PM Page 197


*NOTE: Thedrawings on thispage have beenreproduced asaccurately as possiblewithin the limitationsof the printingprocess. They shouldnot therefore beused for scalingpurposes.

Bric

k pa

nel 1

:5

Bric

k pa

nel 1

:20

Bric

k pa

nel 1

:50

Bric

k pa

nel 1

:10

Dot

ted

line

show

sou

tline

of

215

× 65

mm

stre

tche

r fa

ce o

f a

bric

kdr

awn

full

size

(1:1

)

Figure 6.58. Brickwork to commonly used scales*.

Devise similar simpleconstructions, make drawingsand check with a tutor.

THE CONCEPT OF DRAWINGTC SCALE

Buildings and parts of them areinvariably drawn to a reducedscale. For instance, a wall 1 m(1000 mm) high may berepresented on a drawing by aline 100 mm long which is atenth of 1000 mm. The ratioof 100 mm to 1000 mm ismore conveniently expressed as1 to 10, and is normally writtenas 1:10 and called ‘the scale’.

Figure 6.58 shows a brickstretcher face 215 mm long by

H6469-Ch06 9/15/05 1:17 PM Page 198


65 mm high drawn full size (1:1)and portions of half-bondedstretcher brickwork to scales of1:5, 1:10, 1:20 and 1:50.

Figure 6.59 shows a gable wallof the house in figs 6.65 & 6.66to illustrate five smaller scales.A scale of 1:100 is commonlyused to show the layout ofspaces or rooms, particularlywithin small buildings likehouses. A scale of 1:200 is oftenmore convenient to show thelayout of larger buildings. A scaleof 1:500 is commonly used forsite plans (fig 6.64) which showjust the outline of buildings inrelation to the boundaries ofthe building site. A logicalprogression of scales wouldinclude 1:1000 and 1:2000 but inpractice 1:1250 and 1:2500 aremore commonly used for blockplans (fig 6.63) as they can bebased on British OrdnanceSurvey maps to these scales.

House gable end1:100

5025

(67

cour

ses)

7415 (33 bricks)

1:2500 1:1250 1:500 1:200

Isometricprojectionof Fig. 6.56

Isometricprojectionof Fig. 6.57

Figure 6.60. The solution of theexercise on page 197.

Figure 6.59. Typical building in commonly usedscales.

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USING SCALE RULESFigure 6.61 illustrates portions ofa typical scale rule used to set outdimensions on a drawing. Scalerules are usually marked witheight different scales, two oneach of four edges using bothsides of the rule.

The dimensions engraved alongthe edges of scale rules are thoserepresented by the scale rule andare not the actual dimensions asare those marked along the edgeof steel tapes and ‘school rulers’.For example on the 1:5 scale thenumbered dimensions 100, 200and 300 mm are marked atdistances of 20, 40 and 60 mmalong the edge of the rule. Notehow a distance of 100 mm canrepresent 100 mm, 500 mm, 2 m,5 m, 10 m, 20 m, 125 m or 250 m.

A special brickwork scale rulehas been developed by the Guildof Bricklayers (fig 6.62). On oneside is set out the length andheight of bricks to scales of 1:20and 1:10 which facilitatesdesigning and drawing tobrickwork dimensions.

Figure 6.61. Eight ratios commonly used on scale rules.

Figure 6.62. A special brickwork scale.

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REPRESENTING THE LOCATIONAND FORM OF A HOUSE BY

DRAWINGSBlock plansThese show the location of thebuilding site in relation toadjacent sites, roads and otherfeatures (fig 6.63). They aregenerally drawn to the scales of1:1250 or 1:2500 which areused for Ordnance Survey maps,although increasingly a morelogical sequence of scales,1:1000 and 1:2000, is beingused.

Site plansThese show the locationof buildings and possiblydrainage, roads, paths andlandscaping in relation to theboundaries of the building siteand setting-out points and areusually drawn at a scale of1:500 (fig 6.64).

Layout drawingsThese show the spaces orrooms within a building usingplans, elevations, sectionsand cuts.

Plans and elevationsThe outside of a house isrepresented in fig 6.65, firstlyby two drawings in isometricprojection. Both are viewsfrom above and from theopposing NW and SEcorners. Architects sometimesproduce isometric or other‘three-dimensional’ drawingsbut more usually provide only‘two-dimensional’ plans(viewed from above) andelevations (facades viewed atright angles).

Figure 6.63. Block plan 1:2500.

Figure 6.64. Site plan 1:500.

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Isometric projections

West elevation South elevation East elevation

North elevation Roof plan

N

Figure 6.65. House exterior represented in three dimensions and by plan and elevations.

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Plan cuts and sections*

Imagine that the roof andceiling are lifted off the walls ofthe house in fig 6.65. It wouldlook somewhat like fig 6.66a,but would be drawn as a FirstFloor Plan (fig 6.66b). If the firstfloor and ceiling are now removedit would look somewhat likefig 6.66c but be drawn as aGround Floor Plan (fig 6.66d).

Vertical cuts and sectionsCutting vertically through thehouse (fig 6.66e) reveals theroof and floor structures andthe partitions which wouldbe drawn as a vertical cut(fig 6.66f). The position atwhich a vertical cut or sectionis taken is shown on the plans.The position at which a horizontalor plan cut or section is taken isshown on the vertical section,often giving the height above adatum level fixed on site.

NOTE TO TUTORS: The house designchosen contains a number ofquestionable features to providetutors with a means of encouragingthe examination and discussion ofthe design as a way of developingthe ability to ‘walk through abuilding’ and visualise spaces andconstruction. For example, whatunusual features does the househave? The living room is on the firstfloor. Describe the route from thefront door to the living room andfrom the ground floor bedroom tothe bathroom. There is also onedeliberate error in the dimensions inFigure 6.66d.

*NOTE: A ‘section’ shows only thosefeatures that are on a plane cutthrough the building. A ‘cut’ shows, inaddition, features beyond the cuttingplane.

Figure 6.66. Plan and vertical sections related to3-dimensional representations by isometric projections.

a. Isometric projectionwith the roof and firstfloor ceiling removed

c. Isometricprojection withthe first floor andground floorceiling removed

b. Plan cut at level AA

e. Isometric projectioncut at CC

f. Verticalcut at CC

d. Plan cut at BB

C

CC

C

A

B

A

B

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100 × 50 woodplate bedded on

blockwork

Cavity wall tiestype & spacing as

specified

DPC tray

Steel lintel

Open cross jointsat maximum1 m centres

DPC

102 facingbrickwork

50 insulation batt

50 air spaceDPC

Open cross joints atmaximum 1 m centres

Lean concrete fill

Joist hanger

100 blockwork

19 plaster

40 screed

125 concrete slab

DPM on blinding

150 hardfill

Concrete trench fill foundations

5025

Top ofplate

2400

Floorbearing

DPC leveland datum

Detail drawingsThese show parts of aconstruction with specificinformation about therelationship of different materialsand components and of joints.The 1:20 section (fig 6.67) is asimplified typical example whichalso illustrates some of thecommonly used symbols andother graphic conventions. Scalesof 1:10 and 1:5 are alsocommonly used.

Figure 6.67. Typical vertical section at a scale of 1:20.

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CONVENTIONS AND SYMBOLSUSED ON DRAWINGS

Knowledge of the fewconventions and symbols belowenable drawings to be morereadily understood. The applicationof some is illustrated in fig 6.67.

Levels and datums

Level on plans.

Level of cutting planes on sections and elevations.

Ceiling height above finished floor level (ffl) – shown on plans.

Bench Mark.

Lines

Break line.

Line of section or cutting plane.

Beyond the cutting plane and visible.

Beyond the cutting plane but not visible.

Viewer’s side of cutting plane and visible.

Viewer’s side of cutting plane and not visible.

Direction of span of floor or roof structure.

DimensionsDimensions are normally shown in millimetres only*. This avoids confusion andthe repetition of units, e.g.

10 not 10 mm 215 not 21.5 cm or 0.215 m 1200 not 120 cm or 1.2 m 21000 not 21 m

*NOTE: When the United Kingdom changed to metric measurement it adoptedthe International system (SI) units which recommends the use of metres andmillimetres. However, many other countries still use centimetres (cm) in addition.

Dimensions are normally written above and in the centre of a dimension lineto be read from the bottom or right-hand edge of the drawing.

Termination of dimension lines Running dimensions.*

Runningdimensions

*NOTE: Running dimensions are a series of dimensions extending from a fixed point, or datum, along a contin-uous line on which each dimension isthe distance from the datum.

NOTE: Only one type of terminationshould be used on a set of drawings.

or

or

or

or

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AbbreviationsSome of the customary and morecommon abbreviations used ondrawings.

al aluminiumBS British Standardc:l:s cement:lime:sandconc concretedpc damp-proof coursedpm damp-proof membraneffl finished floor levelgalv galvanisedgrc glass reinforced cementhw hard woodmax maximummin minimummj movement jointrwp rainwater pipes/s stainless steelsop setting-out pointsvp soil & vent pipeu/s underside

USE AND CARE OF DRAWINGSON SITE

One person on site shouldbe responsible for thesystematic receipt, recordingand storage of drawings. Inparticular:

(a) Record the numberand date of eachdrawing and amendmentissued.

(b) Withdraw or marksuperseded drawings.Always ensure work iscarried out to the latestamendments.

(c) Store where they willbe protected andso that particulardrawings can be readilyretrieved.

(d) Do not leave drawings indirect sunlight or they willfade.

In addition all users should:

• Set-out and buildonly from dimensions, neverby scaling from a drawing. Ifvital dimensionsare missing ask forinstructions.

• As soon as possiblecheck all dimensionsrelevant to the buildingoperations for whichyou will be responsibleand if there are anyapparent errors orinconsistenciesask for instructions.

KEY POINTS

■ Select drawing required,consulting index if available.

■ Ensure it is the latest amendedversion.

■ Get an overall picture firstbefore looking at details.

■ Read information panels.■ Check that the sum of

intermediatedimensions equals the overalldimension.

■ Do not scale from drawings.■ Take every opportunity

to compare drawingswith the current construction.

Steps and gradientsDirection of RISE of stairs, stepsor ramp

Straightstair/steps

Brickwork

Blockwork

Screed

Concrete

Subsoil

Hardfill

Thermal insulation

NOTE: The numerals represents risers nottreads. There is always one tread less thanrisers.

Symbols of hatching for materials

Title and information panelsThe following typical drawing titleand information panel depicts theinformation normally included.

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BRICKLAYING TOOLS AND EQUIPMENT 207

A bricklayer’s varied kit oftools and equipment must beused correctly, safely, andmust be well maintained, inorder to produce high qualitybrickwork without wastingtime and effort. This sectiondescribes their use and care.

BEDDING AND FINISHINGTOOLS

Brick trowelsA variety of shapes, weights andlengths from 230 mm to 330 mm,are used for lifting and spreadingmortar, removing the excess,finishing joints and rough cuttingbricks (fig 6.68).

• The largest may be preferredfor building walls one-brickthick and more.

• Small trowels arerecommended for intricatework.

• They are manufactured‘handed’ left or right,although modern trowelsoften have both edgeshardened for rough cutting.

• Choose one that has the rightweight and balance for you.Do not assume that thebiggest will be best.

Grip the trowel firmly withthumb on the ferrule, cut, roll,lay and spread the mortar to anominal 10 mm thickness.

• Do not overload the bedjoint. This most commonmistake by trainees wastestime and mortar and stainsthe brick face.

• Position the brick, press downthen run the slightly inclinedtrowel blade along the bedjoint cutting the excessmortar cleanly and use for thenext cross joint (fig 6.69).

• When rough cutting neverplace your thumb on the sideto be cut.

Clean in water daily or, in hotweather, at end of a shift.

• Remove build-up of mortarround the shank with adiscarded piece of soft brickor emery cloth.

• Do not constantly tap bricksdown on the bed with theend of the handle or it willbecome burred anduncomfortable to use. Metalcaps on the end of the trowel

handles can damage brickfaces.

Pointing trowelsThese are obtainable from 175 mmdown to 75 mm long. The latter isoften termed a ‘dotter’ or dottingtrowel and is used to fill and pointcross joints.

Jointing toolsSpecial irons are obtainable forforming half-round tooled jointsbut a piece of hose of suitablediameter, a piece of wood oreven a portion of a discardedbucket handle are used. Butbeware, a black rubber hose maycause staining of mortars. Keepthe jointer flat (fig 6.70). Usingonly the tip causes ‘ribbing’marks (fig 6.71). ‘Tracking’ iscaused if the jointer does notcover the width of the joint,

6.9 BRICKLAYING TOOLS AND EQUIPMENT

Figure 6.71. Using jointer incorrectly.

Figure 6.68. A variety of trowels.Figure 6.70. Using jointer correctly.

Figure 6.69. Removing excess mortar.

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either because it is too small forthe joints or is not pressed in farenough.

Patent tools, having wheels,for moving freely over thebrickwork, and interchangeableheads for forming recessed jointsare known to bricklayers as‘chariots’ (fig 6.72). Use anappropriate width head to avoidtracking or damage to arrises.

Various patterns of ‘chariot’jointing tools are available. Theones illustrated in figs 6.72 &2.60 are typical.

Wash all jointing tools daily ormore often in hot weather.

BrushesSoft brushes are suitable forremoving ‘crumbs’ of mortar afterpointing or jointing. Use stiffbrushes for removing mortar fromrecesses after raking or cuttingout old mortar in repointing work.

Use dry brushes, as wet onessmear. Do not brush before themortar is firm or use excessivepressure. Both can leave brushmarks or smears (see fig 2.76 inSection 2.8 ‘Pointing &repointing’).

Wash brushes daily and allowto dry. Replace when worn.

TOOLS FOR CHECKING ANDALIGNING

Plumb RulesThese have been superseded byspirit levels, but are still useful forchecking the accuracy of spiritlevels.

Spirit levels (fig 6.73)1200 and 900 mm long levels ofaluminium, plastic or hardwoodare most commonly used, but600 mm levels are used in

restricted spaces and 250 mmboat levels for intricate work.

• Never use a hammer on alevel to knock bricks intoplace.

• Clean daily, especially thebubble glass which tends to‘film over’.

• Check accuracy regularly byreversing the level on thesame position or against aplumb level and adjust orreplace bubble vials ifinaccurate.

• Protect hardwood fromwetting and swelling withboiled linseed oil.

• Take particular care of levelswhen working and travelling.

Lines and pinsUse hardened steel pins forsecuring building lines tobrickwork joints. Cheap pinsbend when being hammered in.

Building line is available inmany materials.

• Polyester lines are brown ororange colour. They are cheapbut fray easily.

• Hemp lines are traditional, canbe spliced if they break butare prone to rot in damp toolbags. They are heavy and tendto sag over long distances.

• Cotton lines are similar tohemp but cannot be spliced.

• Twisted nylon lines are tough,tend to twist, fray and cannotbe spliced.

• Woven nylon lines are tough,durable, do not sag greatlyover long distances butstretch a lot.

• Most bricklayers prefer nylonlines.

• Put hitches into a line atregular intervals to preventcomplete unwinding shouldthe pin fall.

• After re-winding the line, tie ahitch on each pin to preventits unravelling in the tool bag(figs 6.74a, b & c).

• In wet weather open weavelines on pins so that they dryout quickly (fig 6.75).

Corner blocksCorner blocks can be quicklymade from scraps of timber,or plastic ones may be bought(figs 6.76 & 6.77).

• Thoroughly ‘wind on’ theline to the block as shownin fig 6.77.

• Keep blocks together in thetool bag with an elastic band.

Figure 6.72. A ‘chariot’ in use.

Figure 6.73. Various spirit levels.

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Steel squaresSteel squares are particularlyuseful for checking thesquareness of piers. They shouldbe wiped clean daily.

Tapes, rules, pencils• Steel tapes are compact and

long but get full of grit.

• Steel tapes should be wipedclean daily and refilled whenworn or damaged.

• Folding rules are shorter andmore rigid but get troddenon. It is a matter of personalchoice.

• A pencil is essential formarking perpends but takecare in use as pencil marks onsome facing bricks aredifficult to remove. A 2Hpencil lasts longer than anHB (see Section 2.1 ‘Setting-out facework’).

CUTTING TOOLS

Club hammers (fig 6.78)Sometimes known as lumphammers, are available in 1 kgand 2 kg weights for use withcold chisels and bolsters. The1 kg hammer is better for mostwork.

Do not hit bricks and blockswith the end of the handle northe faced sides with the hammerhead. The former will burr thehandle and be uncomfortable,the latter will damage the face ofbricks and blocks.

• Wipe hammers dry daily.• Check head regularly and

if loose remove wedges,re-wedge handle or fix a newone. As a temporary measureonly, soak in water to tightenhead.

AN AWFUL WARNINGNever hit two hammer headstogether to hear the ring orfeel the bounce. Sharp piecesof metal can fly off at greatspeed, severely slicing anybody they hit.

Cold chisels and bolsters(fig 6.79)Plain chisels 15–28 mm wide by250 mm long and bolsters50, 75 and 100 mm wide areavailable.

Figure 6.74a. Lift.

Figure 6.74b. Twist.

Figure 6.74c. Tighten.

Figure 6.75. Open weave of line on pins.

Figure 6.76. Wooden corner block.

Figure 6.77. Plastic corner block.

Figure 6.78. Club, brick hammers andscutches.

Figure 6.79. Bolsters and club hammer.

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• The 100 mm bolster is bestfor cutting bricks.

• Comb chisels, similar to ascutch, are useful for chasingor trimming existing walling.

• Plastic mushroom sleeves maybe fitted to most chisels toreduce the risk of injury to thehand.

Wear eye protectors, hold clubhammer firmly at end of handle,not halfway. Position the chiseland, for maximum accuracy,swing the forearm only, not thewhole arm. When cutting bricksdo not hit too hard, firm lighttaps are sufficient and cause lessdamage if you miss (fig 6.80).

All cold chisels should be keptsharp, preferably in a metalworkshop where they can betempered. The opportunityshould be taken to removeburred or mushroomed headswith a grindstone.

Brick hammersA brick hammer has a chiselblade at one end for cutting anda square end for knocking innails (fig 6.78 second from left).

It is particularly useful for roughcutting hard bricks where atrowel would be too light andmight be damaged.

Take care as for a clubhammer, but in addition have thechisel end sharpened andtempered regularly.

Scutches (fig 6.78)A scutch may have two groovedends to receive replacement steelblades or replacement combs fortrimming or cutting. Alternativelythey may have one end groovedand the other square like a brickhammer. The blades are simplyknocked out sideways andturned round or replaced asnecessary.

Care for them as for a brickhammer, but no sharpening isrequired.

Keeping tools togetherConsider storage arrangementsfor care and security, includinglocking of vehicles, a tool lockup, and a canvas bag for theday’s needs. The disadvantagewith a bucket for this purpose isthat during a heavy shower youcollect water.

ADDITIONAL EQUIPMENT FORBRICKLAYERS

Patent metal corner profiles(fig 6.81)These can be obtained in sets oftwo or more, marked with thestandard vertical gauge.They are quickly bolted inposition with the lines held bysimple sliding clips which can beraised as each course is built.

• No quoins, as described insection 2.3, are necessary.

• Profiles are particularlyeffective when building withirregular bricks such as handmade and soft mud brickswith which the building ofcorners is difficult.

• All bricks are laid to the line,and a spirit level is requiredonly to check that the profilesare plumb, which should bedone regularly.

• If the permanent gaugemarkings are unsuitable for aparticular job, mark out therequired gauge with maskingtape and remove at end of job.

Lock away at night for safety.

• Do not mishandle or leavelying about as they becomeuseless if bent.

• Clean daily, especially anymortar around the screwthreads. Oil the latter weekly.

Patent profiles of various effectivedesigns are produced by differentmanufacturers. The tool illustratedin diagrams in this book is onlyintended as a typical example andno inference should be drawn thatthis particular design is approvedor preferred by the authors.Figure 6.80. Cutting a brick.

Figure 6.81. A corner profile setup.

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Some other designs haveadditional features and/oraccessory fittings that extendtheir usefulness in assistingaccurate and well controlledbricklaying.

Tungsten tipped hand sawsThese are used for cutting outbricks from existing walling toform toothings, providing thathard, cement-rich mortars havenot been used. Hand saws areoften preferable as they arevibration free and quiet but takelonger than mechanical saws(fig 6.82). They are useful forcutting lightweight blockworkparticularly up a gable as theyrequire no power or trailingleads.

Avoid hard materials which canknock out the teeth.

• Start gently with small cuts toa depth of 10 mm as theyhave large teeth and are liableto jump.

• When nearly through, slowdown and catch the off-cut,especially if working onscaffolding.

Electric saws with tippedreciprocating bladesDeveloped from wood cuttingsaws to cut concrete blocksquicker, they require a 110 voltpower supply and hence havetrailing cables.

Wear goggles against flyingparticles. It is a dust freeoperation and does not require amask.

Small angle grindersThis normally has a 100 mmdiameter masonry cuttingblade and is commonly used toremove existing mortar beforerepointing.

• Wear goggles and maskagainst dust.

• Wear gloves against abrasivegrit particles.

• Wear ear protectors especiallyin confined spaces.

• Use correct blade i.e. siliconcarbide type abrasive notaluminium oxide.

• It is most important to ensurethat the speed on the bluelabel matches the maximumspeed of the angle grinder.

• Unplug the machine beforefitting a new blade.

• Fit the blade correctly andsecure tightly.

• Ensure that the electricalsupply is not a hazard to theoperator or others.

• Do not use above shoulderheight. Keep away from body,preferably at arm’s length.

• Position guard to deflectparticles from face.

• Make sure that the wheels onall portable machines arereinforced to preventbreaking up under centrifugalforce.

• When cutting small units likebricks and tiles provide astop to restrain the brickwhen the blade is applied.A batten nailed to a boardwill suffice.

• Do not start with blade incontact with unit, it may

snatch and throw the unit oryou off balance.

• Hold the unit firmly,preferably with a cramp.

• Operate in a place free ofpassing people and debrisunderfoot.

• Never put an angle grinderdown until the blade stopsspinning.

NOTE: A safer and more accurate wayof cutting small units is on a masonrybench saw.

Masonry bench saws (fig 6.83)They may be electric or petroldriven and consist of:

• A powered cutter moved byhand, treadle or both.

• A moveable trolley on railswith a stop and sometimes anadjustable stop for angle cuts.

• A water supply pumped tothe blade for dust control(see Section 2.5 ‘Cuttingbricks’ for operatinginformation).

Figure 6.82. Using hand saw.

Figure 6.83. (see also Figure 2.48)Bench saw.

Larger portable angle grinders(fig 6.84)Capable of taking larger bladesfrom 200–300 mm.Used for:

• Cutting masonry units.• Chasing walls for services.

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• Cutting holes for openings orfor toothing block walls.

• The deeper the cut the largerthe blade required.

• Machines for large blades areheavier and less manoeuvrable.

• A person changing theblade on a machinecapable of taking a bladeexceeding 235 mm musthave attended an abrasivewheels training course.

• Beware of ‘snatch’ when firststarting large machines.

• Where a neat straight cut isrequired fix a guide to thewall. Set the batten so thatthe guard, not the blade, runsagainst it to avoid cutting thebatten.

SAFETYBuilding sites are dangerousplaces and bricklayers’ bodies asliable to serious injury asanyone’s. It is common sense tobe constantly aware of this andtake precautions.

EyesKeep goggles hung round theneck ready for use when cutting.When using mechanical plant ahelmet and visor are advisable.

Heads and enclosed brainsSince 1st April 1990 everyone onconstruction sites has beenrequired by law to wear helmets.Adjust the back strap to keepthem on when bending forward.Alternatively fix a chin strap.

Feet, toes and anklesWear safety boots with steel toecaps to support ankles andprevent broken toes.

HearingWear ear protectors when usingnoisy tools and plant.

LungsWear respirators or masks wheredust is generated, especially inconfined places.

Skin and flesh – infection andabrasionRegular contact with cement orlime can cause allergic reactions.Cuts from sharp and abrasivematerials can infect the flesh.Get immediate First Aidattention to clean and cover cuts.Wear barrier cream and/orgloves.

First-aid kitsEven though these are kept onsites it makes sense forbricklayers to carry their ownsmall kit or at least someadhesive plasters.

Figure 6.84. Angle grinder.

KEY POINTS

■ Use only the correct tool for thejob. Ensure that it is in a safecondition.

■ Use all tools correctly to producequality work efficiently and safely.

■ Clean and dry tools daily,sharpen as necessary.

■ Replace all tools if they becomeinefficient or unsafe.

6.10 BRICK MANUFACTURE

Bricks have been made inmany parts of the world forthousands of years. At first,clay was moulded and dried inthe sun. Eventually, brickmakers learned to makeharder more durable bricks byfiring. In recent times, sand

with lime and rock aggregateswith cement have been used(fig 6.85).

During the last 25 years brickmaking has changed frombeing predominantly manualto being highly mechanisedusing modern technology.

In this way bricks remaincompetitive in terms ofappearance, performance,productivity and fuel efficiency.

This section aims to providean understanding of how thephysical and chemicalproperties of bricks, like

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BRICK MANUFACTURE 213

strength and durability aswell as appearance, dependmainly on the type of clay orother material and themethod of manufactureused. But it is not possible,simply by reference to thetype of materials andmanufacturing methodsused, to predict a brickscharacteristics. Instead it isnecessary to understand thevery precise terminologyused to describe them.Nor is it practicable formanufacturers, using agiven brick material andmethod of manufacture, tochange the physical propertiesfrom those established by testand declared in theircatalogues.

BRICK STANDARDS,CLASSIFICATION AND QUALITYUnder the European StandardsSpecification manufacturersdeclare physical propertiesof their products as a resultof a standard testing regime.

The following are some ofthe physical propertiesdetermined by the tests.

Compressive strengthMeasures the resistance tocrushing of bricks, expressed inNewtons per square millimetre(N/mm2) and may range from10 to well over 200 N/mm2 fordifferent types of bricks. Theinformation is used by engineersto calculate the strength ofstructural brickwork. It is also aproperty used to classify classesof clay engineering bricks andclasses of calcium silicate bricks(see Section 6.4 ‘Durability ofbrickwork’). Compressivestrength is not in general anindication of the frost resistanceof a clay brick.

Water absorptionMeasures the increase inweight, expressed as apercentage, of a brick whensaturated, compared with thesame brick when completelydry. The water absorption ofthe most dense to the leastdense bricks ranges from lessthan 4.5% to over 30%.Water absorption is a propertyused to classify clay engineeringand DPC bricks (see Section6.4 ‘Durability of brickwork’).Water absorption is not ingeneral an indication ofresistance to frost attack orresistance to rain penetration(see Section 6.7 ‘Rain resistanceof cavity walls’).

Resistance to frost attackFrost resistance is determinedby a laboratory test that exposesthe brick to a number offreeze–thaw cycles. Bricks aredeclared to be suitable for F0passive exposure; F1 moderateexposure; F2 severe exposure(see Section 6.2 ‘Frost attack’ andSection 6.4 ‘Frost resistance and

durability of brickwork’).The frost resistance of claybricks is not, in general, relatedto either compressive strengthor absorption.

Soluble salts contentThe active soluble salts content isdeclared as Low (S1) or normal(S2) (see Section 6.4 ‘Durabilityof brickwork’).

Clay engineering bricksHave high strength and lowwater absorption and areclassified as Class A andClass B. They are notnecessarily manufactured tothe standard of facing bricks(see Section 6.4 ‘Durability ofbrickwork’).NOTE: there is no standardclassification for the so-calledsemi-engineering brick.

Clay damp-proof course (DPC)bricksAre low absorption brickssuitable for use as DPCs(see Sections 6.4 ‘Durability ofbrickwork’ and 4.3 ‘Damp-proofcourses’).

Facing unitsAre manufactured to give anattractive and consistentappearance.

Common unitsAre suitable for generalconstruction work wheretheir appearance isunimportant Bricks rejectedfrom other grades may beclassified as such.

Recommendations for use ofbricks of particular propertiesfor particular applications aremade in the Code of Practicefor masonry BS 5628-3(1).

91% Clay

7% Concrete 2% Calciumsilicate

Figure 6.85. Relative numbersof bricks made in the UK.

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Standard and special shapes andsizesThe vast majority of bricks aremanufactured to the work size215 mm � 102.5 mm � 65 mm(see Section 2.1 ‘Setting outface work’). However, the specificwork sizes of masonry units arenot standardised on a Europeanlevel. BS 4729(2) defines theshapes and sizes of non-rectilinearbricks that are used to formangles, curves, features and otherconstruction details which cannotbe achieved satisfactorily withstandard bricks (see Section 2.9‘Bricks of special shapes andsizes’).

VARIATIONS IN BRICK SIZESEven with the best qualitycontrol there remain slightvariations in raw materialsand manufacturing processes –after being formed bricksshrink during drying, firing,autoclaving and curing.Consequently, the ‘actual’ sizesof bricks made to a BritishStandard are permitted to varyfrom the ‘work sizes’ within limitsspecified in the standards(see Section 6.5 ‘Allowing forvariations in brick sizes’).

Quality controlDuring the 1980s the majorityof brickworks achieved andhave maintained accreditationto BS 5750(3) (ISO 9000/EN29000) ‘Quality ManagementSystems’. This means that thefactory management systemhas been independentlyassessed to conform to thestandard which covers everyaspect of the manufacturingprocess from raw materials todelivery of the finished bricks.

CLAY BRICKSRaw materialsBrick clays are relativelysoft sedimentary rocks knownby names such as clays,shales, mudstones and marls.Clays are plastic, i.e. they arereadily moulded to a givenshape which will beretained. But adequateplasticity of excavated clay isfrequently only developed bycrushing, grinding and mixingwith water.

Brick clays consist largely ofquartz and clay minerals.The latter, being amongstthe finest particles, areresponsible for the plasticity.

Brick clays are convertedinto hard durable bricks byfiring. At the highesttemperatures of 900°C–1250°Cin the firing process, partialmelting or vitrification of thecomponents of the clayminerals occurs. On coolinga glass develops which binds thematerial together.

Because brick clays shrinksignificantly on both dryingand firing the process iscontrolled to minimise cracking

and variations in the sizes offinished bricks.

Inert minerals, like quartz,help to prevent excessiveshrinkage during drying andexcessive melting andshrinkage during firing.Other minor constituentsof the clay mineral, e.g. sodiumand potassium, assistvitrification.

Iron compounds, e.g. ironoxide as haematite, areresponsible for the predominantred fired colours.

Many other minerals likecarbonates, e.g. limestone,chalk, dolomite; soluble salts,e.g. calcium sulfate as gypsum;and carbonaceous materials,e.g. coal, lignite, may wellaffect the characteristics of thefinished bricks andmanufacturers have tocontrol them.

Table 6.6 lists the keybrick manufacturing claysused in the UK and theirlocations.

Most clays are sufficientlysoft to be excavatedmechanically withoutblasting. Selection of the mostappropriate equipment willdepend on the characteristicsof the deposit and themethod of working thequarry face.

Many manufacturers buildstockpiles to avoid thedifficulties of moving vehiclesin wet clay during winter.

Working methods dependon the characteristics ofeach deposit and the needfor the clay fed to the brickplant to be consistent andpredictable.

Clays, being sedimentary,occur in layers. Where materials

Facingbricks 71%

22% Commonbricks

7% Engineeringbricks

Figure 6.86. Relative numbers of brickscurrently produced in the UK.

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of different characteristics arebeing combined in the sameclay mix, it is common practiceto build a layered stockpile(fig 6.87) which may containsufficient raw material for aperiod of 12 months. Whenclay is removed for delivery tothe brick plant a full vertical cutis taken from the face.

Clay preparationThe aim of clay preparation is todeliver to the shapingmachinery a body of clayconsistent in content, grading,plasticity and water content. Ifthe clay feed varies, so will thefinished bricks.

A sequence of machinesgrind and work the clay to

obtain plasticity and uniformworkability to suit the shapingequipment. Coarse clay iscrushed, ground, rolled, cut,kneaded, etc. with appropriateadditions of water ready forthe forming machine.

Primary crushing reduceslarge pieces to 75–100 mm.

The dry pan mill (fig 6.88)is widely used for secondarygrinding between heavylarge diameter rollers andplates. The largest particles arenow typically 3–5 mm indiameter.

The grinding process yieldsa range of particle sizes toachieve the required packingdensity and porosity. Thefineness of grinding influences

not only the internal andexternal textures of bricksbut also characteristics suchas strength, durability andwater absorption. The effectof particle size on appearanceis particularly evident indragfaced products.

MixingAfter grinding, the moisturelevel is increased for forming.The clay body is worked tomake it homogeneous, withthe water evenly distributedthrough the clay particles.

The double shafted mixer isthe most widely used forplastic clays. Two horizontalshafts fitted with overlappingknives rotate in oppositedirections. The clay is cutand kneaded as it is drivenfrom one end of the mixer tothe other.

AdditionsMaterials to produce throughcolours (e.g. manganese dioxideto produce brown or grey bricks)are usually added at the mixingstage.

TABLE 6.5

Age (millions of years) Environment of deposition Areas used for brickmaking

Boulder clay �1 Glaciers & rivers N EnglandBrickearth �1 Land S E EnglandReading beds circa 65 Deltas S EnglandGault clay circa 90 Marine S E and East AngliaWeald clay circa 130 Deltas/lakes S E EnglandOxford clay circa 160 Marine Central/East AngliaKeuper marl circa 180 Salt lakes MidlandsEtruria marl circa 270 Fresh water MidlandsCoal measure shales circa 310 Deltas and swamps S Wales, Midlands, North ScotlandCoal measure fire-clays circa 310 As above As aboveCulm measures circa 310 Marine S W EnglandDevonian shale circa 390 Marine S W England

Figure 6.87. A layered stockpile. Figure 6.88. A dry pan mill.

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More substantial additions of,for example, sand or coke aresometimes made to controlshrinkage, act as a fuel orgenerate a specific appearance.These are generally incorporatedinto the clay mix via feeders priorto the mixing stage.

ShapingThe forming processes used tomanufacture the majority ofbricks in the UK fall into threecategories: soft mud moulding byhand or machine; extrusion/wire-cut; semi-dry pressing.

The clay bodies used for eachprocess are characterised byfundamentally different moisturecontents and workabilities.

Shrinkage occurs from the wet(formed) through to fired stagesof brick production. Bricks are,therefore, initially formed largerthan the intended work size.

Soft mud moulding to producestock bricksTHE TRADITIONALHANDMAKING PROCESSThe handmaker forms a roughlyshaped clot from a mix of a softmud consistency (greater than20% moisture). The clot is coatedwith sand and thrown into amould, generally precoated withsand (fig 6.89). The bottom ofthe mould is formed by the stock.A kicker may be placed on thestock to form the frog. The stockgives its name to soft mud sandmoulded bricks whether hand ormachine made. The thrown softplastic clot adopts the generalshape of the mould and thecrease patterns characteristic ofthese products and known as‘the handmaker’s walk’.

The sand coating of the mouldallows release of the brick from

the mould for drying. Soft mudbricks are too soft to stack aftermoulding and are driedindividually on pallets.

Frogs assist forming, dryingand firing.

MACHINE MOULDINGMachines for moulding stockbricks have outputs as highas 22,000 bricks per hour.A practised handmaker maytypically make around 100 bricksper hour.

In the standard process, a claymix of soft mud consistency isforced through steel dies by spiralshaped blades into sandedmoulds (fig 6.90). Brick faces aresmooth rather than creased.

A development of thestandard process machinesthrows sanded clots of claysimultaneously into a series ofmoulds. The configuration ofeach clot is different and thesanding varies continuouslyso that no two bricks areidentical. This close simulationof hand throwing createscrease patterns on the brick faces.

‘Slop moulded’ or waterstruck’products are also manufacturedfrom a soft mud mix. Releasefrom the mould is facilitated bywater rather than sand giving adifferent and characteristicsurface texture.

Extrusion/Wire-cutIn the UK this methodaccounts for around 40% ofproduction.

A plastic clay mix is driventhrough a die with a screw.A continuous column isformed with a cross sectionbased on the 215 � 102.5 mmdimensions (fig 6.91). Themoisture content of the clay Figure 6.91. An extruder and column.

Figure 6.90. A soft mud brick machinewith an output of 6,000 bricks per hour.

Figure 6.89. Throwing a brick by hand.

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body is generally in the range of15–20%. Outputs of 20,000bricks per hour can be achievedthrough a single die.

The perforations in extrudedbricks are formed by core bars inthe die head. The size andnumber of perforations vary fromworks to works but, in the UK,do not exceed 25% of the totalvolume of the brick. Perforationsreduce drying and firing costsand incidentally reduce theweight.

Surface texturing to generaterustic, brushed, dragwire, rolledor sanded finishes is carried outimmediately after extrusion.Colours may also be added atthis stage by stains applied withthe sand or via a spray.

Next, the column is cut into aslug which is cut into bricks via amultiple wire cutter (fig 6.92).

Semi-dry pressingThe semi-dry pressing process isused to form Fletton bricks,accounting for a significantproportion of the UK brickoutput. The term ‘semi-dry’refers to the workability of theclay which has a naturalmoisture content of around17–20%. A fine granularmaterial is produced by grindingthe raw clay and pressing the

ground material into brickswithout reducing the naturalmoisture content.

Compaction is by directapplication of pressure in amechanical press (fig 6.93).This helps to developmaximum consolidation andcompaction of the clay.Fletton bricks have frogspressed into them to assistthe drying and firing of thebricks.

Semi-dry pressing requires theminimum amount of moisture forany particular clay and so dryingcosts are reduced.

Other forming methodsStiff plastic pressing involves acombination of extrusion to forma roughly brick-shaped clot andthen pressing in a mould.

Extruded wire-cut bricks maybe repressed to obtain aparticular surface finish orchamfer, etc.

Handling and settingAfter being formed, bricks aredried to specific moisture levelsand set in appropriate patternson kiln cars or static hearthsready for firing.

The bricks are moved andhandled increasingly bymechanisation in order tomaximise productivity (fig 6.94).

Some bricks, like stiff extrudedwire-cut bricks and Flettons, canbe set directly into firing patternsonto a kiln car, by hand or bysetting machines, for drying andfiring without an intermediatehandling stage.

DryingThe drying of clay bricks istechnologically complex andimportant for two reasons:

• The shrinkage which takesplace (5–14% depending onthe clay and moisture

Figure 6.92. A typical multiple wirecutter. Figure 6.93. A semi-dry brick press.

Figure 6.94. Extruded bricks beingmarshalled onto pallets ready for drying.

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content) can cause cracking ifthe process is not effectivelycontrolled.

• The energy used may be asmuch as 30–50% of the totalrequirement. Efficient use ofenergy is essential to minimisecosts though much of theheat may be in the form ofhot air transferred from thekiln to the dryer.

FiringFiring imparts colour, strengthand durability to bricks. As it is asignificant cost in terms of fuelconsumed, energy efficiency is ahigh priority. Firing is carried outin a range of types and sizes ofkilns, depending on the outputrequired and the type of product.

Kilns are fired by burningcarbonaceous fuels such as gas,coal, coke and oil.

Bricks undergo a sequence offundamental changes as thetemperature builds up during thefiring process. The mostimportant of these are:

• Up to 150°CAny residual water from thedrying process is removed.

• 150°C–650°CClay minerals break down togive off water.

• 200°C–900°CBurn out of carbonaceousmaterial which may bepresent in the clay or addedas, for example, coke. Carboncan be important both in itscontribution to theappearance of a brick and asa fuel.

However, carbonremaining at the highesttemperature can contributeto bloating and it is vital to

control the rate oftemperature rise.

• 900°C–1250°CAt the highest temperaturesliquids form as a result ofpartial melting of componentsof the clay minerals. Oncooling the liquids form aglass which binds the brickinto a hard and durable unit.The characteristic coloursdevelop at this stage. In anormal kiln atmosphere themajority of clays will fire to ared colour but fireclays, forexample, yield buff/creamcoloured bricks. These basiccolours can be modified byadjusting the fuel: air ratio orby ensuring that some carbonis retained in the brick body upto the highest temperatures.

• CoolingAt 573°C silica, a majorcomponent of the body,undergoes a change involume. The rate oftemperature change throughthis zone is controlled,especially on cooling,otherwise internal crackingcan occur.

• ShrinkageIn addition to the shrinkagewhich takes place on drying,further shrinkage occursduring firing.

KilnsKilns can be divided broadly intotwo categories:• CONTINUOUS/SEMI-

CONTINUOUS Always insome part of the kiln bricksare being fired, unfired bricksare being introduced andfired bricks are beingwithdrawn. Continuous kilnsare more fuel-efficient than

intermittent kilns. Over 90%of UK clay bricks are fired inthis type of kiln.

• INTERMITTENT – the kiln isloaded with bricks which arethen fired, cooled, andremoved. The cycle is thenrepeated.

Intermittent kilns areused to achieve specificcharacteristics in theproducts or to fire smallquantities of bricks, forexample, special shapes.

INTERMITTENT KILNS(a) CLAMPSThe clamp method has a longhistory. It is still used today, to alimited extent, for firing stockbricks in S E England.

Essentially, a clamp is a largestack of closely set brickscontaining fuel. It is ignited atone end and left to burn. The firegradually proceeds along the fulllength of the clamp.

There may be over 1 millionbricks in a clamp. It is hand builtand situated outdoors, or with asimple roof cover. The wholestack is laid on a bed of fuel(usually coke) supported,typically, by a couple of coursesof bricks already fired. There issufficient fuel in the bricks (coke,old refuse, etc.) to raise thetemperature to over 1100°C.Some modern clamps are initiallyfired by gas instead of a bed ofcoke.

Firing is a lengthy process andthe whole cycle may take over6 weeks. On completion the bricksare withdrawn and sorted/packedon jigs raised into appropriatepositions.

Clamp firing produces a widerange of colours for a relativelylow initial capital cost.

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Once a clamp is ignited not agreat deal can be done to controlit. Some parts reach highertemperatures than others andsensitivity to climatic conditionsadds further variables. Yields offirst quality ‘best’ bricks can berelatively low.

(b) MOVING HOOD KILNSThe moving hood kiln is a recentdevelopment. It is findingincreasing use on small/mediumvolume stock brick plants as wellas for firing special bricks of alltypes.

The kiln runs via motorisedrollers on rails between two fixedhearths. At the completion of afiring the hood will move over thesecond hearth already loadedwith green, dried bricks (fig 6.96).Firing will commence immediately

and be completed in around3 days. The fired bricks from thefirst hearth are unloaded and thehearth filled with green driedbricks to await firing.

When used for stock bricks,energy for firing the bricks comesboth from the gas fired burnersin the kiln and the coke presentin the brick body. Each individualdense set stack of bricks behavesin a similar manner to a clampand is capable of yielding asimilar rich spectrum of colour.

(c) SHUTTLE KILNSSpecial shaped bricks are moredifficult to fire than standardbricks. It is often not possible tofire different sizes and shapestogether and special supportstructures are sometimesnecessary to ensure stabilityduring drying and firing. Specialbricks and small quantities ofstandard bricks are frequentlyfired in gas fired intermittentshuttle kilns. Products are set onkiln cars which are pushed intothe kilns, fired, cooled andwithdrawn for sorting andpacking.

ControlThe key changes which take placeas the temperature rises duringthe firing of clay bricks have beenlisted earlier. In conjunction withseveral other factors such as themineralogy of the clay mix andthe permeability of the body,these determine how rapidly abrick can be heated through eachtemperature zone. The faster thebricks can safely be heated thelower the fuel consumption.

A firing profile is compiled foreach body mix on a particularplant (fig 6.97).

Kiln

Hearth 1 Hearth 2

Figure 6.95. A burning clamp of bricks.

Figure 6.96. Principle of moving hoodkiln operation.

1200°C1000°C800°C600°C400°C200°C

0°C

Time from entry into kiln72 hours

Figure 6.97. A typical firing profile.

The objective is to control afiring in line with the targetprofile. Temperatures aredetermined by thermocouplessituated at strategic positions.When action is required inresponse to temperature datafrom thermocouples it may beeffected:

1. Manually2. Via a network of individual

electronic controllers3. Via a network of individual

electronic controllers managedby a computer (fig 6.98).

CONTINUOUS KILNSThere are two main types ofcontinuous kiln: a) tunnel kilnsand b) chamber kilns.

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(a) TUNNEL KILNS• Cars loaded with bricks move

through the fire. Around 55%of UK brick production is nowfired in tunnel kilns. The fuelused is, almost withoutexception, gas.

• Tunnel kilns first becamecommercially successfularound 1910. The basicconcept is illustrated infig 6.99.

• At intervals of, for example,75 minutes, a car of unfiredbricks is pushed into the kilnand a car of fired bricksemerges (fig 6.100). Thecars are pushed intermittentlyinto fixed positions andburners in the roof and/oron the sides, fire into thegaps or dykes between thecars. Typically there may be

40 cars in a kiln and the totaltime for each one to passthrough the kiln may bearound 2 1/2 days.

• The peak temperature andrate of heating and coolingmay be adjusted to suit anyparticular brick range.

(b) CHAMBER KILNS• The fire moves progressively

round the kiln. About 35%of UK brick production isfired in chamber kilns. Themajority of this volume is ofsemi-dry pressed Flettonsand coal is the predominantfuel.

• The prototypes of modernmoving fire, or annular,kilns were developed in the

mid-nineteenth century.The basic principle ofoperation is illustrated infig 6.101.

• The majority of kilns ofthis type are fed by coalthrough feed holes in theroof of each chamber.Much of the fuel forfiring Fletton bricks comesfrom carbonaceous materialwhich occurs naturally inthe clay.

• The operation is a continuouscircuit of setting, drawing andmoving forward of the firingzone from chamber tochamber.

• When the fired bricks are coolenough the next wicket willbe taken down, stacks of

Figure 6.98. Kiln control panel on amodern brick plant with computermanaged tunnel kiln firing.

Bricks

Burners

Kiln gases

900–1250°CBricks to be fired are set on a deck ofrefractory bricks. This is then seatedon an iron/steel base with two sets ofwheels

The car wheels run on rails. This partof the kiln is protected from the hotkiln gases by the deck refractoriesand seals on the sides

Figure 6.99. Outline of tunnel kiln operation.

Figure 6.100. Gas fired productemerging from a typical modern tunnelkiln.

Cool airFriedbrickscooling

Coal being fedin. Bricks beingfired at peaktemperatures

Bricksbeingdrawn

End ofprocess

Empty

Setting

Setting SetStart of process Hot gasesexhausted

Bricks awaitingfiring beingpreheated byhot gases fromfiring chamber(7, 8, 9)

Figure 6.101. Schematic diagram of chamber kiln operation.

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fired bricks will be withdrawn(fig 6.102) and, in due course,stacks of green bricks will beset.

Handling and packing of firedproductThe key objectives at this stage ofthe process are:

• To sort product into differentgrades and remove defectivebricks.

• Where necessary to blendbricks, especially multis toensure minimum variationfrom pack to pack.

• To minimise costs. Wherepacking is manual this canrepresent a significantcomponent of the totallabour costs of a factory.

Where unloading from kilncars and packing are fullymechanised (fig 6.103) systemsare still installed to allow allbricks to be individuallyinspected and defective bricksto be removed (fig 6.104).

Packs of bricks are oftensupplied wrapped inpolyethylene sheet to giveprotection from the weatherduring transport and storageon site.

CONCRETE BRICKS• Essentially concrete bricks

are composed of aggregates(e.g. crushed limestone,granite, etc.) bonded withcement and coloured withpigments (6.105).

• The bond is formed as a resultof a chemical reactionbetween the cement andwater. The strength of thisbond increases steadily withtime and continues after theproduct is built into place.

• The mix of aggregates,cement, water (and

pigment[s]/admixture[s] asrequired) is compacted intobricks by pressure, vibrationor high frequency hammeraction. In the UK the mostwidely used method isapplication of pressure usingmechanical or hydraulicpresses.

• The pigments used arepredominantly iron oxideswhich are totally durable andcolourfast.

• Brick presses operate continu-ously but mixing is carried outon a batch by batch basis.

Figure 6.102. Unloading stacks of firedbricks from a chamber kiln. The openwicket is behind the forklift truck.

Figure 6.103. Fully mechanisedunloading of fired stock bricks from akiln car.

Figure 6.104. Fired bricks aremechanically offloaded from a kiln caronto an inspection belt where defectivebricks are removed.

Cement Aggregate(s)

WaterPigment(s)

Admixture(s)

Mechanicalpress

Pack buildinggrabs

Aggregates account for 80–90% ofthe dry weight of concrete.

Portland cement is essentialbonding component. It is stored insilos where it is protected frommoisture

Curing

Finalpackaging/stockyard/despatch

Batchmixer

Figure 6.105. Typical plant layout formanufacture of concrete bricks.

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• Mechanical/hydraulic pressesare fed with semi-dryconcrete. The moisturecontent is in the range 4–7%and the water addition iscarefully controlled to ensurea product of consistentstrength and waterabsorption.

• The mechanical press infig 6.106 produces 8 bricksper cycle (about 4000bricks per hour). A rusticfinish is created by brushingthe stretcher faces whilstthe bricks are still in themould. Grabs buildgreen bricks directly intothe finished packconfiguration.

• Some concrete bricks havefrogs or perforations. But themajority of facing bricks aresolid and heavier than clayfacings.

• Smaller numbers of concretebricks are produced onmachines which compactprimarily by vibration.

• Size changes from pressed tocured bricks are negligible.Dimensional consistency istherefore a characteristic ofconcrete bricks.

• When pressed, concretebricks are weak butstrength increases steadilywith time. This process is

referred to as curing. Bricksare only released for salewhen they have reachedthe minimum strengthsspecified.

• Concrete facing bricks aregenerally shrink-wrapped andthe products also need to becovered on site.

CALCIUM SILICATE BRICKS• Calcium silicate bricks are also

referred to as ‘sandlime’ or‘flintlime’ bricks.

• Calcium silicate bricks arecomposed of aggregateswith a hydrated calciumsilicate bond and colourderived from pigmentadditions.

• The mix is moulded underhigh pressure in a mechanicalor a hydraulic press.

• The bond is formed asa result of a chemicalreaction between lime

and a siliceous aggregate.The reaction is promoted bycuring in autoclaves usingsteam at elevated pressuresand temperatures. Thisyields a strong, durableproduct.

• A typical plant layout isshown in fig 6.107.

• The aggregates account forabout 90% of the dry weightof the mix.

• Hydrated lime is stored insilos in powder form orgenerated on site byhydration of quicklime in areactor.

• The pigments used arepredominantly iron oxideswhich are totally durableand colourfast.

• Brick presses operatecontinuously but mixing iscarried out on a batch bybatch basis.

• The majority of calciumsilicate bricks are frogged and

Figure 6.106. Mechanical press forconcrete bricks.

Brickhandlingand despatch

Automatic pressand stacker withautomatic wagonchange

Aggregate weighhopper

Batchmixer

Water

Lime weighhopper

Colourpigment

PressTransfer car

Autoclave

Aggregate Lime

Figure 6.107. Typical plant layout for manufacture of calcium silicate bricks.

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BLOCKWORK INNER LEAVES, WALLS AND PARTITIONS 223

weights are comparable toclay bricks.

• Pressed ‘green’ bricks areloaded onto steel trolleys and

subjected to high-pressuresteam for 5–12 hours inautoclaves (fig 6.108). Afterpackaging the bricks areready for immediatedespatch.

• Size changes from pressedto cured bricks arenegligible. Dimensionalconsistency is therefore acharacteristic of calciumsilicate bricks.

• Property requirements andmethods of classification forcalcium silicate bricks arespecified in BS 187:1978. Fivestrength classes are listed from

20.5 N/mm2 to 48.5 N/mm2.Calcium silicate bricks whichmeet this standard are frostresistant.

• Calcium silicate brickshave negligible soluble saltcontents and are not,therefore, prone toefflorescence.

References(1) BS 5628-3:2001.(2) BS 4729:2005 ‘Recommendations

for dimensions of bricks (includingthose of special shape)’

(3) BS 5750-2 ‘Quality systems,specifications for manufactureand installation’.

Figure 6.108. Calcium silicate bricksemerging from an autoclave and ready fordespatch.

6.11 BLOCKWORK INNER LEAVES, WALLS AND PARTITIONS

This section deals withblockwork inner leaves andinternal walls and partitions.Building with facing-qualityblocks and common qualityblocks, fair-faced, is beyondthe scope of this section.

Types of blocksConcrete blocks are made inthree basic forms (fig 6.109).Solid blocks have no formedvoids, cellular blocks have one ormore which do not passright through the block andhollow blocks have one or morewhich do pass through the block.

Some manufacturers makeblocks with an insulant bondedto the outside of one face orinserted in the voids.

Typically, the nominal densitiesof blocks range between 475

and 2200 kg/m3. The leastdense, and usually lightest,being autoclaved aerated blocksand the most dense, and usually

heaviest, being solid densenatural aggregate blocks. Thereis a wide range of densitiesand weights between theseextremes.

Special shapes and sizesinclude cavity closers, quoin,lintel, fixing and coursing blocks.Some manufacturers makequarter, half and three-quarterlength blocks.

Handling, storage and protectionUnload blocks to a dry, levelsurface and protect fromexcessive wetting from theground and rain. Wet blocksshould be allowed to dry beforeuse to reduce drying shrinkagein the completed blockwork(see also Section 1.3 ‘Handling,storage and protection ofmaterials’).

Solid

Hollow

Cellular

Figure 6.109. Types of blocks.

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GeneralDo not mix different block typesin the same wall runs. Do not usebricks as closers as they willreduce the insulation value.

Setting outAs a trial, set out the first coursedry with 450 mm between thecentres of nominal 10 mm crossjoints. With so few joints there islittle scope for adjustments byvarying the joint widths, soconsider carefully the position ofcut blocks required at windowreveals (see ‘Bonding’, below).

Bedding and jointingUse only specified mortar mixeswhich will generally bedesignation M4 e.g. 1:1:6cement:lime:sand or 1:5masonry cement:sand.Designation M2 will usuallybe specified for autoclavedaerated blocks which have alow tensile strength and highshrinkage (see Section 4.1‘Mortars’). Solidly fill bed andcross joints. Do not deeplyfurrow bed joints (fig 6.110).

GaugeTake care to maintain gauge tocorrespond with brickworkgauge. Heavy blocks tend tosettle, causing ties to slope downto the inner leaf increasing therisk of water penetration.

Plumbing blocksBlockwork rises quicker thanbrickwork, causing fresh, soft,bed joints to be squeezed anddeformed. As a result blockwork,particularly the dense type, tendsto go out of plumb more readilythan brickwork.

Do not tap blocks sideways tobring them plumb as this tends

to open a gap on one side ofthe bed joint causing the blockto wobble. Rather than trying tofill this gap with mortar, plumbthe block by tapping down onthe high side and compact thejoint (fig 6.111). Heavier blocksmay need to be tapped toplumb and line with a clubhammer.

Aligning blocksBlocks should not be tappedsideways to bring the lower arrisinto alignment with the work

below. This may put the workbelow out of alignment. Instead,ease the block over the lastmillimetre or so by using just thetip of the trowel as a lever. Thetop arris is laid to the string line(fig 6.112).

• In general, cut blocks shouldbe not less than a half-blockexcept, for instance, in everyother course at reveals wherereturn or closer blocks may berequired (fig 6.113).

BondingAs blocks are available in manysizes and shapes it is notpracticable to illustrate allpossible bonding patterns. Whensetting out a bond pattern for aparticular job follow theprinciples described below.

• Lay blocks to a regular bondpattern, usually half-bond butunder no circumstances lessthan a quarter-block length(fig 6.114).

• Take care that broken bondis no less than quarter bond.If less and particularly if closeto a reveal, the vertical lineof potential weakness mayresult in shrinkage cracking(fig 6.115).

The result ofdeep furrowing

A solidbed joint

Tappingsideways opensbed joint

Tap down onblock to ‘moveover’ plumb andcompact bedjoint

Figure 6.110. Bedding concrete blocks.

Figure 6.111. Plumbing concrete blocks.

String linealigns topof block

Tip of trowelaligns blockwith coursebelow

Figure 6.112. Aligning a concrete block.

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• Corners may be bonded bycutting standard blocks orby using quoin blocks(fig 6.116).

• ‘T’-junctions are normallybonded (fig 6.117).Alternatively ties may beused with a straight joint(fig 6.118). Use butterflyties where verticaldifferential movementmay occur, e.g. wherean external leaf is builtoff a foundation and the

partition walls off asuspended floor.

Where vertical movementjoints are required to allowhorizontal movement, usesleeved debonding ties toallow movement but providelateral stability (see figs4.39a–c; Section 4.5 ‘Verticalmovement joints’).

Lintels• Set out bonding so that lintels

bear preferably on one wholeblock (fig 6.119). A minimumtwo-thirds length block isacceptable but not less(fig 6.120).

• Lintels should normally bearby at least 150 mm.

• Some types of hollow andcellular blocks may need tobe filled under lintel ends toprovide sufficient bearingstrength.

Support during constructionIn windy weather walls arereadily blown over if notrestrained by temporary proppingor by fixing floor or flat roofjoists. Alternatively the day worklift height may be reduced to suitcircumstances.

Hollow and cellular blocksThese can be cut satisfactorilyonly with a masonry bench saw(see Section 6.9 ‘Bricklaying toolsand equipment’). Cellular blocksare laid on a normal mortar bedwith the closed end uppermost.Hollow blocks are laid using ashell bedding technique by whichthe mortar is spread along theouter and inner bed surfaces only.

Movement jointsSince movement characteristicsbetween different types of

Cut blocks shownin light tone

Figure 6.113. Two examples of closingcavities at reveals to openings.

Normal half-bond

Quarter-bond

Minimum bond lap = ¼ block length

Figure 6.114. Normal and minimum bondpattern.


Figure 6.115. Badly placed broken bondcreating a vertical plane of weakness liableto cracking.

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Figure 6.116a. Purpose-made quoin return block.

Figure 6.116b. Quoinbonding with cut blockto form half-bond.

Figure 6.116c. Anacceptable alternative tofigure 6.116b.

Figure 6.117. ‘T’-junction – bonded.

Figure 6.118. ‘T’-junction – straightjoint and wall ties.


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concrete blocks vary widely,recommendations for the spacingof vertical movement joints maydiffer. But, in general, the spacingshould be no more than 6 m inaccordance with the MasonryCode of Practice(1) withoutconsulting the manufacturer.

Most manufacturers do notconsider movement jointsnecessary in the inner leaves ofhousing.

Reference(1) BS 5628-3:2001 ‘Code of practice

for use of masonry’.

KEY POINTS

■ Keep blocks dry before use.■ Apply full, solid cross joints.■ Maintain half-bond except where

unavoidable at reveals andcorners.

■ Use appropriate techniques toalign and plumb blocks.

■ Bed lintels on whole or two-thirdslength block.

■ Lintels should bear onwhole blocks by at least150 mm.

■ Maintain gauge to course withbrickwork.

Lintel bearing minimum 150 mm

Lintel bearing minimum 150 mm

Figure 6.119. Lintels should preferablybear on whole blocks.

Figure 6.120. Lintels should not bear oncut block.

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Brick is the oldest manufacturedbuilding material. The history ofits use gives many examples ofthe way techniques ofmanufacture and laying haveresponded to opportunitiescreated by different cultures, soinnovation has become a keyfeature in the development ofthe material. Today the industry isfaced with a number ofchallenges which requireinnovative approaches if they areto be met successfully.

The importance of conservingnatural resources and therecognition that by burning fossilfuels we are damaging theenvironment have led to aninterest in sustainability, that isthe responsible use of resourcesbe they human, physical orfinancial. Brick manufacture hasalways been an energy-intensive

process so the industry hasbegun to experiment withproduction techniques that useless energy or take advantage ofalternative forms of energy. Thusthe addition of glass cullet to theunfired clay has been found toreduce the firing temperature inthe kiln by up to 100°C and kilnshave been fired by methane gasextracted from landfill sitesformed in exhausted clay pits.

However, the strongestarguments for the sustainabilityof bricks and brickwork are to befound when the product is inuse. It is sustainable to use anestablished product, laid by anexperienced workforce, especiallywhen it results in a building thatis attractive and has a long lifewith low maintenance.

Whilst the growth of interestin sustainability obliged

manufacturers to review themanufacturing process, thedemands of the constructionindustry have forced them toreconsider the products. Sir JohnEgan chaired the ‘ConstructionTask Force’ with the remit ofidentifying areas requiringsignificant improvement in theindustry. It is anticipated that hisideas will reduce capital cost andconstruction time, with greaterpredictability of performance andfewer defects. The reduced riskof accidents and betterproductivity will lead to increasedturnover and profit.

The brick manufacturer’sresponse to the challenge hasbeen to produce innovativesolutions across a range ofproducts from the individual unitto complete constructionsystems.

7 INNOVATION

7.1 THE INDIVIDUAL UNIT1

The traditional brick used inconjunction with a range ofspecials is able to producebrickwork that has variety incharacter, however somemanufacturers have developedsingle units that satisfyparticular requirements.

UNIVERSAL JOINT – OR ‘EASYANGLE’

A single unit that can createpractically any angle in brickworkboth internal and external (fig 7.1).

Available in smooth red, smoothblue and sanded red stock, thebrick compliments any main bricktype to provide an attractivesolution to the corner (fig 7.2).

Figure 7.1. Easy angle brick. Figure 7.2. Easy angle brick – in use.

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THE INDIVIDUAL UNIT1 229

TILE BRICKAn innovative alternative to thetraditional ‘tile-hung’ finish(figs 7.3, 7.4). Tile hangingrequires a contractor to employa number of trades to engage ina sequence of operations. Oncethe backing wall is complete ithas to be weatherproofedbefore the tiling battens areinstalled and the tiles fixed. Thetile brick allows the bricklayersto continue bringing up the wallwhilst producing a decorativefinish akin to tile hanging. Thetile brick is a robust unit withlower maintenance and less

likelihood of damage than tilehanging.

NEW FORMATSBrickmakers have alwaysmanufactured a range of sizesbut recently some haveintroduced ‘large format bricks’.These clay units compete

158 mm

102.5 mm

168 mm

Figure 7.3. Tile brick.

directly with claddings thatrequire secondary fixingsystems. Units are manufacturedin sizes of 440 � 215 � 100and 327 � 215 � 90 andincorporate traditional mortar.The units are extremely durableand the structural properties ofwalls built in the format areexcellent. The blocks aredimensioned to allow them tobe incorporated into atraditional cavity wall tied backto the inner leaf (figs 7.5, 7.6).

Figure 7.4. Tile brick – in use.

Figure 7.5. Fireborn – large format clayblock.

Figure 7.6. Fireborn – in use.

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230 INNOVATION

The Egan Agenda requiresspeed of construction andlack of defects. One way toachieve this is to design andmanufacture componentsthat can be incorporatedinto brickwork on site,thereby enabling details tobe created quickly andeasily without extensivecraft skills.

BRICK LOAD-BEARINGOR NON-LOAD-BEARING FLAT

ARCH/SEGMENTAL ARCHBrick slips are permanentlybonded to a masonrysubstrate that also acts as theload-bearing lintel. Units arefactory-built, prefabricatedmodules that are post-pointedto create a match with existingbrickwork (fig 7.7).Other prefabricated load-bearing arches are based onsteel lintels. Brick slips areattached to a plate incorporatedin the lintel. The lintel ispositioned over the opening andthe surrounding brickwork islaid to it (fig 7.8).

BRICK BONDING COURSES –SOLDIER, POLYCHROMATIC

AND DENTILPre-assembled brickworkmodules that can be cut onsite with returns available forcorners. The units areincorporated as thebrickwork proceeds and arethen post-pointed to create amatch (figs 7.9, 7.10, 7.11, 7.12).

7.2 INNOVATION IN COMPONENTS

Figure 7.7. Load-bearing brick arch.

Figure 7.8. Steel lintel with brick arch insert.

Figure 7.9. Soldier course in brickwork.

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INNOVATION IN COMPONENTS 231

Figure 7.10. Dentil course.

Figure 7.11. Stack bond soldier course.

BRICK PANELS: STACKBOND, QUOIN AND BASKET

WEAVEPre-assembled brickworkmodules formed by permanentlybonding slips to a lightweightmasonry substrate.Decorative infill panelsmade from thin compositepanels comprising of backingmaterial with a brick slipfinish allow complex bondsand patterns to be achieved.The panels are lightweightand easily transportable.They are fixed mechanicallyon site (figs 7.13, 7.14).

Figure 7.12. Stack bond stretcher course.

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232 INNOVATION

Figure 7.13. Coin pieces.

Figure 7.14. Herringbone brickwork on a lightweight panel.

7.3 INNOVATION IN PREFABRICATION SYSTEMS

The Egan Agenda proposesthat, wherever possible,buildings should beconstructed from prefabricatedcomponents therebyreducing the amount of workrequired on site. Thereforebrick manufacturers havebeen obliged to design andproduce systems suitable forprefabrication.

The systems use a variety offormats extending from bricksto brick slips to speciallydesigned clay units.

BRICK SLIP SYSTEMSWonderwall is a composite panelsystem that comprises a clay brickslip finish attached to the backingpanel/carrier sheet, which in turn isadhered to a Styrofoam insulation(figs 7.15, 7.16, 7.17, 7.18).

The carrier sheet allows fordimensional deviation which isalways present with clay bricks.

Figure 7.15. Wonderwall – fixing thecarrier sheet.

Figure 7.16. Wonderwall – applying theadhesive.

Figure 7.17. Wonderwall – applying themortar.

Figure 7.18. Wonderwall – finishing thejoint.

The setting out process duringconstruction will accommodatesize variation within the mortarjoint. Slip thickness may varybetween 25 and 35 mm

thereby allowing for specialfeature details to beincorporated into the finishedpanels such as corbels, stringcourses and quoin details. Special

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INNOVATION IN PREFABRICATION SYSTEMS 233

pistol brick slips enable continuityaround the corners of buildingsand at head, jamb and sillpositions.

The wall panel is completed bypointing the joints with apurpose-made pointing mortaravailable in various colours.Although the system commonlyuses standard 65-mm high brickslips there is no limitation onthe unit lengths, which include290-mm long clay products.

The adhesive used for fixingbrick slips onto the backing panelhas a flexible composition thatallows for differential materialmovement and brick slipexpansion. Vigorous cyclicfreeze–thaw tests have ensuredthat the frost resistant clay slipsand carrier sheet combinationwill endure severe weatherconditions.

PermaFast is a factory-builtpre-assembled system thatcomprises a lightweightgalvanised steel framework ontowhich is fixed a combination ofsheathing board and profiledcementitious backing board witha facing of clay brick slips, givingthe appearance of conventionalbrickwork.

The boards are mechanicallyfixed to the steel frame and brickslips are bonded to thecementitious board with anadhesive. The joints are pointedand sealed with a cementitiousmortar.

Panels are available in varioussizes, up to a maximum of 6 m �3.6 m. The depth of the panel istypically 150 mm, depending onthe loading and spans. Thepanels are designed to beinstalled onto steel or concreteframes of new, or existing,buildings. Panels incorporate

openings as required withpre-formed DPCs. If specified,windows and doors can befactory fitted withfinished external reveal detail.

BRICK TILE SYSTEMSCorium is a system that makesuse of uniquely profiled brick tilesfixed mechanically to agalvanised steel backing section(below DPC, stainless steel isused). Corium can be supplied asa prefabricated panel, deliveredfully mortared or, as a site-basedsystem, installed by approvedinstallers (figs 7.19, 7.20, 7.21).

Rows of profiled steel sectionsare fixed to the backing structure.The sections are designed tointerlock vertically. The brick tilesare then clipped into place using arubber mallet. The clippingprocess ensures that consistenthorizontal joints are achieved,whilst vertical joint spacing can beadjusted to suit designrequirements. Once tiles areinstalled they are pointed with a1:1:6 cement:lime:sand mix whichis applied using a pump system.

The basic range of brick tilesis produced in a face size of

215 � 65 mm supported by arange of standard specials thatinclude external return,stop-end, plinth, sill, dado andsoldier bricks. It is possible toproduce brick tile in a 290 �215 mm face size which givesdesigners the possibility to mixand match tiles on a facade.

PREFABRICATED BRICKWORKThere are now numerous examplesof brickwork being laid in a factoryand then transported to site. Thetwo-storey columns at the InlandRevenue building in Nottinghamare a good example of thistechnique. The brick needs to be

Figure 7.19. Corium – fixing the backingsheet.

Figure 7.20. Corium – fixing the tiles.

Figure 7.21. Corium – applying themortar.

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THIN-JOINT GLUEDBLOCKWORK AND BRICKWORKThe use of thin-joint mortar iswell established inContinental Europe and thetechnique has recently beenintroduced into the UnitedKingdom for both block andbrickwork.

Thin-joint glued mortar iscement-based and it is supplied

234 INNOVATION

Figure 7.22.Prefabrication ofcolumns.

7.4 INNOVATION IN TECHNIQUE

as a dry, pre-mixed powderthat is easily prepared on siteby adding the appropriatequantity of water. It is appliedwith a proprietary scoop orsledge which creates a consistentjoint thickness of only 3 mm.The mortar starts to set within10 minutes and approachesdesign bond strength in just1–2 hours (figs 7.23, 7.24).

The increase in bond strengthand the speed and accuracy ofjointing lead to significantsavings in build time. The quickbond time means that themasonry does not squeeze outwet mortar in the lower courses,thus enabling greater wallheights to be built in a day. Thestrength of the bond allows theinstallation of floors and roof

post-tensioned to allow it to bemoved, but this can also contributeto the load bearing qualities onceit is positioned on site (fig 7.22).

Another example ofprefabrication is the spandrelpanel used at the Powergenbuilding in Coventry. Here, theextruded bricks were stackbonded and the panel wastensioned by passing steel barsthrough the voids in the extrudedbrick, thereby allowing the wholepanel to be moved from thefactory to the site.

The thin-joint glued brickworksystem has been used inprefabricated panels. The keybenefits of the system arestrength, durability and improvedquality. But it is the strength ofthe system that makes such anattractive proposition forprefabrication, because it ispossible to build a single skinpanel of brickwork possessingsufficient strength to allow fortransportation and lifting intoposition. Details of the system areexamined below.

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INNOVATION IN TECHNIQUE 235

Figure 7.23. Thin-joint brickwork – applying the mortar.

timbers the following daythereby allowing other tradesto start sooner.

Where external walls are ofcavity construction the innerleaf can be built first, enablingeasier inspection of blockand easier fixing of anyadditional insulation, thusimproving quality. The accuracyof thin-joint constructionmeans that additional finishessuch as spray plaster canbe applied directly to theblockwork, speeding up theoverall build process. It isgenerally accepted that thin-joint masonry leads to cleanersites, considerably less wastageof blocks and mortar, andimproved air-tightness of theconstruction.

Thin-joint mortars can alsobe used for brickwork. As withblockwork this is a techniquethat has been introduced fromContinental Europe. It relies ona similar mortar which is mixedand laid using a proprietarymachine. The machine mixes themortar and dispenses it via atwo-part gun nozzle. The pumpis generally placed on thescaffold which can result inslightly wider scaffolds in orderto maintain access. The lengthof the pipe from the gun to themachine is typically 8 m giving aworking span of approximately15 m. The bed joints can becontinuously mortared with thegun and the perpends aremortared by aligning the brickson their ends in rows andcontinuously mortaring prior toplacing. Once the mortar ismixed it quickly starts to curethereby allowing bricklayersto lay more courses per day. Figure 7.24. Thin-joint brickwork – in situ.

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236 INNOVATION

FRAMESBuild in frames as work proceedsor use a template to give plus10 mm both vertically andhorizontally.

MOVEMENT JOINTSMovement joints should beprovided at the same frequencyas in traditional brickwork.

LINTELSTraditional lintels can beused for thin-jointbrickwork. In Belgium workhas been undertakenwhereby lintels are omittedaltogether; the thin-jointbrickwork being reinforcedby bed-joint reinforcement inthe three courses over theopening.

WALL TIESDue to the offset horizontalbonding that may occur owingto the thin external joints,some thought needs to begiven to the suitability of wallties in brick and blockconstruction. Ties similar tothe ‘fast-track short channelstrip’ were found to beadaptable for use regardless ofthe size of the block used toform the inner leaf.

The fast-track channel isbuilt into the inner leaf ofblockwork ready to take a tiefrom the outer leaf. Thismethod of construction avoidsthe dangers of projecting tiesand has proved to be verysatisfactory.

Figure 7.25. Thin joint brickwork –textured surface.

• The use of thin-jointbrickwork gives talenteddesigners the opportunityto be innovative in theiruse of bricks because it ispossible to mix sizes andbonding patterns, creatingoriginal and exciting clayfacades.

The detailing of thin-jointbrickwork generally followsconventional practice.

DIMENSIONSThin-joint masonry in Eurocode6 is defined as having amaximum joint width of3 mm. However, this can bedifficult to achieve in practiceand a mortar width of 4 mm isoften used. Any size of brickcan be used in thin-jointbrickwork and the brickworkshould be set out to the brickplus 3 mm.

DPCS AND WEEPHOLESDPCs are laid as in traditionalconstruction, the materialbeing sandwiched betweentwo layers of thin-joint mortar.Weepholes should be providedat 1.2 centres by omittingperpends.

JOINTINGMortar is laid at least 10 mmback from the external face ofthe brick. Care is needed toavoid mortar disfiguringthe brickwork face. It isdifficult to remove withoutleaving stains.

In order to prevent the gun fromblocking, continuous operationis required. The machine needsto be thoroughly cleaned at theend of each day, preferably witha power washer.

Thin-joint brickwork raisessome interesting architecturalissues:

• The absence of pointing inthin-joint brickwork meansthat the appearance of thefinished wall is unlike that ofconventional brickwork. Thecolour and texture of thebrick is enhanced because it isnot moderated by the mortarjoint.

• Thin-joint brickwork makes iteasy to manipulate brickswhen the wall is being built. Itis therefore possible tointroduce surfacemodelling by laying bricksat different angles oraltering the plane of thework by recessing andadvancing the face of thebrickwork (fig 7.25).

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INNOVATION IN CONSTRUCTION SYSTEMS 237

7.5 INNOVATION IN CONSTRUCTION SYSTEMS

SINGLE LEAF MASONRYSingle Leaf Masonry has beenused in both the United Statesand Europe but it was notuntil the 1980s that researchwork was carried out in theUK by CERAM (CeramResearch Limited).

The aim was to investigateways in which single leafinsulated masonry could beused effectively and safely toform a structural shell of asingle-or two-storey house.The first Design Guide forsingle leaf masonry usedstandard format UK bricks and,although houses were builtusing the system, the wallsrequired propping duringconstruction and the connectionbetween the masonry skin andthe first floor was difficult toachieve.

Recent development of thesystem has been carried out byCERAM as a Partner inInnovation programme forthe DTI with further supportfrom NHBC, BDA and BRCSpecial Products. This hasresulted in a further DesignGuide and the construction of ademonstration house in Burtonon Trent (figs 7.26, 7.27, 7.28).

The key developments inthis project are theintroduction of a larger andwider clay unit (290 mm �140 mm � 65 mm, L � W � H)leading to enhanced stabilityduring construction,improved thermal insulation,proven acoustic performance

and a redesigned floor-to-wall connection. TheDemonstration Housematches the thin structural wallto a pile and ground-beamfoundation system. Overallthe construction meets allregulatory requirements, isstrong on economic andenvironmental grounds and usesskills efficiently.

The single-skin masonryis lined internally with awaterproof insulant to whichis fixed the internal finish. It isa development of traditionalbuilding techniques thatenables advantage to be takenof the wide range of colourand texture provided by claybrick masonry when used inconjunction with high gradeinsulating material. TraditionalPlus is a method of buildingwhich makes the mosteconomical use ofmaterials and is based oncarefully calculated designs.It complies with therelevant Codes of Practice aslong as it is built inaccordance with the designdetails.

Figure 7.28. Traditional Plus – floor-to-wall detail.

Figure 7.27. Traditional Plus – corner.

Figure 7.26. Traditional Plus – brick andlintel.

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INDEX

Absorbency (of bricks) xv, 4, 5, 32,35, 36, 81

Actual size xi, xii, xv, xvi, 12, 13, 14,16, 17, 25, 181, 183, 214

Admixtures for mortar xiv, 34, 51,81, 172

Air entraining additive xi, xiv, 39, 51Ancillary and accessory components

9, 23, 211Angle bricks xii, 45–6, 49Angle grinder xi, 122, 211, 212Angle support xi, 65, 109, 135Anti-freeze for mortar 51, 52, 82Appearance vii, xii, xiii, xv, 3, 12,

14, 17, 21, 28, 37, 58, 112,124, 129, 143, 186, 213

Arch brick sets 45, 127, 128Arch xi, xiii, xv, 125–7, 132, 230Arches, curved v, xi, 124, 129, 161Arches, soldier v, 38, 133, 134,

137, 161Arris xi, 26, 30, 47, 118, 146,

151, 208ATR’s xi, 184Autoclave xi, 53, 93, 222–4Axed arch xi, 125

Band course xi, 16, 136, 184Base slabs 70Basket weave bond xi, xii, 140, 141Bat xi, 28, 32Batching (mortar) xi, 43, 59, 80,

172, 173Bed face xi, 66, 103Bed joint reinforcement 99, 101Bed joint xi, 33, 41–2, 71Bed xi, 23, 65, 114, 127Bench saw xi, 33, 211Benching xi, 71Bevel (Bevel square) xi, 141, 152Blending facing bricks v, 53Blockwork v, xi, xiii, 59, 233, 234Bolster xi, 209Bond xi, xv, 45, 63, 138, 224Bonding bricks xi, 224Boulder clay xi, 215Bracket supports 64, 106, 108Brick Development Association (BDA)

iv, ix, 68, 73, 107, 118, 144

Brick dimensions 12Brick gauge xi, 29, 31Brick slip systems 232–3Brick tile systems 233Brick xi, 7, 15, 26, 122, 212Brickearth xi, 215British Standards, for bricks vii, xi,

xiii, 44, 182Broken bond xi, xv, 29, 188Bullnose xi, xv, 44, 46Bulls-eye opening xi, 129

C&GIL (see City and Guilds Instituteof London)

Calcium silicate brick xi, 52, 53,122, 171

Cant bricks xi, xv, 46–7, 67Capping xi, 63, 112, 123, 179, 184Care of tools 210, 212Cavity batten xi, 103Cavity insulation (see Insulation in

cavity walls)Cavity tray (see DPC tray)Cavity wall ties xvi, 62, 111, 204Cavity wall ties, spacing xii, 111,

204Cavity walls v, xii, 56, 64, 82, 87,

89, 191, 195Cellular block xii, 60, 225Cement xii, 8, 11, 50, 77, 169,

175, 177Centring 125Chases, in blockwork xii, 59, 60Chimney breasts v, 155Chimney stacks v, 161, 162, 167Chimney terminals 157, 161Chimney, height of 162Cill (see Sill)Circular opening xi, 129Circular work 101CITB (see Construction Industry

Training Board)City and Guilds Institute of

London viii, xiiClamp xii, 218Clay brick xii, 52, 123, 175,

184, 214Clean work v, 33Closers xii, 45, 62, 72

Club hammer xii, 209Co-ordinating size xii, 12Coarse stuff (see also Ready-mixed

lime/sand) 9, 80Cold weather working 37, 52, 86Collar joint xiiColour banding xi, xiv, 55Colour variation 2, 43, 56, 186Coloured mortar 135Common brick xii, 214Compressive strength xii, 67,

176, 213Concrete blocks xii, 57, 223Concrete brick xii, 221Concrete xii, 113, 213Construction Industry Training

Board vii, xiiConstructional hearth xv, 157Coping v, xii, 112Corbel support system 111Corbel xii, 111Corbelling v, 147–51Corners block 25, 208Corners xi, xiv, 21Course xii, 86, 110, 136, 142, 150,

151, 230Cross joint xii, 33, 41Curved work xvi, 45, 143Cutting bricks v, xi, 31, 125Cutting pack bands 8

Damp proof courses (see DPC)Datum xii, 18, 21, 25, 72,Decorative brickwork v, 135–43, 162Definitions viii, 1, 44, 112, 157, 168Dentil courses 230Detergent 78, 169Diaper work xii, 136Distribution on site 7Dog toothing 141Dogleg bricks xii, 45Door frame xv, 62DPC brick xii, 117, 213DPC cavity trays xii, 87DPC tray xii, 119, 164DPC xii, 236DPC’s vertical 63, 87DPM xii, 157, 170, 204Drainage xii, 74, 180

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240 INDEX

Drawings 197, 206Durability v, 176

Eaves xiiEfflorescence xii, 168–70Elevation xii, 96Engineering bricks xii, 70, 214Estimating quantities v, 10Exposure to wind driven rain 164,

174, 191External walls (see Cavity walls)Extrados xii, 130Extruded wire-cut bricks xii, 56, 217

Face work xiii, 161, 214Facing brick v, xiii, 53, 57–8, 222Fireclay xiii, 218Fireplace openings v, 155, 156,

157, 158, 160Flashing xiii, 121, 122, 195Fletton bricks xiii, 217, 220Flexible DPC’s 2, 86, 109, 116Flintlime brick (see also Calcium

silicate brick) xiii, 171, 181, 222Flues v, 155, 160, 161, 162Footing xiii, 22, 33, 71Foundation xiii, 11, 20, 21, 24, 86,

102–3, 104, 144, 157, 204,225, 237

Frames 236Frenchman xiii, 41, 42Frog 4, 8, 10, 11, 45, 66, 117, 142,

216, 217, 222Frog, up/down v, 10, 11, 32, 48,

66–9, 73, 150, 190Frogged bricks 31–2, 66, 69, 150Frost attack v, 51–2, 59, 112, 152,

171–3, 176, 196, 213Frost damage xiii, 50, 62, 171Frost resistance v, 51, 171–3, 175,

176, 213Frost, protection from 5, 50, 51–2,

81, 171, 172, 176, 213Full-fill insulation (see Cavity insulation)

Gable xiii, 85, 90, 92–3, 114–15,154, 199, 211

Gauge boxes xiii, 80, 188Gauge for brick cutting v, xi, xii,

31–3, 34, 41–2, 49, 122, 131,139, 183, 207, 209–10, 211–12

Gauge rods xiii, 17, 58Gauge, brickwork xi, 128, 134,

139, 224Gauged arches xiii, 125

Gauging down 20, 24, 72Gauging mortar 43, 114Gault clay xiii, 215Glossary of terms xi–xvi, 157Grouted cavity reinforced brickwork

99, 102Gun template xiii, 126, 152, 153

Hammers 31, 209, 210Hand-made bricks 182, 190Handing (LH or RH?) 47–8Handling and storage 6, 7, 8,

58, 223Hatching and grinning xiii, 189–90Hawk xiii, 40Header xiii, 44, 46, 59, 74, 128,

137, 142–5, 148, 150, 189, 192Herringbone bond 137, 138, 139,

140, 141Hod xiii, 56Hollow block xiii, 223, 225Hot weather 207, 208

Increment xiii, 16, 17Inspection chambers (see also

Manhole) 69, 180, 181Insulation batt xiii, 9, 83,

186, 204Insulation board xiii, 84, 92, 196Insulation in cavity walls 56–9, 62,

64, 89, 92, 93, 120, 191, 192Insulation material xiii, 58Insulation, injected and blown 55,

60, 78, 93, 187, 225Interlacing bond 141Intrados xiii, 126, 130Invert arch 130–2Invert xiii, 130, 131Isometric xiii, 158, 199, 201,

202, 203

Joint profile (see also Mortar joints)xiii, 2, 40, 190, 194

Jointer xiii, 37, 38, 39, 114, 118,190, 207

Jointing xiii, 236

Key brick xiii, 126–8, 130, 131–2, 214

Kiln xiii, 53, 54, 55, 183, 217, 218,219, 220, 221, 228

Lateral load xiii, 69, 98, 100, 105Leaf xiii, 91, 92, 103, 110, 121,

126, 142, 237

Level xiii, 20, 23, 29, 72, 91, 93,149, 175, 188, 208

Lime (hydrated) xiv, 3, 11, 77, 80,170, 222

Lime (hydraulic) xiv, 76, 77Lime in mortar xii, xiii, 35, 52Lime putty xiv, 125, 128Lime stain (bleed or bloom) xiv,

106, 168, 170Lime/sand mix (see Ready mixed

lime/sand)Limits of size, brick xvi, 183, 184Line block (see Corners block)Line, lining-in 20, 22, 25, 26, 28,

47, 113, 115, 116, 130, 208Lines and pins 208Lintel xiv, 236Lintels 236Load-bearing brick arch 230Loading out 8, 54, 55, 72, 183,

186, 187Loading out on suspended

floors 225

Manhole xiv, 50, 69, 71, 72, 74,180, 181

Manufacture of bricks 168, 169,171, 175, 183, 184, 186, 195,196, 212, 228

Manufacture, calcium silicate bricksxi, 43, 52, 53, 94, 97, 123, 171,173, 175, 213, 222, 223

Manufacture, clay bricks xv, 51,52, 53, 54, 64, 71, 94, 95, 97,106, 123, 152, 168, 171, 174,175, 176, 182, 184, 196, 214,217, 218, 219, 223, 232, 233, 237

Manufacture, concrete bricks 53,221, 222

Marl xiv, 214, 215Masonry cement xiv, 77, 79, 81,

172, 177, 224Mechanical damage, protection

from 5, 59Metal support fittings 64, 65, 76,

106Mixing mortar 11, 59Mortar joints 36, 61, 123, 186, 194Mortar mixes 43, 78Mortar xiv, 10, 35, 58, 76, 123,

169, 174, 236Movement joints 64, 65, 94, 97,

123, 190, 225, 236Murals 135, 142

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INDEX 241

OPC (see Portland cement, ordinary (OPC))

Packs of bricks xiv, 7, 55, 183, 221Parapet wall xiv, 62, 119Partial-fill insulation (see Insulation

board)Partition wall xiv, 225Patterned brickwork (see Decorative

brickwork)Perforated bricks xiv, 32, 129,

150, 152Perpends (perps) xiv, 13, 27, 28Perpends, verticality of xiv, 13Pier xiv, 23, 27, 185Pigments xiv, 78Pins, line xiv, 143, 208Pistol brick xiv, 135, 233Plan xiv, 46, 70, 74, 142, 160, 163,

197, 201, 202, 203Plant and people, protection

from 5Plasticiser xiv, 39, 76, 78, 81,

169, 172Plinth xiv, 45Plugging chisel xiv, 8, 131,

209, 210Plumb level xiv, 2, 149, 208Plumb xiv, 145, 208, 224Pocket reinforced brickwork 104Pointing xiv, 36, 38, 40, 42, 43, 62,

136, 190, 207Polychromatic brickwork xiv, 135Polychromatic courses 230Portland cement, ordinary

(OPC) xiv, 76, 77, 79, 160,169, 170, 173, 177, 187, 221

Post tensioned brickwork xiv, 101, 105

Prefabricated brickwork 233–4Preparation v, 50Pressed bricks xiv, 223Profile boards xiv, 96, 210Profiles xiv, 96, 210Protection v, 7, 52, 187

Quality Control of bricks188, 214

Quantities 10Quetta bond 100, 104Quoin block 20, 226Quoin xv, 20, 21, 226, 231

Racking back xv, 30Radial bricks 145

Rain 81, 190, 193Rain resistance 33, 36, 56, 61,

129, 213Reading drawings 197Ready mixed lime/sand 9, 43, 51,

78, 80, 81, 136Reference panel xv, 2, 186Reinforced brickwork xv, 105Render xv, 119, 178, 179, 181Repointing xv, 36, 38, 40, 62, 127,

190, 208, 211Retaining wall xv, 105, 112, 172,

174, 175, 180, 181Retarded ready-to-use mortar 34,

51, 58, 78, 79, 81, 98, 187Returns xv, 45, 48, 149, 230Reveal xv, 13–16, 29, 42, 59,

133, 188Reverse bond xv, 14, 15, 58, 188Rigid DPC’s 86Rough arch xv, 125

Safety 32, 212Salts (see Soluble salts)Sample panel xv, 1, 3Sand xv, 9, 35, 77Sandlime brick (see also Calcium

silicate brick) xv, 53, 94, 171,181, 222

Saw (see also Bench saw) 32, 211Scaffolding xv, 5, 7, 36, 51, 52, 55,

169, 211Scale of drawings 198,

200, 206Scutch xv, 32, 125, 209, 210Sealant xv, 9, 39, 64, 65, 95, 96,

98, 107, 109, 122, 190Section xv, 56, 71, 74, 102,

104, 106, 148, 151, 158, 163,165, 233

Segmental arch 125, 126, 127,128, 230

Semi-dry pressed bricks xv, 66, 216,217, 220

Setting-out brickwork 12Setting-out facework 12, 29, 54,

183, 188Shale xv, 214, 215Sill xv, 5, 18, 24, 38, 57, 59, 63,

64, 86, 88, 169, 172, 174, 175,176, 178, 179, 181, 183, 184,185, 195, 233

Single leaf masonry 237Size variation, brick 53, 181, 182,

183, 214

Size, brick xi, 7, 10, 13, 14, 17, 31,32, 43, 44, 67, 125, 126,

Skewback xv, 125, 126Slate DPC’s 86Sliding restraint ties 111Soft-mud bricks xv, 56, 184Soldier arches 38, 124, 133Soldier bricks 110, 136, 137, 233Soldier courses 136, 184, 230Solid blocks 223Soluble salts 168, 175, 213Sound insulation 68Spacing wall ties (see Cavity wall ties,

spacing)Special sizes 7, 44, 214, 223Specials (Special shaped bricks) 2,

44, 45, 112, 219Spirit level xv, 21–3, 30, 141, 142,

145, 208, 210Spot board xv, 8, 32, 35, 72, 136Springing xv, 18, 125, 126, 127Squint xv, 45, 46, 47, 183SRPC (see Sulfate resisting Portland

cement (SRPC))Stack bond 231Stock bricks xv, 26, 184, 189, 216,

218, 219, 221Stop (bricks) xv, 48Stop end (bricks) xv, 48Stop ends (for cavity trays)

57, 195Storage 6, 7, 44, 186Storey rod xv, 16, 18Stretcher bond 136, 144Stretcher xv, 12Strip foundation xv, 24, 144Suction rate xv, 35, 36, 37, 52Sulfate attack xv, 43, 59, 71, 112,

119, 123, 172, 173, 174, 175,176, 196

Sulfate resisting Portland cement(SRPC) 79, 177

Sulfates in bricks 71Sun and wind, protection from 5,

123Support systems 64, 106, 107Symbols on drawings 205

Tailing-down 150, 151Template xvi, 125, 126, 127, 129,

132, 139, 141, 142, 143, 144,145, 146, 148, 149, 150, 152,153, 236

Terminal, flue 157, 161, 162, 163, 164

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242 INDEX

Textured bricks 29, 36, 47, 67Thermometer 50, 51Thin bricks 17, 236Thin-joint brickwork 234–6Throat (coping/sills) 59, 169, 172,

174, 175, 176, 179, 183Throat (flue) xvi, 157Ties (see also Cavity wall ties) xvi,

62, 82, 83, 93, 97, 111, 194, 236

Ties for movements joint 97Tile brick 229Tingle plate xvi, 26, 28, 116Tolerance xvi, 2, 53, 54, 57, 102,

107, 108, 136, 182Tools and equipment 207Toothed quoin 72, 73Training 68

Trammel xvi, 144Trowel xvi, 31, 33, 36, 207Tuck pointing xvi, 38Tudor bricks 17Tumbling-in 151

Unit of Competence xvi, 229

Variation in size 53, 181, 182, 183,214

Verge xvi, 169, 175Vertical DPC’s 57, 63, 64, 87, 88,

192, 195Voussoirs 124, 125, 127, 128, 129,

130, 131, 132

Wall joint xvi, 64Wall tie, two-part xvi, 63, 148

Wall ties xvi, 82, 111, 194, 236Wall tiles 236Walls 70–1Washing-up liquid (see Detergent)Wastage 11, 44, 49, 56, 152, 235Water absorption xvi, 37, 52, 171,

176, 213, 215, 222Water for mortar 4, 35Waterproof finishes 196Weather forecast 52Weephole 236Wind, protection from 5, 9, 51,

78, 98Winter working 37, 38, 40,

50, 214Work size 12, 17, 32Working-in components 18, 19,

50, 73

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BDA Guide to Successful Brickwork, Third Edition