Concrete Block Walling

Block Walling: Advantages

Versatile, durable and strong

Fire resistant

Excellent sound insulation

Ideal background for dry lining wet

finishes and fixings

Inherent thermal mass acts as heat

store

Recyclable

Proven building method and

longevity

Widely and readily available

Cost effective

Block Walling: Standard Dimensions

The standard size of a concrete block is 440mm x 100mm x 215mm.

Block Walling: Nominal Weights

The weight of a concrete block is dependant upon the type of block (e.g. solid, hollow, cellular, special), the classification of the block (e.g. dense, lightweight, super-lightweight) and the

manufacturer. The table above shows examples of block weights. It is recommended that you consult the product data sheet to establish the weight of a specific block.

Description of Block Weight of Block

Solid dense block (standard) 18.5kg

Solid lightweight block 13.2kg

Hollow dense block 18.7kg

Block Walling – Terminology

Back

Face

Joint

Joint

Top bed

Bottom bed

Block Walling: Comparable Dimensions

A standard sized concrete block has the equivalent surface area of six bricks. This is purposely designed to enable blocks and bricks to be built together with minimal need for cutting material.

Block Walling: Block Classifications

There are various classifications of concrete block. Each type of block is designed for a specific purpose. Care must be taken to ensure that you specify and/or order the correct block for each

job. The next two slides show four of the most common classifications.

Hollow Blocks

Blocks which contain one or more formed voids which fully penetrate the block

Solid BlocksBlocks which contain no formed voids

Block Walling: Block Classifications

Special BlocksBlocks which are designed and manufactured for a specific purpose and which have a shape

and size which varies from standard

Cellular BlocksBlocks which contain one or more formed

voids which do not fully penetrate the block

Block Walling: Bonding Arrangement

Block walling is generally build with a half-bond as this provides the most stable bond. There

should be no less than a quarter bond used at any point on the block wall. The wall shown

above is a standard build utilising full, half and quarter blocks. The quarter blocks are known as

closers and their purpose is to maintain the half bond at a return corner.

Half block

External return

Internal return

Foundation

Closer

Full blockStop end

Block Walling: Structural Stability

When masonry units are bonded incorrectly there is an increased likelihood that the structure

will fail when subjected to an additional load (e.g. the load of the structure, wind loads etc).

Stacking blocks one atop the other is known as risbond. In the animation above you can see

what happens when a load is placed onto the block at the top of the structure. It is for this

reason that we bond blocks together as a bonded structure will evenly distribute the combined

loads to foundation level.

Block Walling: Damp Proof Course

The damp proof course is installed a minimum of 150mm above ground level on a block wall.

The purpose of the damp proof course is to stop moisture being drawn up through the wall from

the ground in a process known as rising damp. Materials suitable for use as a damp proof course

include sheet lead and copper, bitumen, polyethylene, bitumen, rich polymer, mastic asphalt,

dense (engineering) bricks and slates.

Minimum 150mm above ground level

Block Walling: Expansion Joints

The purpose of expansion joints, or vertical movement joints, is to allow blockwork to expand

and contract without cracking. These joints should be located at areas in the wall that are

susceptible to cracking or are under continuous stresses. In lightweight blocks the maximum

distance between expansion joints is 6m. This increases to 9m when dense blocks are used. The

continuous vertical joint is normally between 10mm-15mm and is filled with a compressive

foam and sealed with a mastic sealant.

Compressible material

Mastic sealant

Block Walling: Compressive Strength

Dense LightweightSuper

Lightweight

Concrete blocks are classified by their compressive strength. This is their ability to

withstand compression before showing signs of fatigue.

Dense: Compressive strength between 1850kg/m² and 2100kg/m²

Lightweight: Compressive strength between 1000kg/m² and 1500kg/m²

Super Lightweight: Compressive strength between 850kg/m² and 1000kg/m²

Commonly available unit strengths of aggregate concrete and aircrete units include (all

units in N/mm2) 2.9, 3.6, 7.3, 8.7, 10.4, 17.5, 22.5, 30.0 and 40.0.

Compressive strengths: Source BS 6073-2:2008

Block Walling: Tolerances

D1 D2 D3 D4

Concrete blocks are also classified by the tolerances to which they are manufactured.

The table shows what each of the categories mean:

Tolerance Category

D1 D2 D3 D4

Length +3-5

+1-3

+1-3

+1-3

Width +3-5

+1-3

+1-3

+1-3

Height +3-5

+/- 2 +/- 1.5 +/- 1

Limit deviations in millimetres: Source BS EN 771-3:2003

Brick and Block Walling: Uniform Beds and Joints

The mortar between the blocks is designed to allow for small differences between the adjoining

beds and joints. Mortar beds and joints are uniform (the same size) in block walling. The width

of beds and joints is normally 10mm.

Brick Identification

The three faces of a brick are known as the header face, the stretcher face and the top bed.

Brick Dimensions

The standard dimensions for a brick are 215mm x 102.5mm x 65mm.

Brick Classification

Common Bricks are of low quality and low compressive strength but are useful for internal walls which will not be seen. They have no uniform colour, texture or appearance.

Facing Bricks are of high quality and uniform appearance. They are generally used externally in areas of “seen” brickwork.

Engineering Bricks are high in compressive strength and have low water absorption. They are particularly suited to use below ground level and in areas with exposure to water.

Brick Classification

Handmade Bricks are produced individually by an operative pressing clay into a mould. This means that they are more time consuming and expensive to produce.

Imperial Bricks are made to the dimensions used prior to decimalisation. Although larger and no longer used as standard, they are particularly useful for work that is to match original brickwork in an older building.

Reclaimed bricks are bricks which have been removed from a demolished building to be reused in a new project. Because it is usually older buildings which are demolished, the majority of reclaimed bricks are imperial sizes.

Building to Gauge

It is essential to consider the height of the wall when building. Bricklayers use a gauge rod to

ensure that the beds of mortar between each brick are uniform and to monitor the overall

height of the wall as each course is laid. Gauge rods are generally made by the bricklayer using

timber but they can also be bought in stainless steel.

Racking Back and Stopped Ends

The image on this slide shows a half brick wall with a stop end and racking back. This method of

construction is commonly used by bricklayers to build plumbings which allow them to plumb

either end of the wall and build to a line in the middle of the wall. This process is much quicker

than building the wall one course at a time.

Return Corners

The image on this slide shows a half brick wall built with a return corner. This means that the

wall turns (usually 90°) and continues in another direction. The bond remains unchanged and

that the course height remains constant on the return.

Toothing

The image on this slide shows a half brick wall which has a stop end and is toothed. The

purpose of toothing the brickwork is to allow for plumbings to be taking higher than a racking

would normally allow. You should however try to avoid toothing brickwork to a significant

height.

Brick Bonds: Stretcher Bond

Stretcher bond consists of bricks laid with the stretcher face exposed with a half bond. This

means that the centre of each brick is directly above the joint separating the two bricks on the

course below.

Brick Bonds: English Bond

English bond consists of alternating course of stretchers and headers. A quarter bond is

maintained by incorporating queen closers in every second course. English bond is generally

used in one brick walling.

Brick Bonds: Flemish Bond

Flemish bond consists of courses of alternating stretchers and headers. A minimum of a

quarter bond is maintained at all times. This bond is generally used on one brick walling.

Brick Bonds: Header Bond

Header bond consists of courses of headers maintained with a quarter bond. This bond is

generally used in one brick walling.

Brick Construction: Step 1

Step 1: On a short length of wall the bricks are laid out in a dry bond (without mortar) to ensure

that the correct length is achieved and that the correct number of bricks are used. On longer

walls it becomes more effective to calculate the number of bricks required.


Step 2: A bed of mortar is laid down using a bricklayers trowel. The mortar bed should be

roughly the same height, width and length of the first course of the wall. It is often useful to

chalk or pencil a mark on the foundation to guide the positioning of the first course.


Step 3: A single brick is positioned at either end of the length of the wall. Each brick is checked

for position, plumb and level. Minor adjustments are made to ensure the bricks are perfectly in

alignment.


Step 4: A string line is fitted in alignment with the top arris of each of the end bricks. This

enables the mid section to be built without having to plumb and level each individual brick. It is

essential that the line is pulled tight to avoid sagging in the middle.


Step 5: The mid section is filled with bricks to form the first course. Each course is checked for

level and the mortar joints should be filled. When a joint has not been properly filled it is known

as having been tip jointed. This is very poor practice and can reduce the future integrity of the

wall.


Step 6: A racking is build at either side of the wall. The racking is checked for plumb at the stop

end and for gauge on each course. Checking for gauge ensures that the wall is built to the

correct height. Each course is also checked for level.


Step 7: A string line is set in alignment with the top arris of the second course and used as a

guide for the bricks in the mid-section of the second course.


Step 9: The string line is moved in alignment with the arris of the top course and used as a guide

to complete the wall. In longer and higher walls the process of racking and working to a line is

repeated as often as is necessary.

Block Walling: Mortars

When setting out a job it is important to have the bricks or blocks and the mortar close at hand.

The image above shows a typical set-up that would be repeated along the length of any wall to

be built. Note that the bricks have been stacked in alternating directions to reduce the likelihood

of them falling over.

Brick and Block Walling: Joint Finishes

Mortar application styles vary and can alter the appearance and longevity of the wall. The next

selection of slides show common pointing and jointing styles used in brick and block walling. It is

important to be able to recognise and replicate them if you are working to a specification.

Joint Finishes: Flush

The flush finish is achieved with a mastic or flat pointing key. The mortar is left flush with the arrises of the brickwork or blockwork to provide a good seal and minimise rain penetration.

Joint Finishes: Recessed

The recessed finish is achieved with a brick jointer or flat pointing key. The mortar is kept 5-10mm from the arrises of the brickwork or blockwork to make the arrises more pronounced

(stand out). This style of pointing is aesthetically pleasing when a high quality of workmanship is achieved but does not provide the same level of water protection as flush pointing.

Joint Finishes: Rounded

The rounded finish is produced with a rounded jointer to leave a half round concave mortar bed/joint. This style of finish acts to shed water from the wall and provides an aesthetically

pleasing finish. It is the most common of brick mortar finishes in Scotland.

Joint Finishes: Weather Struck

This finish is designed to shed water running down the wall and protect the brickwork. It is carried out using a flat pointing key and the beds are angled from the top arris of the lower

course to a recessed point from the bottom arris of the brick above. The joints are filled flush to the arrises of the brick.

Joint Finishes: Reverse Struck

This finish is carried out using a flat pointing key and the beds are angled from the bottom arrisof the upper course to a recessed point from the top arris of the brick below. The joints are filled flush to the arrises of the brick. The finish is normally avoided as it exposes the top arris of each

brick to weathering and can lead to accelerated decay.

Education

Concrete Block Walling