IB91 - Applying Moisture-Sensitive Floor Coverings and Adhesives to Concrete Slabs

8/6/2019 IB91 - Applying Moisture-Sensitive Floor Coverings and Adhesives to Concrete Slabs

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IB 91: Applying Moisture-sensitive Floor Coverings andAdhesives to Concrete Slabs Page 1

INFORMATION BULLETIN: IB 91

Applying Moisture-sensitive Floor Coverings andAdhesives to Concrete SlabsIntroductionThe Help Desk at the Cement and ConcreteAssociation of New Zealand receives a number ofcalls each year asking about moisture in concreteslabs that are to be overlaid with moisture-sensitive flooring materials.

Moisture in concrete floors can adversely affectflooring materials and the adhesion of floorcoverings such as sheet vinyl, tiles, timber stripsand carpet. For this reason, floor-covering andadhesive manufacturers often stipulate themaximum moisture content or relative humiditythat a concrete slab can have before the floorcovering or adhesive can be applied. The dryingtime of the concrete floor should therefore beconsidered during the design, planning andexecution of a project.

The purpose of this Information Bulletin is toprovide guidance to designers, specifiers andcontractors on this subject.

Moisture in ConcreteWater is added to concrete for two reasons:

(a) to hydrate the cementitious materials, and(b) to make the concrete sufficiently workable so

it can be satisfactorily mixed, placed,compacted and finished.

A typical concrete slab may have a cement contentof around 250 kg/m3 and a water:cementitiousmaterial ratio of 0.65. When this is the case, acubic metre of concrete will contain approximately160 kg of water. However about 40% of this wateris chemically bound with the cement (as a result ofhydration), which leaves around 95 kg of

evaporable water in a cubic metre of concrete.(Note: this figure excludes any water added duringcuring or from other sources, such as waterabsorbed from the sub-grade, condensation, orfrom falling rain.) In other words, the minimumquantity of evaporable water in a 100 mm thickconcrete floor slab is typicallyaround 10 litres per

square metre. This quantity increasesproportionally with the depth of the floor slab. Thatis, the minimum quantity of evaporable water in a150 mm concrete floor slab is typically around 15litres per square metre.

Effects of Moisture on FloorCoverings and AdhesivesMoisture in concrete slabs can adversely affect the

installation and performance of moisture-sensitivefloor coverings and adhesives. This can lead toproblems such as delamination, blistering, stainsand mould, and the breakdown of flooringadhesives as water vapour tries to escape.Impervious floor coverings, therefore, must not belaid until the concrete is sufficiently dry. It is vitalto ensure that the concrete slab is at or below themaximum specified moisture content or relativehumidity before moisture-sensitive floor coveringsor adhesives are applied.

Effects of Alkalis on Floor Coveringsand AdhesivesFreshly-placed concrete has a high alkalinity (pH).However, this alkalinity gradually reduces as theconcrete reacts with carbon dioxide from theatmosphere, in a process know as carbonation.Initially a thin layer of carbonated concrete isformed on the surface, but the depth increases withtime as the concrete is exposed to carbon dioxide.


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The presence of alkalis can be problematic as theycan break down adhesives and also causemicrobial growths that degrade the floor coveringitself. It is therefore important that flooring isinstalled on a concrete surface only after it hascarbonated sufficiently, and only after the concretehas dried sufficiently so that moisture does not

carry alkalis to the surface.

A procedure for determining the alkalinity of theconcrete is provided in Appendix B of AS/NZS2455.1:2007. The instructions of the manufacturer/supplier of the subfloor primers, adhesives, andfloor coverings should provide information on thepH at which installation should proceed.

Flooring Suppliers SpecificationsSuppliers and manufacturers of flooring materialsin New Zealand acknowledge the high risk thatexcess in-slab moisture poses for the satisfactoryinstallation and ongoing performance of theirproducts. At the time of publication, suppliers offlooring products require the following conditionsfor safe installation of their products:

1. Resilient flooring products (vinyl, linoleum,cork, rubber, etc) and all carpet must complywith Standards AS/NZ 2445:1 and AS/NZ 1884

(concrete slab moisture content less than 75%relative humidity, as measured by ahygrometer).

2. Timber (solid or engineered) overlay mustcomply with BRANZ Bulletin BU506 (concreteslab moisture content less than 70% relativehumidity, as measured by a hygrometer).

Consult the flooring product manufacturer to ensurethat the slab moisture content will not compromisethe products performance.

The New Zealand Building Code(NZBC) and New ZealandStandardsClause 10.3.1Concrete slab on ground General of

Acceptable Solution E2/AS1, External Moisture ofthe New Zealand Building Code stipulates thatevery concrete floor slab on the ground shall have a

damp-proof membrane (DPM) laid between theground and the slab, or between the top of the slaband a concrete floor topping that is no less then 50mm thick. The DPM material shall be bituminoussheet, polyethylene (polythene) sheet or rubberemulsion, as specified in NZS 3106 or 4229.

Acceptable Solution E2/AS1 also stipulates thatconcrete slabs shall be cast on a 75 to 600 mmthick granular base.

Clauses 1.5.3Adhesives and 2.4Conditions of FloorCoverings and Subfloor of AS/NZS 2455.1 specify,the following (among other things) for textile floorcoverings:

Clause 1.5.3 Adhesives The choice of adhesive shall be made by

consultation between the contractor and themanufacturers/ suppliers of the selectedunderlay, floor covering, and adhesive.

Only adhesives suitable for use in buildingswith relative humidity of 75% or more shall beused in such atmospheric conditions, andshall be used in accordance with theinstructions of the manufacturers of the floor-covering and adhesive.

Curing compounds, release agents andsurface treatments on the subfloor should beremoved prior to the application of trowel-applied levelling compounds or theinstallation of flooring.

Clause 2.4 Conditions of Floor Coverings andSubfloor Before installation, the floor-covering shall be

at the same temperature and relative humidityas the area where it is to be laid.

The preferred ambient temperature atinstallation shall be between 10 and 35C, butreference shall be made to the manufacturersrecommendations.

The floor-covering shall be installed onlywhere the relative humidity of the area doesnot exceed 75% or fall below 30%.

Heating units shall not be used to dry theconcrete subfloor before the concrete has


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been cured for one month after placing. Theconcrete shall be allowed to dry out slowly tominimise cracking.

All sub-floor surfaces shall be dry, smooth,plane, sound and clean. Dryness shall beconsidered satisfactory when the relative

humidity, determined by the hygrometer test,does not exceed 75%.

Measuring Moisture in a ConcreteSlabAppendix B (Informative) of AS/NZS 2455.1:2007Textile floor coverings Installation practice General sets out some general information andmethods for determining the dryness of concrete

subfloors.

The Appendix discusses the variables that cansignificantly affect the reliability of testing systems,and stresses that all moisture tests should becarried out in accordance with the instrumentmanufacturers instructions. All testing instrumentsshould be calibrated regularly in accordance withthe manufacturers instructions. Procedures for thehygrometer test and the capacitance test aredescribed in Appendix B of AS/NZS 2455.1.

Hygrometer TestThe hygrometer test is used to estimate the egressof moisture by measuring a small amount ofcontained air at the surface of, or within a drilledhole in, a concrete slab. The surface test uses ahumidity measuring device inside a vapour-proofbox to measure the relative humidity of thecontained air in a 16-hour period. The vapour-proofbox is sealed to the concrete slab with a non-waterbased putty. The in-slab test uses a vented plasticinsert (sealed at the surface) and uses a testing

procedure similar to the surface method.

According to Standards AS/NZ 2455:1, AS/NZ 1884and BRANZ, the hygrometer method is the mostreliable method of assessing the degree of drynessof a concrete slab. However, the surface test willproduce a lower reading than the in-slab test so isless indicative of slab moisture.

Capacitance TestThe capacitance test is used to estimate the

moisture content of concrete through the emissionand reception of low frequency energy waves,typically by placing an energy transmitter/receiveron the surface to be tested. The approximatesaturation of the substrate to a nominal depth ofup to 10mm is calculated using predeterminedcalibrations.

Although the capacitance test provides fast andimmediate measurements of concrete, the test isless precise than the hygrometer test. Thecapacitance test is best suited to an initial testingregime to indicate the possibility of excessmoisture.

Calcium Chloride TestThe calcium chloride test involves placing an open

dish containing a specified mass of calciumchloride under a plastic dome that is sealed to theconcrete slab. The moisture vapour emission rate(MVER) is determined by calculating the percentageincrease in the mass of crystals due to moisturevapour absorption after 60 to 72 hours.

The standard test method is set out in ASTM F1869-04. Appendix B of AS/NZS 2455.1:2007states that this test is not recommended asinsufficient experience has been gained of its use.

Polythene Sheet TestThis test is a qualitative field test rather than astandard test and is therefore of limited use. Itinvolves tightly taping a large (say 450 x 450 mm)polythene sheet to the concrete slab for at least 16hours. The slab is still too wet to apply moisture-sensitive floor-coverings if condensation formsunder the polythene sheet. However, the test canprovide false negative results, and therefore theabsence of moisture under the polythene does notalways mean that the slab is acceptably dry. Forthis reason, the dryness should be determined bythe standard (hygrometer) method.

Electrical Resistance TestThe use of electrical resistance testing, wherecurrent is passed between to probes inserted intothe concrete slab, is not a suitable method forassessing moisture content. Significant variablesin the makeup of concrete mean the test results arehighly unreliable.


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Drying Rates Rules of ThumbMany variables control the drying rates of concreteslabs, including initial moisture content, porosity,temperature, relative humidity, and air velocity.Drying does not progress at constant rates; the first

water evaporates relatively quickly, while the lastwater comes out more slowly. BRANZ haspublished the following rule of thumb guidelinesfor the drying time of concrete slabs to reach theappropriate relative humidity in well-ventilatedbuildings:

Concrete thickness (mm) Drying time (months)75 3

100 4

150 9

200 16

Another oft-quoted rule of thumb is to allow onemonth drying time for every 25 mm depth ofconcrete. It is important to note that this generalrule is applied from date of close-in (weather tight),not from date of placement. However, as pointedout previously, the last water to come out that is,

water from the deeper sections of the slab actually comes out more slowly than the waternearer the surface.

It is important to note that drying times varyconsiderably with factors such as weatherconditions, air temperature, humidity and airmovement. Also, floor coverings can sometimes belaid successfully in less time than indicated above.

Avoiding Delays to Floor CoveringOperationsDrainageProtection against water ingress can be provided byensuring that proper drainage away from the slab isconsidered during the design stage of a project andis provided during the construction phase.

Capillary BreakA granular base under a concrete slab on grade willact as a capillary break so that moisture rising fromthe underlying soil cannot be absorbed by the

concrete slab. NZBC E2/AS1 stipulates such agranular base layer - see The New Zealand BuildingCode (NZBC) and New Zealand Standards, above.

Damp-proof Membrane (DPM)A DPM under the concrete slab is designed to

prevent moisture entering the slab from beneath.The NZBC requires interior concrete floors on theground to have a DPM see The New ZealandBuilding Code (NZBC) and New Zealand Standards,above.

Concrete Mix DesignThe concrete mix should have as low a water-cementitious material (w:cm) ratio as practical inorder to minimise the quantity of evaporable water.

For example, reducing the w:cm from 0.65 to 0.50will lower the quantity of evaporable water byaround 35% (i.e. from 95 to 65 kg/m3 for a concretemix with a cementitious material content of 250kg/m3 and a w:cm ratio of 0.65). Water-reducingadmixtures can be used to maintain adequateworkability. Moreover, concrete with a low w:cmratio that includes a supplementary cementitiousmaterial, such as fly ash, will have a reducedpermeability to vapour transmission.

Rain and Other Sources of WaterAll practical measures should be taken to protectthe concrete slab from rain and other sources ofmoisture prior to installing the floor coverings.

CuringMoist curing will increase the time it takes aconcrete slab to dry. Moreover, the use of curingcompounds should be avoided refer clause 1.5.3(e) of AS/ NZS 2455.1:2007. Curing the concreteunder an impermeable sheet, in accordance with

Clause 7.8.2(e) Curing and protection/ unformedsurfaces of NZS 3109:1997, is recommended.

Forced Slab DryingWhile the use of dehumidifiers and driers canappear to accelerate the drying process, the neteffect on the moisture content of the slab isnegligible unless the process is maintained for aconsiderable period, generally several weeks.Caution should be exercised when testing a forced-dried slab to ensure that sufficient time is given for


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the moisture content to achieve relative equilibriumbetween the bottom, centre and top of the slab.AS/NZ 2455:1 requires all air conditioning to beturned off for seven days prior to testing.

Applied Moisture BarriersWhere time constraints require, the excessmoisture emission of a concrete slab may bereduced through the application of a topical epoxyor co-polymer moisture vapour barrier. This type ofvapour barrier relies on the integrity and adhesionof the coating to the sub-floor. The performance ofthese coatings is highly dependent on the correctapplication, including the correct volume ofproduct per square metre and close attention to themaximum moisture content of the slab. Themanufacturers specifications should be carefullyfollowed. Caution is needed when treating cracks,cuts and/or joints in the slab, to ensure theperformance of the coating is maintained. Topicalepoxy or co-polymer moisture vapour barriers aretypically applied immediately prior to installingfloor coverings. Correct performance of the appliedcoating should be assessed through the use of asurface-mounted hygrometer after the coating hasbeen applied.

Slab ThicknessAccording to ACI Committee (see Source 4 ) slabthickness affects the time needed to reach a givenrelative humidity within the slab; a thicker slabrequires more time. See also Drying Rates Rulesof Thumb, below. However, slab thickness has noeffect on the time required to reach a givenmoisture vapour emission rate.

ConclusionsMoisture in concrete slabs can cause problems tomoisture-sensitive floor coverings and adhesives.The drying time of a concrete floor to be overlaidshould therefore be considered carefully during thedesign, planning and execution of a buildingproject to avoid problems.

To avoid problems, it is important to understandthe following: the sources of moisture in a concreteslab; the proper design of slabs, with carefulattention to detail; the Building Code andSpecification requirements; and the measurement

and testing methods. This knowledge can guide

the design, planning and scheduling of buildingprojects so that problems will be rare.

Sources and Further Reading1. Kanare HM, Concrete floors and moisture,

Engineer Bulletin 119, Portland CementAssociation, Skokie, Illinois, and NationalReady Mixed Concrete Association, SilverSpring, Maryland, USA. (2005).

2. Concrete Society Working Party, Moisture inconcrete and the performance of impermeable

floor coverings, Project Report No. 4, TheConcrete Society, Camberley, Surrey, UK.(2004).

3. Standards Australia/Standards New Zealand,AS/NZS 2455.1:2007, Textile floor coverings Installation practice General, StandardsAustralia, Strathfield, NSW, Standards NewZealand, Wellington.

4. Standards Australia/Standards New ZealandAS/NZS AS/NZS 1884:1985 Floor coverings Resilient sheets and tiles Laying andmaintenance practices, Standards Australia,Strathfield, NSW, Standards New Zealand,Wellington.

5. BRANZ, Bulletin BU506, Laying solid timber strip flooring on concrete slabs, BRANZ,Porirua, Wellington. (2008).

6. ACI Committee 302, ACI 302.2R-06, Guide forconcrete slabs that receive moisture-sensitive

flooring materials, American ConcreteInstitute, Farmington Hills, Michigan, USA.

7. NRMCA, Concrete in practice: What, why &how? CIP 28 Concrete slab moisture, NationalReady Mixed Concrete Association, SilverSpring, Maryland, USA. (2004)

8. BRANZ, Good Practice Guide Concrete Floorsand Basements, BRANZ, Porirua, Wellington.(2003).

9. Lee N, Is that concrete floor dry yet? Build,BRANZ, Porirua, Wellington. (March 2006).

10. NZS 3604:1999, Timber Framed Buildings,Standards New Zealand, Wellington.


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ISSN 0114-8826

May 2009. Cement & Concrete Association of New Zealand, Level 6, 142 Featherston Street, PO Box 448, Wellington, telephone (04) 499-8820, fax(04) 499-7760, e-mail [email protected], www.cca.org.nz.

Since the information in the bulletin is for general guidance only and in no way replaces the services of professional consultants on particular projects,no liability can be accepted by the Association by its use.

IB 91: Applying Moisture-sensitive Flooring Materials toConcrete Slabs Page 6

11. NZS 4229:1999, Concrete masonry buildingsnot requiring specific engineering design,Standards New Zealand, Wellington.

12. Suprenant B, Design of Slabs that receiveMoisture-sensitive Floor Coverings, Part 2:Guide to Specification Issues for Architects and

Engineers, Concrete International, FarmingtonHills, Michigan, USA. (April 2003).

13. Concrete Society, Concrete Advice No. 22,Moisture in Concrete Floors, The ConcreteSociety, Camberley, Surrey, UK. (2005).

14. Craig P and Donnelly G, Moisture Testing ofConcrete Slabs, Concrete International, ACI,Farmington Hills, MI, USA. (September 2006).

15. Craig P, Moisture Mitigation for ConcreteSlabs, Concrete International, ACI, FarmingtonHills, MI, USA. (August 2003).16. ASTM F 1869-04, Test Method for MeasuringMoisture Vapour Emissions of ConcreteSubfloors using Anhydrous Calcium Chloride,ASTM International, West Conshohocken, PA,

USA.

17. NZS 3109:1997, Concrete Construction,Standards New Zealand, Wellington.

18. CCAA Data Sheet: Moisture in Concrete andMoisture-sensitive Finishes and Coatings,Cement, Concrete and Aggregates Australia,Sydney, Australia. (2007).

CCANZ wishes to acknowledge the contribution of the New Zealand Flooring Industry TrainingOrganisation (Flooring ITO) and New Zealand National Flooring Association in the preparation of thisdocument. The Flooring ITO and NZNFA have endorsed this Information Bulletin.

Documents

IB91 - Applying Moisture-Sensitive Floor Coverings and Adhesives to Concrete Slabs