Installing Carpeting over Concrete
You can install carpeting over concrete provided the necessary site conditions exist, the cement floor is prepared correctly and moisture and alkalinity testing is properly performed
The environment in which the carpet is to be installed must be controlled with the temperature between 65° F and 95° F (18° C and 35° C) and the relative humidity between 10% and 65%. The slab temperature should not be less than 65° F (18° C). These conditions must be maintained for at least 48 hours before, during, and 48 hours after the installation.
The concrete must be inspected to determine the special care that might be required to make it a suitable foundation for carpet. All cracks, holes, joints, and protrusions must be adequately addressed to ensure a smooth, finished appearance and prevent accelerated wear.
Concrete must be cured, clean, and dry, free of paint, dirt, grease, oil, curing or parting agents, and other contaminants, including sealers, that may interfere with the bonding of the adhesive.
Whenever a powdery or porous surface is encountered, a primer compatible with the adhesive to provide a suitable surface for the glue-down installation should be used. Patching compounds must be compatible with the adhesive selected and latex- or polymer-fortified. Manufacturer’s recommendations for patch thickness should not be exceeded. Large patched areas must be primed.
Primers – The use of primers on floor surfaces is generally not necessary except for sanded, dusty, porous, or acoustical surfaces. Priming cannot overcome moisture conditions and must not be used for that purpose. When used, primers must be thin, fast drying, and compatible with adhesives, which should be applied only after primer is dry.
Where lightweight or acoustical concrete is used, refer to the manufacturer’s recommendations for the proper primer to be used before carpet is installed.
Liquid Adhesive Removers – There are liquid adhesive removers available that will effectively remove cut-back or emulsion adhesive residue from subfloors; however, there is evidence these products may adversely affect the new adhesive or the new floor covering. Any residual of these products left in or on the concrete slab is capable of causing a failure. The use of these removers may void all applicable warranties.
Testing of Concrete Subfloors Prior to Adhesive Installations
The owner or general contractor must submit to the flooring contractor a written report on moisture and surface alkalinity of the slab to determine its suitability as a substrate for the material to be installed.
Concrete floors, even with adequate curing time, can present an unacceptable moisture condition by allowing excessive amounts of moisture vapor to pass through to the surface. This can be a problem even on suspended concrete floors. All concrete floors should be tested for moisture emission rate by utilizing an anhydrous calcium chloride moisture test kit available from installation supplies and accessories distributors.
This quantitative method is very precise and must be conducted carefully, with strict attention to the test kit manufacturer’s detailed instructions. Moisture emission rate is expressed in lbs/1000 sq ft/24 hours. Because the calcium chloride test for emission rate requires 3 days to conduct, proper installation planning is a must.
As a general guideline, an emission rate of 3 lbs (1.4 kg) or less is acceptable for most carpet. In the range from 3 lbs to 5 lbs (1.4 to 2.3 kg), carpet with porous backings can usually be installed successfully; but the risk of moisture-related problems increases. Since some floor covering products are less tolerant of moisture than others, always consult the individual manufacturer to determine the emission rate for specific products.
A pH range of 5-9 is satisfactory. A reading above 9 requires corrective measures. Consult the adhesive manufacturer for recommended testing and corrective procedures.
Source of information: CRI-104, Standard for Installation of Commercial Carpet.