Laminate floors are a great option for installing over a concrete slab. However, it is very important to take the appropriate steps for moisture protection to ensure a quality installation. Skipping this important step can result in peaked seams, cupping and/or buckling (see Photo 1). Even worse, the floor can expand to the extent that it lifts up, breaking the tongue and groove. New concrete slabs should be allowed to dry for at least 60 days. After moisture testing, they must be covered with a manufacturer-approved vapor retarder before installing a laminate floor.
Moisture Meter Test:Electrical impedance meters are one way to measure moisture and quickly survey the condition of a concrete slab. They’re also useful in searching for moisture problems that may occur at the perimeter of the room or around pipes that may be leaking below ground. Simply place the meter flat on the concrete and read the display. Measurements outside the specified range will require further testing (see Photo 2).
Calcium Chloride Test:Calcium chloride test ASTM F1869-09 produces quantified results of the amount of moisture vapor emitted from a 1,000-square-foot area (measured in pounds) over a 24-hour period. To be effective, the test site should be at the temperature and humidity levels experienced during normal use.
First, expose an area approximately 20” x 20” and remove all residual adhesives, curing compounds, sealers, paints and floor coverings. The best way to do this is with a grinder covered with a dust shroud attached to a vacuum (see Photo 3).
Second, leave the area exposed to ambient conditions for a minimum of 24 hours (See Photo 4).
Third, accurately weigh the anhydrous calcium chloride plastic dish included in the test kit (it typically weighs approximately 32 grams). Place the dish under a sealed plastic dome and leave in place for 60 to 72 hours (see Photo 5). When time has expired, remove the dish and immediately reweigh. Perform this test at least 3 times for the first 1,000 square feet and at least one additional time for each subsequent 1,000 square feet. Follow the formula provided by the test manufacturer to calculate the amount of moisture vapor emitting from the slab. If results are below the recommended emission rate (usually 3-5 pounds in a 24-hour period), you can proceed with the installation using a 6 mil poly film.
Relative Humidity Test:Test ASTM 2160 quantitatively determines the percent of relative humidity within a concrete slab for field or laboratory testing.
First, use a rotary hammer drill with a carbide-tipped drill bit to drill holes to the required depth (see Photo 6). For concrete drying from one side, drill the hole to a depth of 40% of the thickness of the slab.
Second, remove the dust from the hole using a vacuum cleaner (see Photo 7).
Third, insert a hole liner to the bottom of the hole. Place the stopper into the upper end of the liner and seal around the liner. Allow 72 hours to achieve equilibrium within the hole before making relative humidity measurements (see Photo 8).
Next, remove the stopper and insert the probe into the liner (see Photo 9). Allow the probe to reach temperature equilibrium before measuring relative humidity. The probe should be at the same temperature as the concrete before reading. The meter reading must not drift more than 1% relative humidity over five minutes. Record the relative humidity and the temperature to the nearest degree F. Also record the location of the hole within the structure and depth of the probe tip below the concrete surface. Perform three tests for the first 1,000 square feet, and at least one additional test for each additional 1,000 square feet. If the measurement is below the manufacturer’s recommendation, proceed with the installation using 6 mil poly film.