The moisture concentration in concrete needs to be tested before applying a coating or putting down flooring. The flooring could be ruined if the moisture concentration in the concrete slab is too high. Knowing the moisture content of your concrete can also give you information to choose the flooring that will work best.
There are three standard tests used to determine the moisture content in a concrete floor. You may need a moisture test to get a flooring warranty, or you may simply want the peace of mind that your concrete is ready for flooring installation.
The best way to get accurate moisture testing results is to have them done by a professional moisture tester. A moisture tester also interprets the results to help you make the best flooring decision.
The Plastic Sheet Test
Builders have used the plastic sheet method for decades. It’s a simple test that tells you if there is moisture in the concrete.
The test is conducted by taping an 18-inch square plastic sheet to your concrete slab. The square is left in place for 24 hours, and then the area underneath is inspected for dark spots and other signs of moisture.
This moisture test might not be accepted by flooring manufacturers for warranty purposes. It doesn’t tell you how much moisture is in the concrete, and it only tests the slab’s surface, not the deeper layers that could be hiding more vapour.
The Calcium Chloride Method
This test is performed with a dish of calcium chloride underneath a sealed dome. The dome and dish sit on your slab for 24 hours. Calcium chloride absorbs any moisture that rises from the concrete.
After the test, the dish of calcium chloride is weighed. The difference between the before and the after-test weight shows how much moisture is in the concrete.
The calcium chloride test is more likely to be accepted by flooring manufacturers for warranties. It still only tests the water in the surface of the slab.
The Relative Humidity Method
During the relative humidity test, holes are drilled into the concrete slab down to 40 percent of its total depth. Then testers insert a humidity probe into the holes, which reads the amount of moisture.
This test is one of the most accurate and is trusted by flooring manufacturers. You still might need other tests to comply with a flooring warranty.