Three tests for moisture content in concrete:
- The first test is the calcium chloride test. The flooring industry considers a moisture vapor transmission rate of 3 pounds/1,000 square feet/24 hours safe for all flooring. The problem is that even low water-to-cement ratio concrete takes about 86 days to dry out to that safe rate, and that’s at a conditioned environment of 73 degrees and 50 percent relative humidity. This also assumes that the concrete is on an impervious surface — a vapor barrier with no holes in it.
- The second test measures the moisture retained in the concrete slab, which is done with moisture probes. Typically the safety level is 70 to 75 percent relative humidity. If the relative humidity is higher, then the pores of the concrete are starting to fill up with water.
- The third test is a direct tensile bond test. The minimum tensile strength recommended by the American Concrete Institute is 175 psi. The three tests together will help a contractor determine the risk/success level of an application over a high moisture concrete slab, he said.