Testing paradigms for concrete slabs
All scientific tests generally produce results that are either subjective or objective. Furthermore, the dependent variable being measured generally occurs as a result of a stimulus that is either static or dynamic in nature. Moisture vapor emission is dynamic in nature. The vapor moving off the top of the slab (and into the flooring bond layer) is actively different than moisture contained in the slab. A moisture test report will objectively state the slab moisture emission condition. Therefore, a good moisture test is one that produces an objective result from measuring a dynamic situation.
Visual Appearance of the concrete can not describe a moisture condition, other than assume it exists when efflorescence is present. No human can see topical moisture vapor emission.
Concrete Slab Age is meaningless. Emission occurs at some level with 50 year old concrete.
Mat Tests are usually conducted by duct-taping a 3x3 foot sheet of plastic to the slab surface. After 24 hours, it must be judged if a problem exists by examining condensation under the plastic. Although a handy test, it is not objective, or sensitive enough to identify a condition that could cause a failure to a flooring system.
Bond Tests are usually conducted by installing a 3x3 foot piece of specified flooring directly over wet adhesive, every fifty feet. After a specified time, an inspection is made to see if the material has bonded and if the adhesive has dried. This test is very useful in determining adhesion problems if contaminants are present on the slab surface. However it is not a quantitative test of the slab moisture vapor emission.
Electronic Meters measure content moisture in the slab, usually in percentages. Some meters probe deeper into the slab than others. Since concrete can have electrical properties that can bias the test, it is often useful to place a heavy rubber mat over the slab for a day before testing to simulate the moisture entrapment that occurs under a floor, and then compare the results to an open slab area.
Chemical Chip Tests are of two types, those which measure moisture content in percentage, and those that determine alkalinity conditions. Alkalinity tests are highly informative in providing information about the acceptability of relatively neutral pH adhesives to characteristically high pH concrete.
Calcium Chloride Tests are practical, well established and widely acceptable tests for dynamic moisture. The test results have directly reflected industry-wide standards for concrete moisture vapor emission levels for decades. (FST recommended test) click here for Calcium Chloride testing materials