Is there a correlation between relative humidity percentage and moisture vapor emission rate measured with calcium chloride testing?
There is no correlation between the tests. Relative humidity testing is a measure of moisture condition in the concrete. When a floor covering is placed on top of a slab, it restricts evaporation from the top surface of the slab; moisture within the slab then distributes itself to achieve equilibrium due to temperature and chemical interactions from the top to the bottom of the slab.
In the long run, adhesive and flooring are then exposed to the equilibrium moisture condition at the top of the slab. The calcium chloride test does not reflect the long-term moisture situation that will be established by equilibration and can even artificially pull moisture out of the top few centimeters of the slab. Rapid RH®4.0 EX Smart Sensors measure the relative humidity that will exist after the floor is covered. See Measuring Concrete at the Correct Depth
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