A. Jim Hamrick responds: There are two "subjective" tests that can be used to check for the presence of excessive moisture levels in a slab on grade.
The simpler is the "Rubber Sheet/ Plastic Mat Test." Using duct tape, carefully tape the edges of a 2x2-foot piece of 4-mil poly to the slab for 72 hours. If you observe any moisture droplets or surface color darkening of the slab, excessive moisture is present.
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