Moisture in concrete slabs is essential for curing. But it can be detrimental to the adhesion of floor-covering materials such as resilient tile or sheet flooring, paints, coatings and sealers. Flooring materials sometimes fail because the alkaline moisture in the concrete interferes with the bonding properties of the flooring or its adhesive. Therefore, it is wise to test the moisture condition of the slab before flooring is applied. The test should show that the slab is dry enough to accept the particular floor covering. The drying period required will vary with environmental conditions, type and thickness of concrete, and location of the slab.
The best way to determine if a slab is ready for flooring material is to test--rather than guess--the moisture condition of the slab. Three simple methods are commonly used: the polyethylene sheet test; relative humidity test; and the mat moisture and bonding test.
Various types of moisture meters are available to measure the relative humidity or moisture content within the concrete. Examples are: embedded meters; insert-meters cast in wells; and surface meters.