A concrete moisture meter (sometimes known as a damp meter) is a portable instrument used by installers of flooring for finding the moisture levels in concrete.
Concrete moisture meters have been used for many years to determine the moisture content in a variety of materials and substances. Moisture meters are used to measure the water percentage in a given material. The reading provided can then be used to ascertain if the concrete is ready for painting, if it is unexpectedly wet or dry, or might otherwise be in need of further drying time. Moisture meters were initially used for wood and paper products as these materials are extremely sensitive to their moisture content. Specific concrete moisture meters have developed from the technologies first used successfully in wood moisture meters.
Dedicated Concrete moisture meters are manufactured to be able to detect moisture to a depth of 1” of a concrete slab. They are intended to be used as a relative test. Moisture meters are used to perform as spot check at the surface of the concrete at particular locations. Tests at various points in on the floor should be carried out. The results provided by these various readings can be used determine the best place to carry out a concrete relative humidity test. Often the corners of the floor provide the highest readings and as such care should be taken to endure these are below 8% before applying floor paint.
At present, there is no ASTM standard for the use of concrete moisture meters to determine a final moisture content reading.
Concrete moisture meters, either non-pin or pin meters are affected by what it sees in the concrete. This can be anything from the density of the concrete and aggregate size to the chemical properties of the slab.
Uncovered concrete dries from the top down
As these meters just measure the top inch (at most) there is a good chance the concrete may be wetter further down. As a general rule, in addition to measuring the moisture content of the concrete surface it is vital that you allow freshly laid concrete sufficient drying time before applying concrete floor paint. We suggest as a rule of thumb that you allow 1 month per inch of concrete laid. i.e. a typical 6″ concrete slab should be left for six months prior to priming and painting.