"This test method covers the quantitative determination of percent relative humidity in concrete slabs for field or laboratory tests. The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard."
"Excessive moisture in floor slabs after floor covering has been installed can cause floor covering system failures such as debonding, peaking and deterioration of finish flooring and coatings and microbial growth. Manufacturers of such systems generally require moisture testing to be performed before installation on concrete. Internal relative humidity testing is one such method. Moisture test results indicate the moisture condition of the slab only at the time of the test and in the specific locations tested."
Citation: ASTM F2170-17, Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes, ASTM International, West Conshohocken, PA, 2017, www.astm.org
This ASTM standard requires a minimum of 24 hours for the testing duration.