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Concrete Relative Humidity

The newest concrete test method in recent years for floor products is in-situ (in-concrete) relative humidity testing.  This is the only test method that determines the concretes dryness properties within the concrete using small sensitive relative humidity probes as known in technical documents as ASTM F2170. 

A small relative humidity probe is inserted into the concrete slab based on the thickness of the concrete.  The HVAC system should be balanced and interior conditions maintained during testing process.  Concrete slabs are drilled based on 40% of their thickness for all floors levels.  Concrete on elevated (upper floors) are drilled 20%, of the thickness when no metal deck is used to hold the concrete into place from below. 

The number of test holes are based on the amount of floor products to be used on the project.  The proper test rate is three (3) tests for the first 1,000 square feet and one (1) additional test for each 1,000 square feet thereafter.  Testing at this rate is used to capture the various concrete pours used during the buildings construction and verifying tests at many locations to determine the concretes dryness for flooring.  A common sampling is 13 tests for projects with 10,000 square feet of flooring. 

The results are expressed in relative humidity percent for each test location.  The scale for this test method is 0 to 100%RH.  Additional information is required to properly report results and can be easily documented using our online calculator at

The industry has determined that a 75% relative humidity result (or less) is acceptable for all floor products.  However each manufacturer has a different marketing position on relative humidity and the amount each floor will tolerate.  Please keep in mind that all relative humidity probes have an accuracy of 2 to 3% and a reading of 95% may actually be a high of 98%RH or low of 92%RH.  We recommend over estimating the readings since you will be installing a non-breathable flooring system that will cause the RH to be increased after the floor is installed.     

A higher relative humidity result increases the potential for dampness (condensation) to occur under the flooring system after the product is installed.  The increased dampness causes the concrete’s natural alkaline levels to reach surface and this new elevated alkalinity-pH concentration is the destructive force that damages the flooring products.

Check List

1) Clean the concrete surface of curing compounds, sealers and adhesives.

2) Verify the HVAC is balanced to properly allow the moisture vapor escape from the concrete.  This is the ideal testing conditions per ASTM F1869.  Tests performed during non-HVAC controlled periods are not valid results.

3) Perform three (3) tests for the first 1,000 square feet and one (1) additional test for each 1,000 square feet of flooring thereafter.   Example: 10,000 square feet of flooring = 13 test results

4) Document your results in accordance with the following at each test location:

 5) Verify alkalinity-pH results at each test location.  This is important due to concrete alkalinity-pH being the destructive force that damages the flooring system.  It’s like salt water under your floor!