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Specifications for Testing Moisture Vapor Emission

Concrete needs moisture testing every time flooring is changed

Millions, if not billions, of dollars are spent every year to replace, repair and correct floor covering problems related to excessive moisture and elevated pH levels of concrete floor slabs.

Proper moisture testing

Proper testing in advance of installing a new floor or replacing an existing floor is the only way of knowing the moisture condition of the concrete rather than guessing what it might be.

When should you test? Always. Test if it’s old or new concrete, even if the existing flooring material that’s installed looks in good shape. All concrete slabs should be tested for moisture regardless of age or grade level. On-grade, above-grade, below-grade – from the penthouse to the basement – if it’s concrete slab, test it.

Testing Methods

1. ASTM F 2170 – Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ probes, measures moisture inside a concrete slab

2. ASTM F 1869– Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous calcium Chloride, measure vapor emission at the concrete surface

Both testing methods provide valuable information, and it’s good idea to perform both in addition to the pH test. Usually these three tests are done at the same time and the data collected will provide a relevant understanding of the existing concrete slab’s moisture condition.

Moisture Tests: Calcium Chloride (ASTM F 1869) vs.
Relative Humidity (ASTM F 2170)


Calcium chloride test quantifies the moisture vapor emitted from the slab. This test has long been the standard in the United States where as the relative humidity (RH) test measures moisture conditions inside the slab. The relative humidity test is the standard in several other countries. The calcium chloride test generally indicates moisture conditions in the top region of the concrete slab, whereas relative humidity probes tell you what’s going on in the body of the concrete which is more useful in the long term. Please find below a quick overview of both calcium chloride and relative humidity tests.

calcium chloride test

The calcium chloride test, sometimes called the moisture vapor emission rate (MVER) test, is simple inexpensive and widely accepted. It takes advantage of the fact that calcium chloride absorbs moisture like a sponge. A small container of salt is weighed before and after it’s exposed to the concrete slab for 60 to 72 hours. The weight difference as a percentage of the original weight of the calcium chloride used gives the moisture vapor emitted by the slab. It is usually expressed in pounds per 1,000ft2of concrete per 24hours.

For accurate results, the test has to be conducted with the building at the same temperature and humidity level that it will be at when in use – which can be problem if the HVAC system isn’t operational, as is often the case during construction. Another limitation of the test is that its results reflect only the moisture in the top ½ inch to ¾ inch of the slab. Most of the moisture within the slab accumulates in the lower half, which can have twice as much moisture as the upper half.

relative humidity test

This test involves drilling a hole into the concrete and inserting a probe that measures moisture deep within the concrete slab. The results, expressed as a percentage of relative humidity rather than in pounds of moisture vapor, are read on a meter connected to the probe. While the relative humidity testing apparatus isn’t as sensitive to the ambient room temperature and humidity as the calcium chloride test, it’s still important that both the test hole and the probe be allowed to acclimate to the room’s conditions. ASTM calls for the probe to be left in place for 72 hours to allow taking the reading.

While the relative humidity test provides a more complete picture of what’s going on throughout the entire depth of the slab, the initial cost of the relative humidity test apparatus is substantially more than the calcium chloride test. It is ideal to conduct both the tests since each looks at a different part of the same picture.

Who should do the testing

There is much concern about whose responsibility it is to test the floor. The Floor Covering Industry White Paper Position Statement on Moisture Emission Testing recommends independent testing rather than assuming the floor covering installer, the general contractor or landlord/developer will do the right thing and test the floor.

Affective specifications

The best way for the owner to assure that the testing gets done is to write a testing specification themselves. A simple statement such as “install floor covering according to manufacturer’s instructions” is not enough. What is needed is to create a specification section regarding moisture testing that will leave no question about what testing is to be done, when the floor will be tested, who is to do the testing, how the results are to be reported and who will receive the copy of the test report.

Elements of specification

The elements of moisture-testing specifications should include:

Type of testing to be done – usually ASTM F 1869 and ASTM F 2170 moisture tests and pH testing per ASTM F 710

Number of tests – the standard calls for three tests for the first 1,000square feet and one test for each 1,000 square feet thereafter, but the owner may change the number of tests based on their needs.

Timing of testing – the temperature and humidity conditions are important and on new construction, testing should be done after the building is enclosed and the HVAC system is up and running. For a renovation project, the testing should be done at least a month prior to the scheduled floor covering installation, so there is adequate time for corrective measures to be taken if they are necessary.

Reporting – test reports should contain as much information as possible about the conditions at the time of testing, methodology of testing and test results. This is an important way to document not only the test results but the accuracy of the testing that was done. The specification should also identify who is to receive the report – the owner, general contractor, architect or all parties.

Mapping – the more sophisticated reporting done by some independent agencies will show the test results on a map of the facility, which can help the construction team identify problem areas in the floor.

Repair options – the report should include options for repairing a floor that exceeds the manufacturer’s limits.

The moisture testing specification may be standalone specification as part of a concrete floor slab section that details some of the key points of a concrete industry standard designed to prevent floor covering moisture problems. The details may include the need for the concrete to be dry, clean, smooth, and free of contamination, the inclusion of a proper water-cement ratio, the installation of a vapor retarder directly under slabs on or below grade, the use of moisture-retaining coverings for curing concrete and so on.

The solution

Concrete floor moisture-related failures continue to cost property owners a great of money and lost time. It pays for these parties to take charge of the process, requiring testing by independent agencies and creating detailed specifications that direct the entire construction team as to what is expected of them so potential flooring problems can be identified and solved in advance.

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