What’s the best concrete moisture test method?

Flooring installers are increasingly aware of the importance of testing concrete slabs for moisture before installing their flooring. This awareness is inspired, in part, by flooring manufacturers that require such testing to qualify for warranty coverage. But what is the best method for performing that testing?

There are two main ASTM standards for testing the relative humidity (RH) of concrete slabs: ASTM F1869 - 16a and ASTM 2170. Let’s take a closer look at each in turn.

ASTM F1869

ASTM F1869, “Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride,” employs a method of measuring the moisture vapor emission rate (MVER) that has been around since the 1940s. A small container of calcium chloride (CaCl) is placed on the clean concrete surface and covered with a plastic cover. This apparatus is left in place for 60 to 72 hours, at which time the calcium chloride is weighed to determine the mass of moisture absorbed by it.

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The calcium chloride test is relatively easy and inexpensive to perform on a concrete slab (if an existing floor is in place, sections must be removed in order to perform the test). However, there are serious shortcomings. There is no practical way to calibrate the apparatus, making it difficult to compare results against a benchmark. Test accuracy can be impacted by ambient conditions or variability in slab surface preparation. In addition, it only effectively tests moisture vapor emissions near the surface of the slab and, therefore, does not provide an accurate MVER measurement. Despite these shortcomings, the ASTM F1869 test is still in use in the field, even though many floor manufacturers’ warranties do not honor calcium chloride test results.

ASTM 2170

ASTM 2170, “Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes,” takes a different approach to measuring moisture. As the name suggests, this method calls for small test holes to be drilled into the concrete slab at a depth 40% of the total thickness for slabs on grade (20% from each side of suspended slabs). For a 6-inch slab on grade, the bore hole would be approximately 2.4 inches. RH probes are placed in the holes, attached to a hygrometer (RH meter) to gather readings on a regular basis for a minimum of 72 hours.

While the ASTM 2170 probe test is a bit more involved and costly than the calcium chloride test, it provides more accurate measurements of moisture in concrete slabs over time. It is less likely to be affected by ambient conditions. And it provides information about moisture levels deep in the concrete slab, rather than simply on the surface. For these reasons, flooring manufacturers are increasingly recognizing ASTM 2170 as the “gold standard” for verifying the dryness of concrete floors prior to installation of their products.

Which moisture test is best?

It must be stated that any moisture testing is better than none. Before making any testing decisions, make sure to review the flooring manufacturer’s installation instructions and warranty information to see if they require or favor a particular approach.

Have questions about concrete floor moisture testing, moisture mitigation or which KOVARA®floor moisture barrier is the best option for your project? Get in touch with a flooring specialist at GCP Applied Technologies.


*Source: See the complete ASTM F710 standard

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