Moisture Testing Concrete Floors: Why it’s Important and How to Do it

Moisture Testing Concrete Floors: Why it’s Important and How to Do it

Concrete moisture testing is vital for flooring professionals, but many mistakes and assumptions are made that may increase the risk of issues going forward with moisture in your concrete.


While concrete often appears dry and hard, it’s full of moisture, as it starts as a liquid. Even after it hardens, moisture can continue to pass through the concrete for years, which can really affect your floors.

Many people believe that if the concrete surface is dry, the slab is dry.

As states, “Trapped moisture creates havoc that you do not need:

  • Moisture is conducive to the growth of mold and mildew.
  • Moisture can cause organic flooring materials (such as solid hardwood, engineered wood, cork, or bamboo) to degrade or rot.
  • Moisture can cause many types of flooring to bow, warp, or bubble.

You don’t want to run into any of these issues in your commercial facility, so it’s vital that the concrete is tested properly and by professionals.


Even after the concrete has hardened, it remains porous, so it’s important to do these tests with a professional.

Two tests that should be done to measure vapor emission. The first was developed by the ASTM Committee for Protective Coatings and Lining Work for Power Generation Facilities’ Subcommittee on Application and Surface Preparation. To use this method, ASTM D 4263, “Standard Test Method for Indicating Moisture in Concrete by the Plastic Sheet Method,” a plastic sheet is tightly taped to the concrete. After 72 hours, a humidity reading is taken under the plastic with a dew point hygrometer.

Depending upon the surface treatment that will be applied, a professional should tell you if the humidity released is acceptable for that treatment.

For most flooring, the humidity should be below 80% and the floor underneath the plastic should NOT be damp or discolored.

The second test is the ASTM F 1869, “Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride,” and it was standardized in the 1990s by the Subcommittee on Practices of the Committee on Resilient Floor Coverings. However, it was originally developed in the 1950’s by the Rubber Manufacturers Association.

This test requires three separate tests for the first 1000 sq. feet, with additional testing for the rest of the floor. This test is testing for moisture that’s being emitted from under a sealed portion of concrete. Instead of measuring humidity, this test captures the moisture levels in calcium hydroxide. As each of the calcium hydroxide tests are being set up, a sealed packet of calcium hydroxide is emptied into a small container and weighed. The container is then placed on the concrete under an enclosure and left open to the air under the enclosure for 72 hours. After this time, it is again weighed; the increase in weight indicates the weight of the moisture emitted by the slab over that time.

The test results end up being shown as the number of pounds of water being emitted per 1000 sq. feet of floor.

Remember: No single test can tell you everything you need to know and it’s important that testing is performed in a stabilized environment that will represent the conditions the building will be at while occupied and open for business.

For even more great information about this, refer to The Concrete Constructions Article, “How to Moisture Test Concrete.”

It’s important to note that there are also technology instruments with software that can aid in providing accurate results for moisture in the concrete.


One option we recommend is Concrete Epoxy Coatings. In a blog post by, you can read why epoxy coatings are great for concrete floors. These include:

  • To improve chemical resistance: An epoxy can help make a concrete slab more chemically-resilient to external elements.
  • To create a non-skid surface: In this way, the concrete epoxy acts as a simple surface treatment, removing the slide from the floor.
  • For aesthetics: More and more, concrete flooring is treated as a design feature. Just keep in mind that stamping, staining or specialized covering (such as terrazzo) requires stable concrete subfloor moisture content in order to work properly. Countless aesthetic flooring projects have been ruined by undue haste.

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