As hard as many of us have worked to train and write about the importance of concrete moisture testing, many floors are still installed without conducting any tests prior to installation. If they are, then they are using what I call “the senses test” (“It looks dry,” “It feels dry,” and/or “It smells dry”), even though you can’t see, feel or smell moisture coming out of a concrete slab. ASTM F 710, Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring says, “All concrete slabs shall be tested for moisture regardless of age or grade level.” That means new or old, basement or 50th floor, ALL slabs!
When tests are performed, they are most often just using a moisture meter (which is not accepted by any resilient flooring manufacturers), or they may use a plastic sheet test or the calcium chloride test, often incorrectly. When floors fail because of moisture and the floor wasn’t tested, troubleshooters like myself go back to the specifications to see if the architect called for testing. Then, we go back to the flooring and adhesive manufacturer’s guidelines - where it is ALWAYS called for. The question at that point becomes who was supposed to test, and/or why wasn’t the floor tested? The whole situation gets ugly.
I am amazed how often I get calls from someone who gives me a concrete moisture meter reading and asks if it is okay to install a resilient floor, even though there isn’t a resilient flooring or adhesive manufacturer out there who will accept such a reading for a “go or no go” determination of a slab’s readiness to receive flooring. I also get asked what the correlation is between a concrete moisture meter and the calcium chloride test (there is no such correlation).
ASTM E 1907, Standard Guide to Methods of Evaluating Moisture Conditions of Concrete Floors to Receive Resilient Floor Coverings, has a section on how to use meters. It says, “Although a high reading…typically indicates high moisture content, a low reading…does not necessarily indicate more than surface dryness, as the concrete may have a higher moisture content below the surface. Conversely, a concrete with low moisture content but containing metal fibers could cause a high reading.” This points out the risks of relying on this method exclusively. Metal in the concrete can affect the readings and moisture below the surface is not detected. So, when DO you use a concrete moisture meter?
My research on the Internet did find a few mentions of the plastic sheet test (a plastic sheet taped to the floor for a day or two). The people referring to this method are, with all due respect, behind the times. The plastic sheet method is influenced by atmospheric conditions and is not accurate, so wet means wet, but dry may not mean dry. I have seen firsthand slabs that tested “wet” using more scientific methods and “dry” with a plastic sheet. Be careful - this method should not be used.
Most references to moisture testing in the reading I did and in manufacturers guidelines refer to the calcium Chloride Test (ASTM F 1869 Standard Test Method for Measuring Moisture Vapor Emission Rate (MVER) of Concrete Subfloor Using Anhydrous Calcium Chloride). There is an increasing amount of reference to a newer method, The Relative Humidity (RH) “Probe” Method (ASTM F 2170, Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes).
There are three key points to doing this correctly:
- The building has to be the same temperature and humidity it will be when the space is occupied (heat or air conditioning must be on);
- The surface of the concrete has to be cleaned by a gentle grinding before the tests go down;
- You need to wait 24 hours after grinding before putting the kits down.
Kanare is with the CTLGroup, one of the pre-eminent concrete testing labs in the country, and I have been honored to work with him as a fellow a volunteer on the ASTM F.06 committee on resilient Flooring. He wrote the groundbreaking book “Concrete Floors and Moisture.”
He goes on to say, “over the past 10 years, CTLGroup has investigated the performance of the MVER test method in the field and in the lab, and we have found that it suffers from several serious deficiencies.” He adds that there is no data from 50 years ago to determine why the kits are the size they are, and there is no research showing why the 3- or 5-lb. limits are so often used by flooring manufacturers. He also says “ambient conditions interfere with test results - warmer, more humid room air can yield higher MVER results even if the internal concrete moisture condition is unchanged.” He warns the test has only proven to measure moisture from the top 1/2- to 3/4-inch of the slab. That is the scariest part for me because most slabs dry from the top down. Therefore, it could be very wet inside, but the calcium chloride test would not reveal that.
Why does moisture below the surface matter? Because moisture vapor moves up - water in the ground or in the slab turns to vapor through the process of evaporation and moves up into the sky to form clouds and then rains down so the cycle can start over again. So, if the slab is damp below the surface, moisture will eventually work its way up - affecting the floor covering and the adhesive.
This test involves drilling holes to measure moisture inside the slab - a more accurate way of predicting what will happen in the future. Denise Padgett, Sales & Marketing Manager for Wagner Electronics, a manufacturer of handheld moisture measurement devices, explains, “Unlike calcium chloride testing, relative humidity probes are less sensitive to fluctuations in ambient air humidity and temperature above the slab.” Kanare agreed, saying “RH testing gives a much more useful picture of the actual moisture condition within the concrete regardless of mix, aggregate types, floor thickness, or surface conditions.” I’ve noticed that limits for RH tests are starting to show up in manufacturer’s installation manuals, and Padgett agreed, saying, “Many areas within the industry are moving towards RH testing.”
How can you get trained on concrete moisture testing? The Institute of Inspection, Cleaning and Restoration Certification (IICRC) has developed “Introduction to Substrate/Subfloor Inspections (ISSI),” a three-day course including a 160-question exam. I would highly recommend this course to anyone who is serious about upgrading their level of professionalism regarding moisture testing, including flooring contractors, installers, inspectors and water damage restoration specialists. As more floors continue to fail because of moisture, and more data points to the best ways to test for moisture, it’s imperative the industry learn these methods and put them to use on every job.