If you don’t use a grinder to do a Calcium Chloride test, you are not doing the test correctly and your results are invalid!


A perfectly prepared moisture test site. The slab is ground clean in a 20”x20” area, the calcium chloride kit is placed and a relative humidity test site is to the left of the calcium chloride dome.



This month marks the tenth anniversary of the publication of the “Floor Covering Industry White Paper Position Statement on Moisture Emission Testing,” published by ten different trade organizations in October 2001.  Despite that excellent document and all that has been written in trade magazines, manufacturer’s instructions, and ASTM, I find it puzzling that many in our industry still are not placing a priority on concrete moisture testing. I would have expected to see it be a more widespread practice by now, especially with millions of dollars in moisture-related failures still happening every year.  While I agree wholeheartedly with the summation of the White Paper that says, “It is therefore our recommendation that concrete moisture vapor emission testing be performed by qualified independent agencies,” I also recommend that flooring installers and project managers become aware of the different test methods and how to do them correctly. When and where should a concrete floor be tested?  Everywhere and always! The industry standard, ASTM F 710, says it all, “All concrete slabs be tested for moisture, regardless of age or grade level,*” and most manufacturers say the same.

Do not use qualitative methods such as moisture meters, plastic sheets or a visual inspection to reach a conclusion that a moisture condition exists, or that a slab is “dry.” These outdated methods are not accepted as a way to determine if a slab is ready to receive a floor. The two qualitative methods that are accepted by the floor covering industry are the Relative Humidity method and the Calcium Chloride test.

Preparing a Relative Humidity (RH) test site; RH testing is gaining in popularity as a more accurate and more easily repeatable method. Photo courtesy of Wagner Electronics.

Recent Changes 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,” is well known in North America and was originally published in the 1950s by the Rubber Manufacturer’s Association (RMA). It measures the MVER from the top ¾” or so of the concrete.

Most floor covering limits for  MVER are 3 to 8 pounds per 1,000 square feet per 24 hours (lbs/1,000 ft2/24h), depending on the product and/or the adhesive. Unfortunately the test is often done incorrectly, which makes a lot of the testing that is done invalid. For example, the temperature requirement is often ignored.  “The test site shall be at the same temperature and humidity expected during normal use. If this is not possible, then the test conditions shall be 75 +/-10°F (18.3°C - 29.4°C) and 50 +/-10 % relative humidity. Maintain these conditions 48 hours prior to, and during testing.+”  If you can’t do the test under these conditions, don’t bother doing the test because this method is very sensitive to ambient conditions and the results are worthless otherwise.

The other most common mistake doing the Calcium Chloride test is failure to prepare the concrete correctly.  Because of this, ASTM F 1869 has recently been revised to clarify this procedure.  The concrete must be cleaned with a grinder and the test must not be done over coatings or patching compounds – it’s designed for “determination of the rate of moisture vapor emitted from…bare concrete floors**.”  It also says not to test over patching or leveling compounds, lightweight concrete, gypsum underlayment, moisture mitigation systems or other coatings.  It’s for bare naked concrete only.

To properly clean the concrete, “Remove floor coverings or coatings. Lightly grind an area 20 by 20 in. (50 x 50 cm) to produce a surface profile equal to ICRI CSP-I to CSP-2. Grinding should remove a thin layer of the finished concrete but not expose coarse aggregate, unless the surface had been abrasively treated previously**.”  CSP is the Concrete Surface Profile established by the International Concrete Repair Institute (ICRI).   A light grinding should produce a texture similar to course sandpaper.  It is not enough to scrape, sand or wire brush the surface.  It must be cleaned by grinding.

If a floor covering or coating is present, there is a 24-hour waiting period after cleaning before the kits can be placed. Otherwise, “Concrete floors that have not had floor coverings or coatings within 30 days prior to testing can be ground and tested without this waiting period, provided the [temperature and humidity] conditions have been met. **.” Since some coatings such as curing compounds may not be visible, I prefer to always wait 24 hours, but if you are sure you are dealing with uncoated concrete you can grind and place the kits right away.

This vinyl plank floor was installed on concrete that had not been tested and quickly failed, and failed badly due to moisture.

Relative Humidity Testing



While the F 1869 Calcium Chloride test, done correctly, is a good test for surface moisture, it does not measure “deep down” moisture. Since most concrete dries from the top down, this is a serious limitation because the concrete could be dry on top and very damp inside.  The F 1869 test won’t “see” that and internal moisture will move to the top after a floor is installed, even if the F 1869 test results are passable before the floor is installed.  That’s a scary thought.  

Relative Humidity (RH) testing measures “deep down, has been used in Europe for decades, and is now gaining some popularity in North America.  It is known here as “ASTM F 2170, Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes.” With this method, holes are drilled to 40% of the slab thickness – usually about two inches down.  The hole is vacuumed clean and a plastic sleeve is inserted.  After a recommended waiting time, a relative humidity probe is used to determine the equilibrium relative humidity in the cavity at the bottom of the hole.  Usually a reading of 70-80% is acceptable.  RH tests are more accurate than Calcium Chloride, take less time and are easily repeated days, weeks or even months after the original test.  This test is thought of as being the best way to the future as far as moisture rising to the surface of the concrete.  This is truly the latest technology for moisture testing and is very quickly being recognized by flooring manufacturers throughout the world.  Another RH method, ASTM F 2420, “The Hood Method” measures RH on the surface of the concrete slab and is a good alternative when drilling is not an option.

Quantitative moisture test methods like ASTM F 2170 are preferred to old methods like a plastic sheet on the floor because they give a numerical test result. Photo courtesy of Delmhorst.

Which Test?



I am not alone in recommending both Calcium Chloride and RH tests be done together because they measure different things. If F 2170 results are low and the F 1869 test is high, that may mean the slab is dry, but the surface became wet because of a flood or other source of moisture. So, dry out the surface and you are good to go. However, if the results are opposite and the F 1869 test is low and the F 2170 test is high, that indicates that the slab is drying from the top down, but there is still a lot of moisture inside waiting to come up.

Many people use a combination of moisture meters, calcium chloride and relative humidity testing to determine if the concrete is ready for a floor covering installation, and these methods are also used to troubleshoot a floor that has failed because of moisture.  Regardless of which test method is used, it is imperative that the test protocol be followed to the letter.  

How to Learn Testing



There are two excellent certifications I’d recommend for people who want to learn more about concrete and how to test. The Institute of Inspection, Cleaning and Restoration Certification (IICRC) offers “Introduction to Substrate/Subfloor Inspection (ISSI)”, a two-day course. Also, International Concrete Repair Institute (ICRI) offers a two day Moisture Testing Certification that includes a “hands on” portion for moisture testing technicians.

Thank You



This column marks the start of my 9th year writing “Let’s Talk Resilient” for FCI, and a lot has happened since my first column in October, 2003. I’d like to thank John Moore, FCI Editor for being great to work for and also thank you, my readers, for your many positive comments, great questions and generous compliments over the years.References and resourcesListing of IICRC Schools offering ISSI at www.IICRC.org/schoolsICRI Concrete Sab Moisture Testing Program www.icri.org

# Floor Covering Industry White Paper Position Statement on Moisture Emission Testing, (available at www.FlooringAnswers.com)

* ASTM F 710 Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring (ASTM International, www.astm.org).

+ ASTM F 1869 Standard Test Method for Measuring Moisture Vapor Emission Rate (MVER) of Concrete Subfloor Using Anhydrous Calcium Chloride (ASTM International, www.astm.org).

** ASTM F 1869, “Standard Test Method for Measuring Moisture Vapor Emission Rate (MVER) of Concrete Subfloor Using Anhydrous Calcium Chloride,” (ASTM International, www.astm.org)