Calcium Chloride Testing by the Book
During the seminars I conduct -- whether my audience consists of installers, architects or salespeople -- I speak about the importance of testing all concrete before floor coverings are installed, regardless of its age or grade level. My very simple rule is: If it's concrete, you have to test it!
Many times, someone comes up to me after my presentation and says, "I just learned that I've been testing the wrong way." Our industry has sponsored a lot of education about testing and, thankfully, more concrete is being tested all the time. But too often, the tests are being performed incorrectly.
George Donnelly, a professional inspector from California who does a lot of moisture testing, confirmed this. "I regularly talk to persons that have either performed tests without properly preparing test sites, created too few test sites, tested in buildings that are not properly acclimated or not recorded pertinent data to place in job files," he says.
Well, if you intend to test "by the book," then you better be sure to get the book! "Anyone who wants to be involved with moisture testing," Donnelly explains, "owes it to themselves and their clients to invest in three documents from ASTM International -- ASTM F710 (Preparing Concrete Floors to Receive Resilient Flooring), ASTM F1869 (the Calcium Chloride Test) and ASTM F2170 (Internal Relative Humidity test)."
I agree 100 percent and would add the Floor Covering Industry White Paper to the list of required reading as well. However, Donnelly notes, "too many people are unaware that the standards even exist." That's sad, but true.
Use of moisture meters or a sheet of plastic as testing methods should not be relied upon to make a conclusive decision as to whether the concrete is suitable for a floor covering installation. The only accepted methods are ASTM F1869 and/or F2170. The test used in the United States for the past 30 years is the calcium chloride test, formerly called the Rubber Manufacturers of America (RMA) test and now known as ASTM F1869, Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.
ASTM F1869 takes four days to complete. The concrete is cleaned and left open for one day, and then a dish of salt (calcium chloride) is placed on the slab and sealed under a plastic dome for three days.
If you've ever tried to put salt on your food on a humid day, you know that the grains tend to clump together because salt absorbs moisture from the air. The calcium chloride test works on the same principle. The calcium chloride contained in the covered dish absorbs water vapor that comes out of the concrete and thus gains weight.
Using a specific formula, this weight gain is expressed as pounds of water vapor per 1,000 square feet per 24 hours (lbs/1,000 ft2/24h), or just "pounds." The limit for floor coverings (including carpet) is either 3 lbs. or 5 lbs., depending on the product.
Sounds like a simple test, right? It is, but an expert in the field recently told me that nearly 60 percent of them are not performed correctly. Here are four reasons why:
Not enough tests. ASTM F1869 says to test three test locations for areas up to 1,000 square feet and one additional test for each 1,000 square feet or fraction thereof.* This means a 5,000-square-foot floor should have seven tests. Why? Each ready concrete mix truck holds about 800-square feet of concrete, so you catch most of the truckloads this way.
Job site not ready. The test site should be at the same temperature and humidity expected during normal use. If this is not possible, then the temperature should be 65º to 85º Fahrenheit and 45 to 55 percent relative humidity.* If the heat or air conditioning system (HVAC) is not running, don't even bother doing the test. Why? The concrete will be in equilibrium with the air and there will be less vapor movement out of the slab than there is when the HVAC is on.
No waiting after cleaning. Expose a minimum area of 20 inches by 20 inches to [these] conditions for a minimum period of 24 hours prior to starting each test.* Therefore, clean a 20-inch square of concrete (by sanding or grinding), leave it undisturbed for 24 hours and then place the test kit. Even on new concrete, this is very important. Why? Waiting allows any surface moisture to evaporate so you are testing only what is coming out of the concrete, and thus avoiding a false high reading.
The question of who should perform concrete testing was answered by the floor covering industry when virtually every industry association combined their efforts to create the Floor Covering Industry White Paper Position Statement on Moisture Emission Testing. The meat of this document states: It is our recommendation that concrete moisture vapor emission testing be performed by qualified independent agencies.**
At this juncture, there is a shortage of "qualified independent agencies" to do this work, but training programs such as the IICRC Substrate/Subfloor Inspector certification program will be in place soon to address this need. In the meantime, you need to know how to perform the tests and have the courage to "just say no" to installing floors over concrete that is not ready.
This is the bottom line. If you fail to test, or proceed with a job when you know the readings are too high, you are on your own. And if that floor goes bad, you'll have to deal with a very unhappy customer and a very expensive replacement.