Concrete Moisture Problems: Causes and Detection
CausesBad concrete or bad adhesive? This is a lively debate to explain why there are so many moisture related-failures today. Yes, concrete and adhesives have changed over the years, but I am not going to debate this question here. With or without these changes, two terms explain where many of the problems are coming from: fast track construction and adaptive re-use.
Fast Track ConstructionLet's face it; they build buildings a lot faster than they used to. Flooring is often installed over concrete that is not yet dry or before the Heating/Ventilation/Air Conditioning System (HVAC) is operational, which can lead to problems later when the excess water vapor in the concrete is drawn upward by the dry conditioned air.
You may have heard the statement "Concrete cures in 28 days, so it is ready for flooring at that time." True and not true. New concrete slabs shall be properly cured and dried before installation of resilient flooring. Drying time before slabs are ready for moisture testing will vary depending on atmospheric conditions and mix design. Notice that this specification uses "curing" and "drying" in the same sentence - they are two different terms. The three main ingredients of concrete - water, aggregate (rocks and sand), and cement (the gray powder) - go through a chemical curing process that in the average four-inch concrete slab takes about 28 days. But, that does not mean the concrete is dry at that point. After curing, the excess water evaporates out. So, "cured" does not mean "dry."
The use of curing compounds is another concern. Initially, the water in concrete needs to be kept in so the chemical reaction can occur. The old way of curing concrete used wet burlap to keep the new concrete surface wet for seven days. After that, the concrete began to dry immediately with nothing on the surface to block the evaporation. Unfortunately, this method has been virtually replaced by liquid curing compounds that trap the moisture, despite the industry standard that states, "Concrete floors to receive resilient flooring shall be free of sealers, coatings, finishes, dirt, curing compounds, or other substances which may affect the rate of moisture dissipation from the concrete or the adhesion of resilient flooring to the concrete." On renovation jobs, that means treating adhesive residue properly. Depending on what type of residue, either completely remove it or scrape it and cover it with the proper patching compound, or risk what happened under the six-year -old floor in Photo 2 - cutback residue plus acrylic adhesive plus a moisture problem - a soupy, smelly mess. On new slabs, this means curing compounds must be removed. I feel that if curing compounds are used, they should be removed soon after the concrete is placed, to open up the pores of the concrete and help it dry faster.
Another statement that gets people in trouble is "You only have to worry about moisture problems in slabs that are on grade or below grade." Again, true and not true. Many problems occur in slabs on or below grade because ground water vapor passes thorough concrete and softens the adhesive. This is often diagnosed as "hydrostatic pressure," which is the wrong term. Hydrostatic pressure occurs only below grade (never on grade) where there is actual water in contact with the concrete (such as a basement in a building that has bad drainage outside the foundation. However, much more common than hydrostatic problems are ground water problems. If a slab does not have a vapor barrier beneath it, ground water vapor passes through the concrete freely. So, concrete in contact with the earth is definitely an issue, so knowing if a vapor barrier is present is a good way of predicting if a moisture problem may occur in the future.
However, don't make the mistake of assuming that everything from the second floor up will be problem free. Some of the worst moisture failures are above grade because "lightweight concrete, floors containing lightweight aggregate or excess water, and those that are allowed to dry from only one side, such as concrete on metal deck construction, may need a much longer drying time." In order to get the concrete up to the higher floors, it is pumped, as opposed to days gone by where it was hauled up in giant buckets using cranes and "standard mix" concrete. The pumpable, lightweight concrete of today has more water in it so it takes longer to dry, which is why above grade slabs are also suspect.
I have often been told that there would never be a moisture problem in a desert environment. Tell that to the thousands of building owners in the Southwest and California who have had moisture related failures - they have as many or more problems than the rest of the nation! You can see an example in Photo 3, which was taken in Phoenix recently. Why are there still moisture problems in the desert? Vapor barriers are left out of the buildings even though there is still groundwater (and often a high water table) in the desert, floors are installed too soon after the concrete is placed, extra water is added to the concrete trucks to keep the mix "alive" in the desert heat, and so on. Don't assume because you are in a dry climate that you are immune to moisture related failures.
Adaptive Re-UseI've often heard "We don't have to worry about moisture problems in an older building." Wrong! More and more often, spaces that were designed for a particular use such as a warehouse, are being are changed to a different use such as shops or offices. This is known as "adaptive re-use." There are a lot of moisture problems in these types of buildings, such as one of the worst moisture problems I have seen in recent years. A 30-year old building that was originally a warehouse was converted to a furniture store. There was no vapor barrier under the concrete because it's not necessary for a slab that will not be covered. For 30 years, ground water vapor moved through that slab unnoticed, until the floor was covered with sheet vinyl, which sealed the surface. The adhesive turned to mush and a very good heat welded installation was ruined. So, remember, all concrete slabs must be tested for moisture regardless of age or grade level! Similarly, the assumption "There was no moisture problem with the old floor so we don't have to worry about the new floor" has lead to many a failure. If the old floor was 9x 9 VAT or carpet, for example, minor vapor emissions may have escaped unnoticed. Remove or cover that floor with larger tiles, vinyl back carpet or sheet vinyl and now the vapor has nowhere to go but into the adhesive.
Moisture TestingHow can we prevent all of these problems like the curling tile in Photo 4? Well, the first defense is detection - knowing what you've got every time you start a job over concrete. Make sure that testing is done and done correctly so that if there is a problem you catch it before installing the floor covering.
I've been told "It didn't look (or smell or feel) wet," "I used a moisture meter," "We've never had a moisture problem so we don't test." Well, welcome to the 21st century everyone! The stakes are higher because of the high cost of repairing moisture related failures, not to mention the liabilities of mold and other issues than can affect a building when there is a concrete moisture problem. it's time to make testing a part of your routine. Our industry has done a good deal of education around the issue of testing, and in my travels I am finding more and more floors being tested all the time. That is good news. But I am concerned that the tests are not being done correctly or under the right conditions.
The test being used in the U.S. for over 30 years is known at the calcium chloride test. It was called the Rubber Manufacturers of America (RMA) test, but is now ASTM F-1869, Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride. Using a kit such as the ones shown in Photo 5, a dish of salt (calcium chloride) is placed under a sealed plastic dome for three days (60-72 hours). It absorbs the water vapor that comes out of the concrete and gains weight. Using a formula, this weight gain is expressed as pounds of water vapor per one thousand square feet per 24 hours (lbs/1000 ft2/24h), or just "pounds". Most of today's resilient flooring and carpet needs to be installed under 3 pounds or under 5 pounds, 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 done correctly. Here are four major areas where a lot of tests go wrong: o ASTM F 1869 says to test three test locations for areas up to 1000 square feet and one additional test for each 1000 square feet or fraction thereof2. That means a 5000 square foot floor should have seven tests. Each ready mix truck holds about 500 square feet of concrete, so the frequency of tests is an important way to catch several different batches of concrete. o 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 65-85 degrees Fahrenheit and 45%-55% relative humidity2 If the HVAC is not running or if there are no doors and windows, don't even bother doing the test. 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. o The actual test area shall be clean and free of all foreign substances. All residual adhesives, curing compounds, sealers, paints, floor coverings, etc shall be removed. In other words, on new or old slabs, we need to test bare concrete. o Expose a minimum area of 20 in. x 20 in. to [these] conditions for a minimum period of 24 hours prior to starting each test 2. Clean a 20-inch square of concrete (usually by sanding or grinding), leave it for 24 hours, and then place the kit. Even on new concrete, this is important.
A new method, ASTM F2170-02 Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes, involves drilling a hole in the concrete to determine the relative humidity inside the slab - moisture that may work its way to the top eventually. This method, which has been used for some time in Europe, is thought by some experts to be a more accurate predictor of future moisture movement, since studies have shown that the Calcium Chloride test only measures moisture emitting from the top one inch or so. This method is also much easier to repeat - once you have the hole drilled you can go back and easily get another reading without the waiting time involved in a Calcium Chloride test. 75 percent relative humidity is an accepted limit for most floor coverings using this method. Check with the manufacturer of the flooring to see what limits they recommend for either of these two tests.
Other methods such as moisture meters, the rubber mat test, and taping a plastic sheet to the floor, may, at best identify an area that may need some further testing. Then again, they could also falsely identify an area as "dry". These methods should not be used to make the decision to "go or no go" with a new floor. Your best bet for moisture testing is either the ASTM F 1869 or F2170 methods mentioned above. Or both.
Finally, no conversation about concrete testing is complete without talking about the test everyone forgets about, pH. Concrete floors shall be tested for pH prior to the installation of resilient flooring. To test for pH at the surface of a concrete slab, use wide range pH paper, its associated pH chart, and distilled or deionized water.1 This is a simple test that only takes a few minutes using a kit like the one shown in Photo 6. If the pH results are more than 10, this is out of the range of most floor covering adhesives, and may indicate excess vapor emission or other problems on the surface of the concrete. On the other side, pH less than 7 may indicate some type of acid or other residue is on the floor. So, if you are in the 7-10 range, do the job. If not, don't without doing some additional analysis or at least making a phone call to the floor covering manufacturer.
Who Should Do It?The question of who should do 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 is the following statement: It is unreasonable to expect a general contractor, concrete contractor or a flooring installer to have sufficient expertise to anticipate and ask the proper questions for evaluation of potential concrete/flooring problems. Another complicating factor is that each has a vested interest on the testing and/or performance outcome of the installation. Flooring contractors should be made aware of test results, as all flooring manufacturers have placed upward tolerable limits of moisture vapor emission for the installation of their products, most have also recognized that adhesives will cure within a moderate range of pH. However, flooring contractors' expertise should, by requirement, be limited to flooring materials and their installation. Changes in construction materials and practices should not lead to a mandatory in depth expertise of all the disciplines mentioned above. It is therefore our recommendation that concrete moisture vapor emission testing be performed by qualified independent agencies.3
At this point in time there is a shortage of "qualified independent agencies" to do this work but hopefully efforts such as the IICRC Inspector training and certification program will be in place to remedy this in the next few years. In the mean time, it pays for floor covering professionals to not only know how to do the testing and do it right. , but to have the courage to "Just say no" to installing floors over concrete that is not ready! That is the bottom line. If you fail to test or go ahead 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 a very unhappy customer and a very expensive replacement.
FOOTNOTE: 1 Adapted, with permission, from ASTM F 710-98, Standard Practice for Preparing Concrete Floors To Receive Resilient Flooring, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. Complete copies of these standards may be purchased from ASTM, Phone (610) 832-9585, fax: 610-832-9555, e-mail firstname.lastname@example.org, website www.astm.org
2 Adapted, with permission, from ASTM F 1869-01, Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. Complete copies of these standards may be purchased from ASTM, phone (610) 832-9585, fax: 610-832-9555, e-mail email@example.com, website www.astm.org.
3 Floor Covering Industry White Paper Position Statement on Moisture Emission Testing available from WFCA 2211 East Howell Avenue Anaheim, CA. 92806 USA (800) 624-6880 Fax: (714) 978-6066 or at www.wfca.org.