For decades, calcium chloride (CaCl) testing has been used to determine the suitable moisture content of poured concrete slabs when applying resilient floor coverings. The standard for performing the CaCl test has seen many changes over the years. The initial testing only called for determining qualitative results but it soon became apparent that a more quantitative approach that provided more than just someone’s opinion was needed for threshold decisions. Various changes were proposed but the CaCl method continued to be unwieldy, uncertain in results and inefficient in terms of both time and materials. Clearly a more user-friendly, accurate means of determining concrete moisture would be welcomed by the entire resilient floor covering industry.
Since 2002, ASTM F2170 In Situ Relative Humidity (RH) testing has been replacing CaCl as the preferred method for concrete moisture determination. And in 2010 the ASTM committee changed the F1869 CaCl standard to specifically disallow CaCl testing for all lightweight aggregate concrete as results which had long been suspected as inadequate were finally confirmed. If RH testing using ASTM F2170 was not here to take its place, the entire industry certainly would have been thrown into turmoil. This recent decision clearly demonstrates the need for having an alternative to the antiquated F1869 CaCl testing standard.
Going as far back as the 1940s, CaCl testing has been used to determine the suitable moisture content of poured concrete slabs when applying resilient floor coverings. The standard for performing the CaCl test has seen many changes over the years but has remained problematic from a reliability and scientifically grounded standpoint. As continued testing has been done, suspicions about the reliability of CaCl testing was confirmed as the test method was proven to provide inadequate results. So in 2010, the ASTM F1869 standard for using CaCl was changed to specifically disallow CaCl testing for all lightweight aggregate concrete (1).
What then is the alternative? In situ RH testing, according to ASTM F2170, has for a number of years now been replacing CaCl as the preferred method for concrete moisture determination. Not only are RH results more consistently reliable, RH testing has also proven to be cost-efficient, user-friendly and more appropriate to the resilient floor covering industry.
The first known published information on CaCl testing for concrete was by Armstrong in the 1940s as a “go or no go” type of test, according to Howard Kanare of CTLGroup (2). It was used with no numerical assessment resulting from the test. There is also no record of the science behind the decision to use anhydrous CaCl instead of another desiccant. Regardless, it went into use as a method of testing concrete readiness for linoleum application.
When Kentile began to sell CaCl test kits in the 1960s, measuring the weight of the salt before and after exposure to vapor emissions from concrete became the recommended practice. This method is also known as a moisture vapor emission rate (MVER) test. But again, scientific record at that time did not support the target range of numbers given with the test as being suitable for flooring installation conditions. And inherent to CaCl testing, uncertainties occurred due to varying ambient environmental conditions, varying concrete mixtures, and various admixtures.
In the 1990s, Kanare’s team at CTLGroup performed their own testing to try to determine the accuracy of CaCl as a test method. Their testing showed several problems with the ASTM F1869 standard for CaCl testing (3). The most serious problem with the CaCl test is that at the higher end of moisture conditions, where there is the most danger of floor covering failures, CaCl testing following the ASTM F1869 standard can underestimate the true moisture condition. A much less serious phenomenon is the overestimation of the moisture conditions in very old slabs that are not actually emitting any net moisture vapor. Added to their findings was the observation that a CaCl test only measures the top ½ – ¾ inch of the slab, while typically higher concentrations of moisture reside deeper in the slab and migrate to the surface after applying a floor covering. The conclusion of their testing was that CaCl testing was fundamentally unreliable for predicting the performance of resilient floor coverings over concrete.
Also in the 1990s, Goran Hedenblad began researching the characteristics of concrete moisture through the Swedish Council of Research. Hedenblad performed experiments that identified moisture gradients in a slab from the exposed surface to deeper into a slab; further testing indicated that after a slab was covered, the moisture re-distributed to equalize to a constant moisture concentration throughout the slab. Final indications showed that after the slab was covered, the surface presented a higher moisture concentration to the floor covering after this equalization process. Hedenblad’s research provided the foundation for what we now know more commonly as RH testing as outlined by the ASTM F2170 standard (5). With RH testing, a probe is installed (“in situ”) at 40% of the concrete slab’s thickness to measure the moisture conditions in the concrete; these same conditions will ultimately be seen at the surface once covered by a floor or other vapor retarding system. Clearly, RH testing provides the best answer to the moisture level that will eventually be exposed to a floor covering system.
According to an article written in 2007 by Claudia Lezell, past president of the Flooring Technology Institute, “The studies cited [in the article] help support that the critical number, as far as the installation of floor covering goes, is internal RH. We are also being shown that the MVER might not be giving us all of the information we need to know when the concrete redistributes moisture after being covered with a low-permeance floor covering.” (6) Further studies also concluded that the MVER testing made it difficult to predict drying time accurately for the purpose of applying floor coverings (7).
For the flooring industry, this combination of MVER uncertainty and new research has created a trend towards RH testing, with many manufacturers now specifying RH testing as the preferred method to determine concrete slab moisture conditions. Indeed, the US is the only country to ever adopt CaCl to measure concrete moisture and cutting edge companies are now consistently moving away from CaCl testing and towards the global industry standard for RH testing provided by the ASTM F2170 standard.
Future of the Industry
It is increasingly obvious that CaCl is being replaced and RH testing will be the dominant moisture testing method in the very near future. CaCl testing is increasingly proving to be inefficient and somewhat clumsy as a test method for the concrete industry. Because each test naturally “destroys” the salt mixture as it absorbs moisture when a new test is required, the old test kit must be discarded, and a complete new kit must be employed to obtain each additional measurement.
RH testing, however, has been increasingly adopted as an accurate and cost-effective means of testing concrete moisture conditions. “The RH tests can provide us with information before, during and after the drying process, which can only help us to make a better determination if the concrete is dry and ready to receive floor covering of any type,” stated Lezell (8). Progress made in the technology of RH testing over the past five years has only made the process simpler and more cost-effective to use.
With CaCl testing falling into disrepute and the recent change to ASTM F1869 that disallows it as a test method for lightweight concrete, it raises the question of whether the same findings will eventually be applied to normal weight concrete applications as well. The alternate RH testing appears to be the straw to break the back of antiquated and questionable CaCl testing.
The standard for moisture testing for resilient floor coverings over concrete has changed, and this change of the ASTM F1869 standard reflects the findings of recent studies in lightweight concrete. CaCl testing is no long acceptable for lightweight concrete. Instead, RH testing provides an accurate method of testing moisture content within a concrete slab to obtain reliable results and make properly informed decisions when applying flooring over concrete. Understanding the changes, and the science behind RH testing and ASTM F2170 will help installers, developers and contractors specify the testing method best suited to give reliable, actionable results for the resilient flooring industry.
RH testing to the rescue!
2, 3. Howard Kanare, “Calcium Chloride Proven to Give False Readings” http://www.wagnermeters.com/rh4.php
4. Hedenblad, G., “Drying on Construction Water in Concrete,” T9:1997, Swedish Council for Building Research, 1997. (Available from Svensk Byggtjanst, Stockholm.)
6. Claudia Lezell, “Concrete: When Do You Know It’s Dry?”, 2007 http://www.randrmagonline.com/Articles/Feature_Article/BNP_GUID_9-5-2006_A_10000000000000155900
7. Bruce A. Suprenant and Ward R. Malisch, “Are Your Slabs Dry Enough for Floor Coverings?” 1998 http://www.wwwf.advancedmoisturecontrol.com/Resources/Articles/article%20by%20suprenant1.pdf
8. Claudia Lezell, “Concrete: When Do You Know It’s Dry?”, 2007 http://www.randrmagonline.com/Articles/Feature_Article/BNP_GUID_9-5-2006_A_10000000000000155900