Recent changes to the ASTM F1869 standard for using calcium chloride have made the message clear: calcium chloride is not acceptable when it comes to testing moisture on all lightweight aggregate concrete (1). In spite of its history in the industry, moisture testing with calcium chloride for lightweight concrete and particularly in the application of resilient floor coverings was shown to provide inadequate results (2) and ASTM has reflected the latest research in their 2010 industry standards, leaving RH testing as the preferred method.

Calcium chloride testing was originally implemented over 50 years ago as a qualitative, rather than a quantitative, test for measuring moisture in concrete, and was used as a “go or no go” indicator of slab moisture conditions, according to Howard Kanare of CTLGroup (2). With unclear reasoning, however, it became accepted as a quantitative standard and has stayed in use since the 1940s.

The calcium chloride test also has some practical drawbacks. For example, because each test naturally “destroys” the salt mixture as it adsorbs 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.

What then is the alternative? For the flooring industry, the combination of calcium chloride’s uncertainty and new research has created a trend towards in situ Relative Humidity (RH) testing, begun largely on the foundation of research done by Göran Hedenblad of Sweden in the 1990s (3). Cutting edge companies are now consistently moving away from calcium chloride testing and towards the more globally-accepted industry method of in situ RH testing as outlined by the ASTM F2170 standard and related standards outside the US. Not only are RH results more consistently reliable, RH testing has also been shown to be more cost efficient, user friendly and more appropriate to the resilient floor covering industry.

“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,” pointed out Claudia Lezell, past president of the Flooring Technology Institute (4).  And 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.

RH testing provides an accurate method of testing moisture within a concrete slab to obtain reliable results and make properly informed decisions when applying flooring over lightweight concrete. Understanding the changes, and the science behind RH testing and ASTM F2170 will help manufacturers, installers, developers and contractors alike specify the testing method best suited to give reliable, actionable results for the resilient flooring industry.

For more information, visit www.rhspec.com.

1.     http://www.astm.org/Standards/F1869.htm

2  Howard Kanare, “Calcium Chloride Shown to Give False Readings” https://www.wagnermeters.com/relative-humidity-testing-video/calcium-chloride-false-readings/

3. Hedenblad, G., “Drying on Construction Water in Concrete,” T9:1997,

Swedish Council for Building Research, 1997. (Available from Svensk

Byggtjanst, Stockholm.)

4. 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