Source: Concrete Construction Magazine
Publication date: September 1, 2007
By Howard Kanare
A major change is taking place in the way that the floor covering industry measures moisture in concrete floors. This change affects concrete floor contractors, general contractors, construction managers, owners, architects, and floor covering installers. Just as the concrete floor construction industry made the shift in flatness tolerances from straight-edge to the more appropriate statistically based FF/FL system, now the floor covering industry faces a major shift from measuring moisture vapor emission rate (MVER) to measuring relative humidity (RH).
The anhydrous calcium chloride test for moisture emission rate was developed in the 1940s as a qualitative evaluation of floor moisture condition. Without any documented scientific basis, it became a quantitative test in the 1960s. Now, nearly a half million MVER tests are performed each year in the United States. In the past decade, we have learned that the test can be unreliable; capable of producing high false high and low results; and dependent on ambient temperature and humidity, water-cement ratio, use of a lightweight aggregate, the presence of curing compound, how hard a floor was troweled, and how the test site is prepared.
Over the past 10 years, CTLGroup has investigated the performance of the MVER test method in the field and in the lab, and we have found that it suffers from several serious deficiencies:
RH for floor moisture measurement is not new — it was first used to measure moisture in concrete floors as part of PCA-applied research programs in our laboratories beginning in the 1950s. RH instruments can be independently calibrated directly traceable to national standards. There are a variety of commercially available RH instruments specifically for measuring moisture in concrete. Although RH instruments cost more than a calcium chloride MVER kit, large savings in testing time and labor are making RH the method of choice. More importantly, RH testing gives a much more useful picture of the actual moisture condition within the concrete regardless of the mix, aggregate types, floor thickness, or surface conditions. Properly conducted RH testing can prevent premature flooring installation that can lead to costly repairs and litigation.
RH has been the preferred method for assessing concrete floor moisture conditions in a number of countries for many years. Limits for installation range from 60% RH for direct glue-down wood parquet to 90% RH for some vinyl tile products. Flooring manufacturers in the United States must establish realistic RH limits for acceptable performance of their products, through rigorous scientific testing, taking into account the various components of their systems, such as patching/leveling compounds, primer, adhesive, and floor coverings. I anticipate that manufacturers eventually will develop “tiered systems” that will allow design professionals and contractors to select flooring products for various moisture levels, to produce enduring, successful outcomes.
Howard Kanare is a senior principal scientist at Construction Technology Laboratories (CTL)Group, Skokie, ILL., 847-522-2285 or email@example.com