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32 SURFACE PREP 2017 COATINGSPROMAG.COM Do I Need to Pay Attention to Moisture Tolerances? By Jason Spangler, Product Sales Manager at Wagner Meters Photos Courtesy of Wagner Meters P ay ing attention to excess moisture in your concrete f loor slab is crucial to a successful coating application. Coating manufactur- ers generally specif y moisture tolerances that indicate how moisture in the concrete w ill affect the coating after it's applied, and it's important to adhere to these. T hat's because too much moisture in your concrete can cause a coating failure when it does not adhere properly. Knowing the moisture condition of the concrete before starting work on a concrete project is a necessary first step in a successful coating application. Surface Moisture: Not the Whole Story Measuring the moisture at the surface of the concrete does only just that — gives you an indication of the amount of moisture that's present in the first ¾" (1.9 cm) of the slab. You have to go deeper to get the full stor y of the slab that you' ll be working on. Here are two of the most common methods of moisture testing in concrete: 1. T he calcium chloride (CaCl) test. ASTM F1869 -16: Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subf loor Using Anhydrous Calcium Chloride is only conducted at the surface layer. It involves placing a dome over a clean section of concrete w ith a small dish of calcium chloride. T he 60 - to 72-hour test is used to calculate the moisture vapor emission rate (MVER) as the salt in the test kit absorbs moisture. T hough still allowed by many f looring manufacturers, this test has been scientifically proven to y ield results that cannot be relied upon for know ing the true moisture condition of the slab. The calcium chloride (CaCl) test (ASTM F1869-16: Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride ) evaluates the surface layer of the slab. The relative humidity (RH) test (Dictated by ASTM F2170: Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes ) measures at a 40 percent depth in the concrete. Surface Prep

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