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Page 32 of 39

COATINGSPRO SURFACE PREP 2017 33 2. Relative humidity (R H). A lso called the in situ RH testing, this test involves drilling a hole and placing an RH probe to a depth of 40 percent of the overall thickness of a concrete slab that is dr y ing from one side. Independent research has clearly demonstrated the importance of taking RH measurements at the 40 percent depth. T his depth provides the best indication of the moisture that the coating w ill "see" once the slab is sealed. Dictated by ASTM F2170: Standard Test Method for Determining Relative Humidit y in Concrete Floor Slabs Using in situ Probes, this test assures the fastest, most accurate readings of real-time moisture conditions w ithin the slab. Common Coatings for Concrete Once the moisture of the concrete has been determined, the next step w ill be to apply the high-performance coating. T his is another area where some insight is necessar y. Choosing the right — or wrong — coating for the project can make a big difference. 1. Epoxies. T he most w idely used epoxies are solvent- or water-borne w ith a high moisture content. Epoxies adhere well to concrete after the surface has been etched, as pores in the concrete are necessar y to enable the epox y to form a mechanical bond. W hen applied correctly, epoxies help improve the f loor's chemical resistance and can also help to provide a non-skid surface. 2. Poly urethanes. Poly urethane resins offer the most resistance to moisture, mold, and high humidity. T hese coatings are chemical- and shrinkage-resistant, have fast curing times, and are great for high-performance f loors. A dr y concrete surface is an absolute must if you want poly urethane coatings to adhere well; other- w ise, you could end up w ith ugly blistering and other moisture-related problems. 3. Acrylics. Acrylics can differ in their chemical make-up. ey vary from rubbery, elastic-like structures to hard solids, as well as thick and sticky liquids. Although they perform well in general, they tend to be less chemically Once the concrete's moisture has been determined, it's time to apply the high-performance coating. When applied correctly, epoxies, for example, can help improve the floor's chemical resistance and provide a non-skid surface. Moisture Tolerances continued on page 38

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