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
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
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.
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