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
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:
Test Method for Determining Relative Humidity in Concrete Floor
in situ Probes ) measures at a 40 percent depth in the