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The hygrometer probe test is the most accurate of the concrete moisture testing methods. It measures the internal relative humidity of a concrete slab (40 percent of the slab’s thickness) at the apex of the concrete’s drying curve. By taking the measurement at 40 percent of the slab’s thickness, it is easier to predict the effect moisture will have on the material placed over the concrete surface. To look at the process we must examine the steps involved, which are as follows:
These are some of the different types of internal relative humidity moisture testing devices available (Photo 1). Each has the ability to give accurate internal relative humidity readings. The key to achieving these accurate readings is the proper use of this equipment.

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After the sleeve has been in place for 72 hours, the hole is acclimated and ready for testing. Remove the protective cap on the sleeve and place the probe into the sleeve (Photo 6). Allow the probe to acclimate to the slab temperature to achieve the optimum reading this can take as long as one hour depending upon the temperature of the probes and the slab. When completed, be sure to record all the data. This includes the slab temperature, the ambient room temperature, and ambient relative humidity, the time elapsed from the start to the first test, the date, and the time.
By following these simple rules, you can get a very accurate picture of the internal moisture of a slab and how it will receive new moisture sensitive flooring.

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