RH test results varying

[CC Solutions]

Kind of Pat,
The ASTM says the probe must acclimate to the temperature of the concrete. The temperature at the 40% depth may vary from the surface temperature.

With the Wagner Rapid RH the sensor is left inside the concrete to acclimate. Your most accurate reading is the initial reading when inserting the reader.

With removable probes in sleeves, the sensor is in the probe and that sensor needs to acclimate to the concrete temperature which can take quite a long time. Many manufacturers recommend waiting an hour or more for each reading. Even then, think of when the slab is on the ground and the internal temperature is 67*F and you have an aluminum probe sticking up into the room atmosphere which has the heat on and blowing on that probe at 80*F. That heat can change the reading of that probe! Then the next time you read that probe maybe the heat is off, or the cooling is on. It has been my experience that I could get wild swings in my RH measurements using removable probes and leapfrogging from hole to hole, from day to day, or when the sun shines on a probe or it is shaded.