Moisture meters and concrete floor slabs

[ajk1]

Moisture meters are sometimes used to measure the surface wetness of concrete slabs before installing adhered flooring materials. This should not be a substitute for measuring the moisture content or relative humidity within the concrete slab. There are different ASTM tests for doing that. It is critical to measure the intermal moisture content or RH, not just the surface wetness of the slab, or flooring failures may occur.

Is there any information on:
a) how moisture meters work when used on concrete slab surfaces (do they electrically measure the surface electrical resistance or resistivity?);
b) to what depth are they measurng the moisture;
c) what their accuracy is when used in this manner;
d) is there any recognized Standard (such as ASTM) covering the use of moisture meters on concrete.

 

[EngineeringEric]

Sounds like you need to talk a meter rep. And there are ASTM Standards. Some of the meters/standards are not electronic and measure the moisture emissivity of the concrete (ie measure how much water is coming through the slab with water sensitive tablets) I cannot think of the standards or the actual products names as it has been too long since i used them. I will let you know once I remember.

 

[oldestguy]

In addition, you may wish to check out how to measure moisture tension (suction) as well salt content near the surface, since these influence the transfer of moisture, possibly resulting in bubbling of the floor coverings. It is a complicated subject, tied into osmotic action also, too long to discuss here.