A lot of contractors have to deal with concrete moisture content for one reason or another. Some are checking to make sure that freshly-installed concrete is dry enough to install other flooring systems over it, others may need to make sure that the concrete hasn’t absorbed too much water from a flood as part of a water damage remediation/restoration job. Regardless of the reasons, professionals need a reliable and accurate means of testing concrete moisture.
Many contractors ask if there are concrete moisture meters available that can accurately read the moisture content of concrete. In fact, some manufacturers offer “concrete moisture meters” that they claim are optimized for testing concrete moisture. However, to accurately measure moisture in a material, there needs to exist a reliable and proven moisture reading scale for that material.
With that in mind, is there such a thing as a concrete reading scale for moisture meters?
The Short Answer
No. There is no such thing as a universally-applicable concrete moisture reading scale for moisture meters.
Why Isn’t There a Concrete Moisture Reading Scale?
Why isn’t there a consistent moisture testing scale for concrete when reading scales exist for materials like wood, drywall, paper, hay, or grain?
Well, the reason is that these other materials tend to have consistent physical characteristics from one sample to the next (at least, within the same species for wood, grain, or hay) that can be used as a “baseline” to test against for moisture content. Concrete, on the other hand, does not.
There are too many variables between different mixtures of concrete to establish a consistent standard to use for a concrete reading scale. Even two bags of concrete made by the same manufacturer might have a major difference in the size of the rock, sand or gravel pieces used as an aggregate material.
For pin-type moisture meters that use electrical resistance to measure moisture, this would mean that two batches of concrete that are equally dry might have a different amount of electrical resistance—resulting in disparate moisture content (%MC) measurements despite actually being at the same %MC.
For pinless moisture meters, the size of the rock, sand, or gravel chunks in the concrete can affect its specific gravity. This distorts the radio frequency used to scan the material in different ways, throwing off the meter’s accuracy. Even the distribution of aggregate materials in concrete could lead to changes in the moisture measurement of the concrete in such cases.
So, How Can You Accurately Check Concrete Moisture?
If moisture meters don’t have a proper reading scale for concrete, then how can you accurately measure moisture in concrete? The best method is to use the ASTM F-2170 concrete moisture testing standard.
Here, instead of trying to use a moisture meter to directly test the amount of moisture in concrete, you would use a thermo-hygrometer (a.k.a. an RH meter) with an in-situ probe to test the relative humidity (RH) conditions deep in the concrete.
This is a more reliable and accurate measure of the moisture in concrete because it gives you a measurement of how much moisture the concrete slab is releasing into the air—which lets you know whether enough moisture is being released to pose a threat to other building materials above the concrete, or if the concrete is at risk of developing other problems.
Need the right tools for testing concrete moisture? Contact the experts at Delmhorst Instrument Co. today.