Typical pinless moisture meter for testing moisture in a building. It is our mold inspectors meter being used by our client on his own wall.
Moisture Testing
Which is better during a mold inspection, moisture testing with a moisture meter, or moisture testing using water activity levels (aw).
Water activity level measurements are more accurate and are great for use in the food industry or in a laboratory.
However, moisture content readings with a moisture meter are much more practical during mold inspections in water damaged buildings.
What is Water Activity Level (aw)?
Water that is not chemically bound to a substance is called available water. Because it is not chemically bound, mold can have access to it. Thus, this water can support mold growth.
The term water activity level (aw) refers to the level of this unbound or available water.
Another way to look at it is the water activity (aw) of a substance is the ratio between the vapor pressure of the substance itself, and the vapor pressure of distilled water under identical conditions.
Typical pinless moisture meter for testing moisture in a building. It is being used by our mold inspector. Pinless moisture meters do not results in a dozen tiny pinholes in your walls.
Moisture Testing With A Moisture Meter
In the world of mold inspection and moisture testing inspectors do not typically use or even think about water activity levels. Such scientific measurements with such sophisticated methodologies are not needed. I have never seen a water activity testing instrument. Though it is a better measurement when you want to know if a substance contains enough water in the right molecular state to support mold growth, it is seldom used or widely known about in the mold and moisture testing industry.
The main advantage of testing moisture content with an old fashion moisture meter in a wet building is that a moisture meter can test many spots in real time during an inspection. Testing aw levels may involve chipping away at building materials and putting them in a chamber. Testing just a few areas for water activity is distracting. This will distract the inspector from doing more important investigations like looking for and smelling for mold and testing dozens of locations for moisture with a moisture meter. Most importantly, in a home or commercial building with wet building materials wet is wet. Because if you find moisture in a wet building material it is safe to assume that most of that moisture is available for microbial growth and not chemically bound.
Moisture meter showing high reading in a wet floor. If a meter indicates elevated water in a building during moisture testing then that water is available for mold to grow.
In Conclusion
It all boils down to this. It is true that water activity measurements measure the amount of water available for mold to grow. But in a home or commercial building with wet building materials, it does not matter. Because if you find moisture in a wet building material it is safe to assume that moisture is available for microbial growth. Thus, worrying about water activity levels and available moisture is pointless. If you find water in wet building materials then that water is available for mold growth. Just test it with a moisture meter. If moisture levels are high according to a moisture meter test then it is a problem. Moisture testing with a moisture meter is all you need. A moisture content of 16% is well-recognized as the limit for surface mold.
Sources:
http://www.masongrant.com/pdf_2008/Field_Moisture_Measurement.pdf
A Accredited Mold Inspection Service, Inc. Providing mold testing and moisture testing in south Florida since 2003.
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