Tools of the Trade: Moisture Meters
A moisture meter is a simple, easy-to-use tool for evaluating moisture and mold problems
Moisture meters help you figure out whether your building materials are too wet. They typically use electrical conductivity between a couple of metal pins to assess moisture content; the more moisture in the material, the greater the electrical conductivity. The moisture content is measured as a percentage of total weight.
The meter pictured at right (www.delmhorst.com) can be used on a variety of building materials — wood, gypsum board, and concrete. For wood, the green light goes on if the moisture content of the wood is below about 15% or so; the yellow light signifies between 15% and 20%; and the red light comes on above about 20%.
Wood that has content above 15% inside a home suggests a moisture problem. Marginal decay occurs in wood starting about 20%. Wood reaches fiber saturation somewhere between 25% and 30%, also about the range where wood really starts to rot.(For more information on types of moisture meters and how they work, read “Electric Moisture Meters for Wood”).
Moisture meters can come in very handy
Builders can use moisture meters to know when to close in framed walls, lay hardwood floors, or install sheet good flooring over concrete. Building scientists can use them to track and identify moisture problems or investigate hidden mold behind closed walls.
The picture at right is a good example: What does a moisture content reading of 17.3% in the bottom of this crawl-space stud tell us? Using this equilibrium moisture content (EMC) calculator, it tells us that the stud's moisture content is higher than it should be in this relatively dry crawl space.
The wood is getting wet somehow, but how?
Stay tuned; next week I'll reveal the answer. In the meantime, use the comment box below to guess — the first correct answer get's an official GreenBuildingAdvisor carpenter's pencil (actually, it's a Fine Homebuilding carpenter's pencil — we don't have any GreenBuildingAdvisor pencils yet).
- Peter Yost
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