Our meter shows Doug Fir bottom plates at 25% MC. What does that mean? Let’s start with what it doesn’t mean. It’s not that the wood is 25% full and can only hold another 75%. The term is actually “moisture content by weight,” and it can be higher than 100%.
MC by weight is a comparison of the weight of the wood to the weight of the water in the wood, expressed as a percentage. Usually, a percentage compares part of something to all of something. With MC, we compare two different parts. Example: a piece of wood that weighs one pound (16 oz) and the water absorbed/adsorbed into the wood also weighs 16 oz, that would be 100% MC because they both weigh the same, or 100% of each other. If the water only weighed 8 ounces, the MC would be 50%. That’s how the MC can be more than 100%. The water can weigh more than the wood.
So, what is the meter telling us? Let’s say a piece of Doug Fir 2×4, about one foot long, weighs one pound (16 oz), and has a moisture content of 10%. The breakdown of the weight is:
Total Weight: 16 ounces
Moisture Content by Weight: 10% or 1.6 ounces of water
Weight of Wood: 16 ounces total – 1.6 ounces of water = 14.4 Ounces of wood
So, that piece of wood with a 10% moisture content weighs 14.4 ounces, and the water in the wood weighs 1.6 ounces. When determining moisture content, it’s important to understand what we’re measuring!
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