Moisture Content Percentage Explained
Experts explain why wood moisture content can be higher than 100 percent. February 15, 2009
Question
In on of the new Woodshop News magazines, there is an article on wood warping. It states,"when a board is cut from a log prior to a trip through a kiln or a period standing in a stack to air-dry, it is saturated with moisture. It can have a moisture content of 100 percent. That is to say that there is as much weight of water in the board as there is weight of dry wood tissue." Is this correct, or is it just in some species? It just doesn't seem right to me.
Forum Responses
(Sawing and Drying Forum)
From contributor D:
From Gene Wengert, forum technical advisor:
Many people think that's impossible, they are thinking volume. Weight measurement makes sense, if you think about it.
From Gene Wengert, forum technical advisor:
Indeed, it is correct. Lumber MC is measured as the weight of water compared to the weight of dry woody material. The MC of particles, fuel, pulp and a few other items are measured as a % of the total weight that is water. The lumber MC is called the oven-dry basis, while the other method is the wet-weight basis. The wet-weight basis makes more sense to engineers. Note that both systems are based on weight.
Example: green weight is 3 pounds and the oven-dry weight is 2 pounds. For lumber the one pound of water is 50% of the weight of dry wood, so the MC is 50% MC. For fuel, the weight of water is 33% of the total weight, so the wood is 33% MC. In other words, 50% = 33%.
From contributor J:
Saw some bacterially infected red oak and you will see how MC can be over 100% of the dry weight. It smells bad too.
From Gene Wengert, forum technical advisor:
Cottonwood, sinker hemlock, and eastern red cedar are often over 100% MC (or 50% MC).
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