Kiln Lumber Drying
DEAR TIM: You mentioned moisture content in new construction can continue to dry and cause cracks in walls. Can you elaborate on moisture content? If kiln dried, is moisture reduced to 10%, etc? How long for moisture to get to 0%? Dave G, Red Bluff, CA
DEAR DAVE: Lumber is a hygroscopic material. This means it can absorb moisture in both liquid and gas form through its very open cellular structure. Think of a tree when it's standing up as a massive bundle of very tiny straws packed next to one another like the straws jammed into a canister at an old-time soda shop. Cut off the end of a piece of lumber exposing a fresh edge and then paint the end with some water. You'll see the water disappear into the wood as if there was a vacuum attached to the other end of the piece of lumber.
It's impossible to air dry lumber and get it to zero percent moisture content. There are very few, if any, places on Earth where the relative humidity is always zero. You may get it close if you set a piece outside to dry in the Atacama Desert.
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robert mcwatty 14 Oct 2010, 10:39
My house was constructed in 1958. My termite inspector has told me that
the mositure content of the wood under my ground level floors is 26%. I
have outside vents and a fan that comes on when the moisture increases. I
did not feel that seasoned southern pine lumber used in house construction
after that many years could pick up air moisture to that high a level. I
live in S. C.
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