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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.

Kiln-dried lumber has the moisture baked out of it. It's not much different than the oven in your home. I can't tell you how long it would take in a kiln to get the moisture to zero percent. It doesn't matter because once you remove it from the kiln, the moisture content of the lumber will start to rise as it absorbs water from the air. It will stabilize to the humidity where the lumber is.

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.

Still Need Help? Type Your Keywords Here: (examples: drywall repair, pilot light goes out, poor lot drainage, crown molding guide, etc.) Your Facebook friends would love to know how this column helped you solve your problem. Type a quick comment of what you discovered here at AsktheBuilder.com. Thanks!

Comments: Welcome! I, Tim Carter, don't answer questions here. If you post a question here in the Comments Area, perhaps another visitor will help you. You need to go to the Ask Tim page if you want a question answered. Once there, look closely at how many weeks behind we are. Please be patient as you use this free service. If you have an emergency and need to talk to me, there is an option there for you. 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.      View all comments *Name: Email: Notify me about new comments on this page Hide my email *Text: Security Image: Security Image Text:   Remember, Tim Carter doesn't answer questions here in the comments. You need to go to the Ask Tim page.