Over-dried lumber
November 1, 2013 | 7:00 pm CDT

Q: We bought some green lumber and had it kiln dried here. This lumber seems in some pieces to have a lot of cup, end splits and side bend. Is this a drying problem?

A: There are many causes for the defects that you mention. Side bend is often a result of poor sawing practices; end splits are a result of not using an end coating on the logs and lumber; and cup is a natural event for flat sawn lumber from small logs. However, all three defects are accentuated by over-drying. (Poor gluing and poor machining also result when wood is over-dried.) Over-dried lumber that is brought back up to the correct MC will still behave poorly.

When we discussed this problem further via e-mail, you mentioned that you have recently instituted a new program directed at avoiding wet lumber after drying and in storage. I will take a guess that your kiln operator is so concerned about avoiding wet lumber with your new "No Wet Lumber" program, that he over-dried a small portion of the load. He needs to make sure that he gets both dry and wet samples when running the kiln. He needs to use an equalizing step in the schedule. In essence, your moisture program needs to be renamed the "100% Correct Moisture Content" program, as you need to avoid both overly wet and overly dry lumber.

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About the author
Gene Wengert

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 45 years. He is extension specialist emeritus at the University of Wisconsin-Madison.