Q: I would like to see if I could get some literature on the most critical time when kiln drying lumber. My boss seems to think it's at fiber saturation point,30 percent MC. I would like more information.

A: The most critical time for drying lumber (to control checks, cracks, honeycomb, warp and stain) is above 45 percent MC. This high MC is when all the defects are formed. By the time you get to 30 percent MC or lower, the quality is pretty much already determined. Being very specific, for air-dried lumber, any drying quality loss is determined by what happened in air drying and not what happened in the kiln unless the lumber regained moisture when it went into the kiln. There are three "defects" that occur at low MCs: incorrect MC, casehardening stresses, and some cupping.

This topic is discussed in Drying Hardwood Lumber . Do you have a copy? Free copies are available from U.S. Forest Service, Wood Education & Resource Center, 301 Hardwood Lane, Princeton, WV 24740. Phone: 304/487-1510. Fax: 304/487-6661. E-mail: education@werc-hdw.com .

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