Preventing Drying Damage to Oak

Advice on controlling the drying conditions for Oak. December 6, 2009

Question
Does anyone have trouble with degrade on oak when drying with a dehumidifier kiln? I air dry first but I seem to have better results from green. It's that last drying from 16%-10% that seems to create problems. Has anyone tried adding water in the kiln at the end of drying to get good results?

Forum Responses
From Professor Gene Wengert, forum technical advisor:
Except for cup, all other degrade is the result of improper drying at much higher MCs... above 45% MC for oak. Because the wood is so strong at 16% MC, it is virtually impossible to initiate new checking or honeycomb degrade. Further, staining is also a high MC event. Because air drying is uncontrolled (drying rates can be too fast or too slow, and rewetting can occur from rain), air drying can cause a lot of degrade. That is why shed drying is often preferred for oak.

Adding water to partially dried lumber can create a tremendous amount of interior checking as well as some surface stain.

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From the original questioner:
I have just loaded the kiln with oak at 20%, air dried boards, initial kiln temp of 38 degrees c, but wet bulb of 29 degrees. I am worried that I cannot control humidity for a safe drying rate. Any suggestions?

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From contributor T:
As Dr. Wengert said, I also tell people that once the wood is below 25% MC, you generally cannot do any drying damage. If anything, I would raise the temperatures up some if possible, to speed the drying. Oak and other species that require more controlled drying are best put into a kiln green, where you have the ability to control the conditions.