Air Drying vs. Kiln Drying
Issue: Issue 1.05
Posted Date: 6/20/2000
From Wood Central
This wasn't a debate about the merits of both methods of drying wood so much as a rant about the practical application of air drying wood. The initial participant, a kiln owner, writes:
"I know that Krenov says air-dried lumber has a nicer feel under your handplane, etc. But in the last year, since I got my kiln, I have seen some horror story wood go through it that had been previously air-dried. It was moldy, checked, twisted, dirty, sunbaked crap that people deliver to have me make into flooring. None of it was actually dry enough to make into flooring, so it has to go in the kiln anyway. I'm sure that, had the lumber been correctly stickered, monitored in drying, and stored properly in a heated space, it would be fine. But that is really the exception. Most drying degrade happens soon after milling and is from too dry an atmosphere for the temperature. Most of the rest of the damage seems to be from leaking tarps rewetting lumber, direct sun, and grit splashed up by heavy rains."
Other participants agreed that, while air drying is preferable, it's rarely done correctly. One participant, a wood carver, advocates use of low temperature (below 180 degrees) kilns because the higher the temperature, the more brittle the wood becomes. This carver went on to say that low-temperature drying is often better than air drying and that getting the kiln to precisely 160 degrees "relaxes the wood and kills the critters."
The next woodworker commented on his solar kiln and how pleased he is by the wood that comes out of it. It does not, however, get hot enough to kill the critters, so he's going to add some supplemental heat to raise the temperature to 130 degrees (which he believes is the minimum for cooking the little creatures).
When possible and done correctly, the next participant commented, air-dried wood is nicer to work with and often has a better color. For more information on how wood reacts to air-drying and kiln-drying wood, check out Woodworker's Journal from February 2000 (page 21).