I have a question. Has anyone out there had a problem with not stressing lumber after kiln drying, if it has been air dried first? The kiln operator says it only needs to be stressed (steamed) after the kiln drying if it hasn't been air dried to 10-12 percent first. A friend of mine says it should always be stressed. I haven't had a problem so far. All my oak is air dried at least 1 year. The lumber pictured is two-year air dried and down to 10 percent, then it goes in the kiln for a month and is taken down to 6 percent. I take it back to the shop and stack it inside. It usually sits there for a month or so before I start using it.
(Sawing and Drying Forum)
From contributor D:
I think someone has given you a lot of misinformation about drying lumber. I am guessing that you are talking about de-stressing, or conditioning, as it is commonly called. I believe most people will agree with me that you are going to extremes on the amount of time you are air drying. I would not let lumber air dry that long because of the risk of degrade, not to mention the fact I couldn't afford to keep that much inventory tied up. Oak can develop stress if allowed to air dry too fast in hot weather, but if it is kept in the shade and out of the wind, you should be okay. Also, the only way I could imagine taking a month to dry lumber from 10% to 6% in a kiln would be to leave the kiln shut off for at least 3 weeks.
In the past I have dried close to 100,000 bf of red oak 3-4000 bf per load in an Ebac dh kiln. I would air dry it to about 30% (1 1/2 to 2 1/2 months depending on the weather), then I would dry it in the kiln at a rate of about 1% per day. Drying this slow would not let any stress build up in the lumber. I never conditioned it and my customers said my lumber was the best they had ever used. I now have a Nyle and dry my oak at about 1 1/2% to 2% per day (still much slower than the big companies dry). At this rate of drying, I condition it for a few hours and have no problems.
I think if you look in the Knowledge Base here at WOODWEB, you will get a lot of useful information about drying your lumber. I think it would be advisable for your kiln operator to learn more about drying also.
I do agree with contributor D that such long drying time can result in excessive quality loss. On the other hand, long air drying for white oak will result in a vanilla aroma that the wood will have. Such wood is ideal for wine barrels, as the wine will pick up this flavor. But for all other uses, you are wasting time and perhaps losing quality.
I do agree with contributor D that your kiln drying time is too long. What is your average outside RH? If you can get the wood down to 12% MC, then it is 65% RH. Make sure that you start the kiln at a humidity no higher than 65% RH and preferably closer to 50% RH. Note that you cannot damage the wood at this point (except by over-drying).