I recently picked up a couple hundred board feet of red oak (freshly sawed). I have managed to locate a source to kiln dry the wood, however I am concerned about the process he uses. He has explained that he does not use a conditioning cycle to add moisture at the end of the drying process (because he runs the kiln at a lower temperature). I am far from an expert on drying wood but most everything I have read leads me to believe that the wood will be unstable without conditioning at the end. Should I be concerned or am I all set?
Thanks!
Replies
It really depends!
I've used methods that condition the wood and some that don't If the outside air temp is high and the humidity level is low just about any method works fine.. If the humidity is very high and the kiln very dry you may have a problem..
You can condition the wood yourelf you know, not hard or complex...
I'm a fan of air-dried lumber. If you think of it, kilns were designed and built for speed and production, not quality of lumber. You'll get better quality lumber with better machinability if you air dry it properly. Besides, it's free!
Gene Wengert, professor emeritus from UW-Madison has written several extension newsletters on air drying lumber. Do a Google search for plenty of resources.
Here's the basics: Find a place outside with a good breeze. Start with 5-6 rows of concrete blocks 4' long parallel to each other for 8' boards. Use 3/4 x 1" stickers (I use 1/2 x 1 stakes bought in a bundle at Lowes). Lay down 1 row of stickers on the concrete blocks, followed by 1 layer of wood, stacked edge to edge. Follow with another layer of stickers, then lumber. Keep going until you're done, then top with another layer of stickers, a sheet of plywood for cover, and as many old concrete blocks, rocks, or scrap steel you have around for weight. Give it 6-8 months of patience (for 1" lumber) and your lumber will be dry.
The only trick with air-dried lumber is that you need to bring it into your shop environment 2 weeks before you machine it. It will acclimate to the temperature and humidity and work just fine. I've had really good luck.
I think your kiln-dryer is right. Because he's drying wood at a lower temperature, the wood retains moisture longer than drying it faster at a higher temperature,(for the sake of argument humidity/temp are the same for both equations).
Drying it this way is also closer to air-drying, a time-proven technique. Just to be sure, take a sample of oak and rip it to check for case-hardening, a condition which can sometimes arise if steam is not injected into the kiln.But as long as he carefully monitors the process, it should be okay.
Thanks for the suggestions guys!
I did not think I would be able to achieve the 6-8% moisture content that I would need by air drying. I have only used air dried lumber on a few occasions, typically I saw 10-14% moisture content (dried for 3+ years). I am certainly not opposed to air drying if it will yield the quality and moisture content I am looking for. What moisture levels have you guys been able to achieve through air drying?
Back to the kiln drying conditioning cycle....let's just say, worst case, I get the wood dried to 6-8% and it is case hardened. It makes sense to me that I could let the wood sit in my basement shop for a year and it would reach a "moisture content equilibrium", essentially getting rid of any case hardening. Am I correct in my thinking?
I'm concerned with your thought process. If wood sits around at 10 to 14% moisture after three years why would you ever believe that you need to dry it to 7%?
Take a meter and measure the wood in your house.. if it's 7% then you can air dry it to 7% if it's higher then that's all you can dry it to.. If it's kiln dried to 7% it quickly returns to 10 to 14% why bring it down to 7%? Is there something magic about that number?
"If wood sits around at 10 to 14% moisture after three years why would you ever believe that you need to dry it to 7%?"
My thoughts exactly. There is nothing special about 7%. Wood is a big sponge and is going to try to reach equilibrium with the moisture in the immediate environment. That 7% wood isn't going to stay at 7%. The minute it comes out of the kiln, it is going to start gaining or loosing mosture depending on the RH.
To the original poster: Unless you are in a big hurry, or drying one of a handful of "trouble maker woods" like beech, why not air dry?
What ever route you take, bring it in your shop for at least a couple of weeks, rough it slightly over size and then let it sit for at least a couple of more days befor milling it to size and doing joinery.
Busto
Some people read something and it's bible to them.. It reminds me of the old saw, a little bit of knowledge is a terrible thing..
Fdampier- I think you have jumped the gun a bit here in concluding that whatever I read I think is "bible". Nothing could be further from the truth, in fact, that is why I am here asking questions in the first place. I had already checked the MC of many items in the house at various times of the year and found that 6-8% was roughly average. Also, as you say "a little bit of knowledge is a terrible thing", but doesn't everyone (including you) have little knowledge at one point? In any case, thanks for the suggestions.
Thanks for all other suggestions. I am still open to air drying if I can achieve what I am looking for.
What I do to ensure that the wood I'm working with is dried to the level it needs to be is store it where it's going to be used.. I'm certain that you have a corner of the house where you can stash the required number of boards for a while. I've used under the bed and in a closet and in the rafters of the basement.. Here during the summer wood tends to swell with the moisture in the air so if it's brought into the airconditioned house it quickly drops to lower numbers, 12% turns to 7 percent in less than a month and sometimes a week or two..
Same with the heating season. I can bring wood at 25% moisture into the house and three months later measure it at 8%.
What you really want to do is not achieve any magic number but remove thebond water, that is water that is part of the makeup of the cells in the wood.. once it is free, it really only matters a little bit what the moisture content is.. Take a stick that is dried to 7% and put it in a humid location and it will quickly swell with water.. That means it will measure 10% 12% or even more. who cares? If you work on wood it will quickly return to the moisture level present in the atmosphere. Seal it with a varnish./paint tec. and it will take a bit longer but will eventually return to those levels..
>> What moisture levels have you guys been able to achieve through air drying?
Depends on exactly how you define air drying. If I bring wood that has been air dried to 12% into the house or other similarly heated space in the winter in Boulder, getting it down to 6 - 8% would be like falling off a log. <yuk yuk yuk> I wouldn't call that kiln drying, but you might not think of it as air drying, either.
My experience is that once oak is case hardened, it remains that way.
Edited 6/3/2004 3:05 pm ET by JACKPLANE
Entropy, unless the kiln operator you have talked to is bringing the wood up to temperatures that will liquify the fatty acids in the lignin (at least in the 170 to 190F range) he wouldn't need to relax the wood with a late schedule steaming...Of course, he really isn't "Kiln Drying" the wood in the conventional sense either...meaning, his process really isn't reestablishing the wood's stress base point relative to humidity.
Basically, all he is doing is speeding up the air drying process with a little mild heat. In reality, what you will have is essentially air dried wood, only you'll have it a few months earlier than if you air dried it in the conventional way at ambient temperatures.
I guess it's your choice. Are you in a big hurry? Red oak is not a particularly difficult wood to air dry. Unlike white oak, it lacks tyloses in the cell cavities and gives up moisture relatively quickly.
(we just covered this topic in detail on a recent thread here at Knots. You might want to check the archieves.)
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