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AndrewPritchard

Pros and cons of air dried vs kiln dried

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I have the opportunity to buy some pretty cheap wood - oak, maple etc. from a backyard sawyer. He air dries some of his lumber and kiln (I'm guessing solar kiln) dries the rest. The air dried is considerably cheaper ($1.25 CAD bft) than the kiln dried ($2 CAD bft).

All things being equal (ie they are both below 10% moisture): which is better?

I had heard that air dried is better because the drying process puts less stress on the internal structures of the wood and so is more stable, but obviously commercial organisations don't want to wait that long to be able to sell their product so they kiln dry instead.

Is this true?

Should I just stump up the cash and buy the kiln dried, or is the air dried actually preferable? 

 

I've only ever bought from larger commercial organisations, where I've known more what I'm getting. I've seen some red oak that a friend of mine bought and it looks ok, although he did comment that it wasn't quite dried so it had moved on him during the construction of his project. (His piece is coming out beautifully). But that movement could have happened regardless of how dry it was - right?

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A topic I've thought about and read about a lot. I mainly use air dried, but there are some things that I do to prevent problems. 

First, one misunderstood principle is that wood will acclimate to the environment it is stored in. Meaning, if you store air dried and kiln dried in your shop, they will eventually be the same moisture content. That can occur either through air dried drying more, kiln dried picking up moisture, or a little of both. So if you have a climate controlled space to store lumber, or better yet, your shop is climate controlled, than in the end moisture content of your lumber will not be based on the method used to dry it, but rather based on where you store it. 

I use air dried because I mill it and don't have a kiln. I can get my wood down to 10-12% outside, then I bring it into my shop and can get it down to the 8-9% range. Not quite as low as you'll get when you put your finished piece in a climate controlled home, so I plan on some movement. But we all need to plan on some movement because even in a home the moisture content will change with the seasons. Where I live in the mid-Atlantic region the swings in humidity are pretty dramatic. 

From my experience in working with air dried, the slow process of drying results in very little built in stresses. I think the colors are more vibrant in the air dried and I sense that air dried is a little easier to work with hand tools. Also, I really like having access to wood with different moisture content. If I'm doing bent lamination I like to use the "wetter" wood, just seems more forgiving. There are also other procedures, especially in chairmaking, where if you use wood of different moisture contents than you can achieve a tighter joint.

The big issues with air dried are bugs and pitch setting. Kiln drying will kill a bugs and bug larvae. But kiln dried wood can still become infected if store with infested lumber. I spray my lumber with a borate containing spray that helps prevent bug issues. I also like to get the bark off of my boards. But I am still very vigilant about the possibility. In pine you need to raise the temp high enough that the pitch "sets" in the wood. These, in my opinion, are the two main advantages in buying kiln dried lumber. 

But, with that said, I'm not sure you can get the high enough predictable temps for a long enough time in a solar kiln to kill bugs. Perhaps someone with a solar kiln can help with this info. If you can't predictably kill bugs in a solar kiln, than in reality, with what I said above, you may as well just buy the air dried. Just check the lumber carefully for any bug issues before buying.

 

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You can bend kiln dried but it's not easy.  Air dried is more suitable to bending if you have those type of projects.

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Nut, you very well may be right that it's the steaming that diminishes color, interested in hearing other thoughts. I've always attributed the vibrant coloring I see in air dried walnut as a result of it being air dried. Then I learned from Spanky it might be from cow pee. Never heard that before but I do get most of my lumber from hedgerows that grew along cow pastures.

I will say I've always been biased in this debate because of processing my own wood and air drying it. Have worked with kiln dried, but not to the extent that I have with air dried.

In reading Krenov, he often talked of his dislike of kiln dried wood and the way it worked with hand tools, always found that interesting. I haven't worked kiln dried with handtools enough to know. 

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I don't know man i say that because I've bought some really nice and colorful KD stock and I've also bought some junk.... I know there is a ton of variation in cherry and walnut tree to tree but it makes you wonder.

25 minutes ago, Bmac said:

n reading Krenov, he often talked of his dislike of kiln dried wood and the way it worked with hand tools, always found that interesting. I haven't worked kiln dried with handtools enough to know.  

Could also be experience. I think automatic transmissions are the devil and should burn in .... but that doesn't make manual transmissions better or autmoatics worse. That being said if someone like Krenov has that strong of an opinion i'm inclined to believe him. The only time Air dried gave me issues is with a hand plan on curly wood.

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I don't have a bending project planned, but I might consider one in the future. I did one recently and I think it came out well :D

Has anyone found thicker air dried to be more problematic. This guy is selling 10/4 and 4/4 (not sure why 10/4 - but that's his specs), and I'm just a bit concerned that the centre of the 10/4 isn't going to be dry enough to turn into 2"x2" table legs (for example). To set my mind at ease, should I buy the kiln dried 10/4 and the rest of it air dried?

I realise some wood just moves, and there's nothing you can do about that. It's the nature of the material. I'm just trying to improve my chances given the rather substantial price difference.

 

I have access to a heated workshop, so I'll probably buy the wood and leave it there for a couple of weeks. It's a community shop so I'm going to have to mark it up as belonging to me so no one else uses it "by mistake". The place I'm considering leaving it is right by one of the air filters which are left on 24/7 and I can arrange it so there's a constant air flow over the boards. I'd sticker it so the stickers run along the length of the boards so the air can flow all the way down. I'm sure that would help with the acclimation process, but can you foresee any other problems with doing that?

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The thicker air dried will dry, just takes some time. Oak is notorious for drying very slowly when cut thick like 10/4. I would ask the guy how long the stuff has dried. Drying the thick stuff is even difficult with a kiln, so there is no guarantee the kiln stuff will be completely dry. I've cut into thicker boards, I mill up a lot at 9/4, and even though the outside is reading 8/9%, I've gotten higher moisture readings (12-14%) inside the boards. When that happens I cut my pieces to rough size or resaw to rough size and let them sit in the shop stickered for a month or two, that takes care of it. 

Another thing to consider, how is this guy storing his kiln dried stuff? If it's sitting outside or in an unheated uncontrolled space, in awhile the moisture content between the air dried and kiln dried will be the same.

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Since thicker boards take longer to dry, if these aren't already dry enough expect the possibility of some checking on the ends as the ends will dry at a different rate from the rest of the lumber.  Consider sealing the ends with latex paint or some of the other products made for that purpose.

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On 3/31/2019 at 9:16 AM, Byrdie said:

You can bend kiln dried but it's not easy.  Air dried is more suitable to bending if you have those type of projects.

I had limited success after soaking kiln dried lumber for 24 hours in water, prior to steam it.  I could not find air dried walnut in my area.

martin

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