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Kiln-dried vs air-dried maple?

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Kiln-dried vs air-dried maple?

Postby Dave Locher » Thu Oct 15, 2015 5:00 pm

I am shopping for maple for my 2nd build. I'm doing my shopping online, unfortunately. I am seeing "kiln dried" and "air dried for (x) years" for sale from different sources. Most then say moisture content is in the 6-10% range, depending on the vendor.
Does it make any difference? Is there an advantage to either method of drying wood?
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Re: Kiln-dried vs air-dried maple?

Postby David King » Thu Oct 15, 2015 7:40 pm

I think depends on what you are building and what sort of kiln drying process was used. Violin makers tend to be fussy about using air dried only. For electric solid bodies kiln dried ought to be just fine. That said a kiln can ruin any piece of wood if the correct schedule isn't followed. Some woods are a lot fussier than others. Some maples cut in the growing season almost have to be kiln dried to get the sap out before the wood gets bacteria stains.
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Re: Kiln-dried vs air-dried maple?

Postby Barry Black » Thu Oct 15, 2015 8:58 pm

If air dried is available I would go for it. When I retired from building furniture for a living I ended up with quite a bit of wood which had been stickered on my racks for up to 18 years. Since then I have used it in projects along with freshly purchased kiln dried and have noticed a huge difference mainly in it's stability.
I have also heard that there are sometimes nasty chemicals used in the kiln drying process which is why it is not recommended to use kiln dried oak chips to flavour home made wine :)
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Re: Kiln-dried vs air-dried maple?

Postby Dave Locher » Thu Oct 15, 2015 10:45 pm

So air dried is possibly better and more stable? That is great to know. Thank you!
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Re: Kiln-dried vs air-dried maple?

Postby Larry Davis » Fri Oct 16, 2015 8:33 am

David King wrote:Some maples cut in the growing season almost have to be kiln dried to get the sap out before the wood gets bacteria stains.


(sigh) Bacteria can give you anthrax and pneumonia , but does not stain wood.
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Re: Kiln-dried vs air-dried maple?

Postby Barry Daniels » Fri Oct 16, 2015 10:52 am

That would be fungi that stains wood.
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Re: Kiln-dried vs air-dried maple?

Postby David King » Fri Oct 16, 2015 12:01 pm

Apologies to all, mushrooms it is.
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Re: Kiln-dried vs air-dried maple?

Postby Alan Carruth » Fri Oct 16, 2015 1:59 pm

Improper kiln drying can certainly ruin good wood, but so can improper air drying. I've seen plenty of examples of both.

It's possible to dry wood down to the 6%-10% range by either method. What counts is what's done with it afterward. It always amuses me to see a stack of 2 x 4s out in the rain with a sign that says: "Kiln dried". Wherever it is, it's going to assume the equilibrium moisture content that goes with the local relative humidity, and do it fairly quickly.

Stability is probably more a function of the age of the wood than how it was dried in the first place. All freshly cut wood has some built-in stress, and that tends to work itself out over time. In the process the wood will move some, and, of course, if you cut a piece of wood that has such stress in it, it will move too. For example, trees tend to put on new wood in tension relative to the wood underneath. If you take a quartered plank and cut a slice off the 'bark' side, it will tend to curve away from the board at either end. This can also make it difficult to cross cut a quartered board in from the bark side, as the tension causes the cut to close in on the saw. Wood that has been cut for some time is less likely to do this, all else equal.

Another thing that contributes to stability in older wood is hemicellulose degradation. Hemicellulose is a sort of 'filler' in the lignin 'glue' that holds the cellulose structure of the wood together. Hemicellulose is also the part of the wood that absorbs moisture from the air. Over time it breaks down, and the wood has less ability to absorb moisture, so it becomes more stable.

Stress reduction and hemicellulose degradation are probably most of the difference between 'dry' and 'seasoned' wood. Since both tend to proceed faster if there are swings in humidity and temperature the old practice of storing wood in a drafty shed out of the rain and snow makes a lot of sense.
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Re: Kiln-dried vs air-dried maple?

Postby Dave Locher » Fri Oct 16, 2015 3:00 pm

Thank you, Alan. That is exactly the information I needed to know to make a better-informed purchase.
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