Working with lumber

I am buying some kiln dried lumber for a project and could use some guidance. I've always been a little confused on the MC of wood. I know kiln drying gets moisture much lower than air drying, but if you leave the wood for a year after kiln drying it, does the MC return to where air dried lumber would also be?..and if so, is the only benefit at that point that any bugs in the wood should be killed off?

I had planned to acclimate the boards to the environment they'll reside in when the project is finished (basement)...but if the completion could take weeks or a month -- what are best practices for keeping the boards acclimated or is it not such a big deal? I'll be working in my garage, so should I re-acclimate after jointing, planing and length is cut and before assembly?

While people disagree on the relative benefits of air vs kiln drying, kiln dried wood will definitely change in EMC to that of the environment. For example, KD to 9% will gladly return to 15% or so if stored in an unconditioned space, depending on the location, local environment, wood type and thickness, and time. And even in one location the EMC can change from month to month.

I rarely build furniture but from my reading, the change you mention can happen from shop to house and from house to different house if the furniture is moved at some time in the future, the reason certain joint practices exist. I suspect some with good experience will chime in with their methods of work.

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Originally Posted by john schnyderite

I am buying some kiln dried lumber for a project and could use some guidance. I've always been a little confused on the MC of wood. I know kiln drying gets moisture much lower than air drying, but if you leave the wood for a year after kiln drying it, does the MC return to where air dried lumber would also be?..and if so, is the only benefit at that point that any bugs in the wood should be killed off?

I had planned to acclimate the boards to the environment they'll reside in when the project is finished (basement)...but if the completion could take weeks or a month -- what are best practices for keeping the boards acclimated or is it not such a big deal? I'll be working in my garage, so should I re-acclimate after jointing, planing and length is cut and before assembly?

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You should state where in the world you live. Local humidity can vary a a lot during seasonal changes. Is your house or shop heated in winter?
Bill D.

Also unless you live in a climate controlled house the MC will change with the RH in much of the country. I live in northern NY and during the heating season wood dries out, and during the summer when the humidity is high the wood takes on moisture. This does limit what can be done with wood, to some extent, but there are ways to do whatever you're doing that will minimize the potential for problems.
Zach
EDIT: Sorry, simultaneous typing....

I live in New Jersey. My garage/shop is not heated.

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Originally Posted by Bill Dufour

You should state where in the world you live. Local humidity can vary a a lot during seasonal changes. Is your house or shop heated in winter?
Bill D.

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Aside from certain heat processed products that change chemically so they no longer tend to absorb moisture, both KD and air-dried lumber will acclimate to local humidity conditions seasonally. Designing/building with wood movement in mind will account for that. Milling evenly from both sides of the material will help, too.

Timber does move over time and with the seasons. That is why there are widely accepted principles used for working with timber.

In your situation, assuming that the kiln drying was done correctly, get the machining and assembly done without delay. This is how it has always been done in commercial workshops - dry timber and get on with the job. Leaving timber lying around is inviting it to turn into boomerangs. Cheers

The only thing I'd like to add to what others have said is that you should let wood acclimate to your shop before using it, even if the RH changes as it is acclimating which it likely will in an unconditioned shop like yours - and many others. The worst thing to do is to bring wood into your shop at saw 14% RH and start using it if the EMC in your shop is 6% at the time. Yes, it can be done, but the odds of cupping, bowing, etc. are much greater than if you let it acclimate for at least a couple of weeks before using it. But don't guess. Get a moisture meter and use it. The best way to know what the EMC of your shop is is to measure the MC of wood that's been in your shop for many months. And hang a RH meter on the wall along with a RH vs. EMC chart. That will tell you where your wood is headed.

John

I am penalizing this thread 10 yards for overuse of undefined acronyms. :-)

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Originally Posted by Ken Kortge

I am penalizing this thread 10 yards for overuse of undefined acronyms. :-)

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Good call. While acceptable in the football world such sloppy writing is unacceptable in a respectable technical document such as this.

MC - moisture content
EMC - equilibrium moisture content
RH - relative humidity
KD - kiln dry or kiln dried

And going for the TD,
NY - New York
:D

They ain't acronyms unless they can be pronounced as a word. They are mere abreviations. And promotion is unlikely.

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Originally Posted by Mel Fulks

They ain't acronyms unless they can be pronounced as a word. They are mere abreviations. And promotion is unlikely.

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Ha, you're absolutely right! Just EMC perhaps, but that would be more likely used at a disco.

JKJ

Know your MC of the wood you are using, know the expected EMC of the location where it will be located... Check on how much the wood will expand/contract under those conditions and build the project allowing for that amount of wood movement.. There are programs on the net to calculate this..

I use both air-dried and kiln-dried in projects but measure MC before/during construction to allow for expected movement and have not had any major problems yet.. (though I will now probably since saying that !! )

One advantage of properly kiln dried lumber is that there will be fewer defects show up, such as cupping, warping, etc.... THIS IS MY EXPERIENCE AND OPINION ONLY.. i am sure others will disagree on this !!

John
My shop, and all of the wood I have, is in an unheated, non climate controlled, garage shop in CT. If I am building something for inside the house, I bring the roughly sized materials into the house and let them reach them equilibrium. It's a pain in the butt to walk back and forth to the garage shop from the house with the material, but it has to be done. So far it's worked for me.
I can, and have stored, larger quantities in the basement. There is a dehumidifier down there and we run a wood stove through the winter.

I have 600-700 bd/ft of walnut in slabs that has been air drying for about three years now and can't decide whether it should be kiln dried, or not. I go back and forth on the issue.
Some has to be steam bent which is why I bought it the way it is, but not all of it.

I heat my shop, not as warm as the house, but allow no freezing, and warm it up about every day, so it is nearly as dry as the house. Also store lumber in the shop, and bring in lumber so it will be acclimated when used. Really works well for me.