Acclimating Lumber

Scott Seganti writes, “I ordered some lumber online for the first time and had a question about acclimation procedure. Bought some eight quarter Claro Walnut from Oregon where the average humidity is around 70%. The wood came in to this Arizona shop at 15-17% moisture content.” And by the way, this is not uncommon. We have not found a supplier yet that always ships wood that’s at eight percent. We’ve gotten some stuff from some of the best, most reputable dealers and it will arrive sometimes as high as 18%, so you can’t count on anybody supplying you wood that’s going to be ready to use. It’s up to you to acclimatize it, finish drying it, but Scott asks, “What do I do to acclimate this wood in a shop where this stuff is going to naturally equalize at five percent?”

We actually have a room that we use, we call it a drying room, it’s really a kiln where we finish drying wood that we purchase or finish drying wood that we’re drying from green, and in that room, the wood will get down to four percent. So, if we put wood in there that’s 17%, which is really pushing it, what I would do is sticker it. It gives about eight inches or so off the floor and put a, probably in the case of the walnut, you’d want to put a thin blanket over top to slow down airflow. What that’ll do is that will create a micro-environment inside that blanket.

So when you sticker it, sticker the top well too, so it holds the blanket off the top of the stack, so you’ve got air all the way around there in a really warm space. However you heat it, whether you’ve got a space heater, you’ve got a warm place in your shop, you want to create a micro solar kiln kind of situation, but you want the temperature to be pretty warm, 90, 100 degrees. Something like that, so that the idea is to move the moisture from the core to the surface at a similar rate that the moisture moves from the surface into the air. It’s that surface to air movement that creates a case hardening or cracking or stress, and as long as you can keep that moisture near the surface in the air, so that the wood as it dries off the surface, it’ll create a more damp environment under there than you’ll have outside of that blanketed environment. That will soften the blow from the environmental, the weather change.

Then eventually you can take that blanket off once it gets down around, I’d say, below 10% you can probably take the blanket off and then put a fan on it and finish drying it out. One of the things you’ll have to keep in mind, though, is that you’re going to get readings that are going to be, as your wood is drying and dropping in moisture content, the readings you’re going to get are going to be lower than the core reading. The core reading is going to be higher until it dries all the way out and then picks up moisture on the surface again and then you’ve got the opposite happening.

But just using your own judgment, when you think you’ve, I’m assuming you’ve got a moisture meter or you wouldn’t be giving me these numbers, when your wood gets down to around five percent, give it a few weeks after that before you start using it and hopefully there’s a place in there where you can make a cut or where, if you can cut where you would ordinarily have cut these pieces to make whatever you’re making out of it, meter that again right away and make sure that the moisture is uniform surface to core. That’s the biggest challenge in drying, particularly eight quarter pieces like that.

And walnut, all walnut, in particular this western Claro Walnut is, it has a tendency to hold pockets of water in places that you wouldn’t normally predict. So, you’ll want to check a lot of places on that and be very diligent about checking. And even after you think it’s completely dry and you start cutting your parts out, meter your parts all over the place because it’s surprising where you’ll find wet spots.

So, the main thing is just to really pay attention to it and I would monitor it every few days, just, not so much out of concern of the wood, but just to feed your learning curve and make notes. What was the temperature? What was the humidity in that area? If you can put a hygrometer inside the tent, the blanket, the tent, that will help tell you what the difference is between the environment the wood is in and the environment that you’re in. So all those little things. And it’s always an experiment. There’s not a uniform anything when it comes to drying wood, except in a controlled kiln environment. So, in a shop, there are always variables, so just keep paying attention and don’t come to any assumptions just, or conclusions, just because you’ve had some success. You want to keep gathering data and just keep learning because you’re never done. You’re always going to be in school until you quit paying attention.

So there’s a lot more about that. Our Bruce Hoadley talks about it in his book, Understanding Wood, and there are a number of places online that talk about drying. I think Virginia Tech is one of the places that has a good internet information on wood drying schedules. But it’s all a matter of moderating that humidity that’s directly around the wood and a simple blanket can do that. Thank you for the question Scott. Keep up the good work.

For those interested, check out what Scott’s doing over on his instgram page @segantiwoodworking

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