Vacuum-Dried Wood

[Irvin Cooper]

Good afternoon all.

I am on the cusp of purchasing some walnut to build a bed. When speaking to the owner over the phone about wood they have in stock, they replied that they would "put it in the kiln tonight" and I "could pick it up later this week".

I asked how that was possible, since all of the drying kilns I was aware of took weeks/months to dry, not just a matter of a couple of days.

This outfit uses what is called a vacuum kiln, where they have some sort of metal pan of water in the bottom of the kiln, then load the kiln up and dry it under vacuum pressure.

Has anyone ever bought lumber which was processed in this way, and how did it hold up? I am hesitant to drive all the way up there and purchase lumber that could become 90% waste wood because it wasnt dried properly.

It could be that all lumber is dried this way and I am just not very well informed.... I thought it was all dried by long-term exposure to moderately dry heat.

Thanks.

Irv

[Lee Schierer]

Under a deep enough vacuum water will boil at room temperature. I don't know if the water contained in the cells of wood would boil off if pulled in a vacuum. Generating a vacuum on a large cjhamber would get rather pricey depending on how low they need to go to "dry the wood".

[Darren Duchi]

In fact it is supposed to be very mild on the cells of the wood. One thing that i can attest to was very little downfall in the lumber that we were having dried (Oak). One thing that was definately different was color in the sample that we had vacuum dried. Hope this helps

[Irvin Cooper]

Darren,

Can you expand on that a little? Have you used vacuum-dried lumber? Was the color better or worse?

Thanks.

Irv

[Darren Duchi]

Hello Irvin; Yes my company has done some research on using vacuum dried products. The species that we have experience with is Tan Oak. Which is more of a weed in Northern California. It is a rustic product that is very hard to dry and process. The differences that i have seen are that the tan oak when dried conventionally has a tan/brown color more closely compared to white oak. When dried in the Vacuum kiln the color was very pale white and was not desirable in that instance. We noticed that there was very little downfall in the way of check/warp/twist/ in the vacuum kiln process as opposed to the large kiln conventional methods. I have since given the lumber away to a friend to make bunkbeds for his grandkids. Vacuum Kiln Drying has been around a long time but only works on small volume type situations. Combining lower temperatures with controlled extraction of water from the cells of the lumber make this viable to create good products. Many industries use this technology. Baseball bats, and many other billet style drying situations create less fall down therefore are a winner in those situations.