moisture equilibrium question

[Jeff Cord]

I have recently purchased a bunch of doug-fir to build a workbench and am waiting for it to dry.
According to the current FWW based on the current temp (70 degrees in my garage) and the relative-humidity (30%) I should expect the wood to reach equilibrium at at 6.2%.
Is this true?
In the past 2 weeks the driest of the wood has fallen from about 14% down to 12% (some of the wood was over 20%).
At this rate it will take weeks to fall to 6.2%.
I realize this is for a workbench but want to do things the right way so I am really curious if I should be waiting for the wood to reach 6.2%
thanks,
Jeff

[David Gendron]

I think for a work bench, like Shwarz had said in is book, even if the wood is a little wet it's not a real problem... That said, and looking at what you gain in moisture drop in 2 weeks, an other 2 and it will be close anough. Do you have some air exchange/ movement where the wood is sitting? add a fan or even better a dehumidifier, and you will speed up the process!
Keep us updated

[michael osadchuk]

I have recently purchased a bunch of doug-fir to build a workbench and am waiting for it to dry.
According to the current FWW based on the current temp (70 degrees in my garage) and the relative-humidity (30%) I should expect the wood to reach equilibrium at at 6.2%.
Is this true?
In the past 2 weeks the driest of the wood has fallen from about 14% down to 12% (some of the wood was over 20%).
At this rate it will take weeks to fall to 6.2%.
I realize this is for a workbench but want to do things the right way so I am really curious if I should be waiting for the wood to reach 6.2%
thanks,
Jeff

Regarding the first question about whether FWW's figure of 6.2% is correct: another way to check wood has been dried/acclimatized to your specific environment is to just do a moisture meter check on an piece of wood that has been in your workshop for a couple of years or more and that is of approximately the same density as the doug-fir; the moisture content reading of that acclimatized wood is about what you want your doug fir to ideally dry to.

good luck

michael

[Bob Smalser]

Also remember most glues require wood to be under 12%. Resorcinol allows as high as 15%, and poly glues 19%, although the wetter the wood, the weaker the poly bond.

[Gary Herrmann]

I wouldn't think you could get air dried wood down to 6%.

[David Gendron]

You sure can, I have quite a bit of it!!

[Steve Thomas]

If your at 12 pc go for it. Kilns have trouble getting timber to 6 pc. To go from 12 pc to 6 pc all the way through the timber, not just on the surface will take months / year.

[John Keeton]

You sure can, I have quite a bit of it!!

Jeff, as David noted, air dried wood can get pretty dry! I recently pulled a piece of 6"x8" red oak from the barn. It was stored wet 5 years ago. I metered it during a relatively damp period for us during the winter (probably 60% RH outside), and it was 7.2%. During the year that will vary. Over a period of 2-3 weeks of dry weather, I would think 6% would be expected.

But, the point really is to take into account the shrinkage that you are undoubtedly going to get. Just use good construction technique, and you should be fine at 12% for a bench. I would prefer drier wood for cabinet grade work.

You may experience problems when you attempt a joint with opposing radial/tangential shrinkage factors - a dovetail with the grain running QS on one board vs. flat sawn on the other. The shrinkage could result in a tightening or loosening joint depending on circumstances. One always has some of that, but at 12%, it deserves a little more planning.

Consistency also plays a role, and if some of the wood is 12%, and some is 16%, then that could create other problems. You want it all to move together.

Just my thoughts - others may disagree.

[Chris Friesen]

I'd go for it, but with some caveats:

1) Assume the top will shrink a bit in width and in thickness. If you want the front flush with the legs then attach it in such a way as to force all movement to the back edge.
2) If possible use the wetter stock for the pieces with mortises, and the dryer stock for pieces that will be tennoned.
3) Drawbore your main stretcher joints (or use bolts) so that they stay tight (or can be tightened) as the legs shrink.
4) Plan on flattening the top again once the wood is fully dry.

[James Scheffler]

based on the current temp (70 degrees in my garage)

Oh, sure. Rub it in. Today is a warm day in MA and it's up to 31 F.

David - what's it doing up in the Yukon?

Jim

[David Gendron]

Jim, up here,it's almost summer right now, snowing and about 29F. A beautiful Day!

[Mark Roderick]

Personally, I think it would be unwise to build the bench before the wood has dried as much as it's going to dry in your shop.

A 24" piece of Douglas Fir (the width of the bench) drying from 12% to 6% will shrink about a quarter inch radially and half an inch tangentially. Of course you're not going to use a 24" piece of wood, but even with smaller pieces you're going to experience some cupping and twisting as the bench dries.

To me, building a piece that's guarantied to move in the three months after you build it is much more frustrating than waiting for the wood to fully acclimate to the environment.

[Chen-Tin Tsai]

This is going to sound like a dumb question, but how do you actually go about measuring what the moisture content in the wood is? Is that just surfact moisture, or all through the wood? Also, is there a rule of thumb to figure out what the moisture of a given piece of wood should be before working with it?

[David Gendron]

CT, you can use a moisture metre, or you can weight the wood and determin that way when the wood is at equilibrium, that is when the wood doesn't loose weight any more.
As for the moisture content of the wood to be worked with, as long as it got stable with the environement, equilibrated with your shop, it shouldn't mather wich is the moisture content. So rule of thumb, is to let the wood in your shop for a couple weeks before working with it. It as to be stickered. And of course, that doesn't apply to green wood!