Moisture in air dried wood - Woodworking Talk - Woodworkers Forum
 
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post #1 of 15 Old 10-06-2008, 03:54 PM Thread Starter
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Moisture in air dried wood

I'm air-drying red oak in my basement using two dehumidifiers and a fan. Here in NE Ohio the outside air humidity is now ~40%. Through the summer, (to smooth out the electrical bill) I set the dehumidifiers to shut off when the humidity fell below 65%. Now I've re-set that to 55%. Since they still operate, I figure the wood is still contributing moisture to the air.

My moisture meter is pinless (Wagner). When the wood was fresh cut, the meter read 32%. I compared it to finished wood furniture --6-9% and some white oak (from a lumber yard) -- 8-10%.

Today, my new lumber has been drying for only a couple months, and is already down to 15% (at least on the top boards). I'm in no hurry to use it before it's ready, but I have some questions:

- Is that rate of drying believable? (Seems fast to me)
- Is the moisture meter accuracy the same for furniture and new lumber?
- Is the moisture in that white oak too high to build furniture with?
- If the white oak only gets down to 10%, what moisture content am I really going to be able to get on the red oak? (When is it ready to use?)

Last edited by David K; 10-06-2008 at 03:58 PM.
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post #2 of 15 Old 10-06-2008, 04:59 PM
 
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You didn't say exactly when you started drying the lumber. How thick is this lumber? Are you also using fans? It's a myth that it takes 1 year per 1" thickness to achieve EMC. But there are many factors that affect drying. It does seem fast for 4/4 oak but it may have been from a log that had been down for a while and the lumber started dryer than lumber from a freshly-felled tree.

The accuracy of moisture meters can be subjective. I think I heard that none of then can measure moisture contents above 33%. Checking by weight is the best method.

15% is too high to build most furniture designs.

You can achieve 7-10% by air drying indoors in a controlled environment. But this may be hard to do in a basement. You might try constructing an enclosure around the stack and putting the dehumidifier in it. This is typically done using nothing more than plastic sheeting.
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post #3 of 15 Old 10-06-2008, 05:20 PM
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Air Drying will never be furniture wood

I know this may start a war, but from what I remember from way back when, Air drying will only get the wood down to about 12 to 15% under fairly good conditions at that 1" per year rate.
Here is what I know, which may be old news, but here goes:
There are two types of water/moisture in wood. I cant remember the technical terms so I will describe as best as I can.
First there is the free water, This is the water that is inside the cells or tubes that actually move the water from the ground up to the leaves in a tree. This is the water that dries up fairly rapidly with air drying. This will bring the moisture eventually down to 12 to 15%.
Secondly, there is the bound water. This is the water that is trapped in the cell walls that make up these tubes. This water is very difficult to get rid of and will most likely need to be kiln dried to get it down to the 6 - 8% moisture content for furniture use. This is what is considered stable enough for household furniture.
Keep in mind, that when I say the wood will never get down to that level by air drying. I don't mean for that to be taken literally. It would just take too long to describe all of the conditions that could make it happen in a normal house.
Next, my percentages may be slightly off, this is only the best I can recall from 20 years ago. Sorry.

I hope someone here can clear this all up one way or another from actual experience with details. Theories change as time passes because more things get documented.

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post #4 of 15 Old 10-06-2008, 05:28 PM Thread Starter
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The live trees were felled in February, ends sealed with Woodcraft's green wood sealer, and sawing done in July. It is 4/4.

It's in a walk-out basement and the gas boiler is in the same area. I am using fans, too. The space is big (15' x 80'), so I might be trying to dehumidify NE Ohio. Even if I am, though, it's rapid drying that surprises me here, not slow. With the yard-bought white oak at 8-10%, I wonder whether that's moisture added by local humidity, or never removed at the kiln. If that moisture came from the air, then how could I hope to get the red oak below that? I sure don't want to use this wood at 15%, but can I use it at 10%? (I read the goal is 7%)

The plastic idea sounds interesting. I imagine it will cut down demand for dehumidifier power.
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post #5 of 15 Old 10-06-2008, 07:18 PM
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Quote:
Originally Posted by Tony B View Post
I know this may start a war, but from what I remember from way back when, Air drying will only get the wood down to about 12 to 15% under fairly good conditions at that 1" per year rate.
I hope you're wrong about air dried wood not making furniture wood. That's mostly what I've been using for years. I hope it doesn't all explode with a splash tomorrow.

Actually, you're right that air dried wood will never get moisture levels as low as kiln dried, but I don't think it matters. I'm currious if furniture builders had any special techniques for drying wood 200 years ago.
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post #6 of 15 Old 10-06-2008, 07:38 PM
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Originally Posted by dirtclod View Post

You can achieve 7-10% by air drying indoors in a controlled environment. But this may be hard to do in a basement. You might try constructing an enclosure around the stack and putting the dehumidifier in it. This is typically done using nothing more than plastic sheeting.
That would work. You are not really air drying David since you are using mechanical assistance, air drying is in a shed/stacked out doors.

There are many questions in this thread, I will try to hit the high points (I need a shower) Yes kiln dried wood that was 7% can get back up to 10% as it reaches EMC (equilibrium moisture content), so you probably bought dry wood.

200 years ago they dried in the attic for one, that works as a kiln. With proper joinery furniture can still be built with air dried wood. Some areas if the country wood actually air dries to 7% (arid southwest).

White oak dries much slower than red. No your rates are not too fast. I dry oak in 3 weeks in my DH kiln. I air dried 4/4 oak/cherry/walnut/honeylocust...from fresh sawn to below 15% in 100 days +/- in my shed over the summer.

I have built plenty of furniture from air dried wood (11%-12% in Illinois) and dragged it in the house. It is all about joinery.

I am late to get someplace and am filthy. I will not be back till much later this evening if at all. I am sure I missed some stuff, but the advice you are getting seems sound to me.
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post #7 of 15 Old 10-06-2008, 09:54 PM
 
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I haven't tried it but you can achieve 7-8% in many attics. Air drying outdoors will range from 10(?) to ~17%. In the loft of a barn may get you 10%. Finishing it off in a conditioned space like a home (not basement) or shop might also get you 10%.

I've heard the same as Daren about the old methods. I've also heard of using a fire under elevated stacks of wood outdoors. I can't remember where I heard it but I remember the author saying it was still being practice in his neighborhood in Tennessee. I have no idea how it was set up so it wouldn't catch fire.

The goal is to make the wood dry enough that, after manufacture, it won't move much acclimating to the EMC of the end location. Going to 6-7% is more than enough when it's typically going to end up at maybe 10% in a conditioned Midwest home, or 7% in a Southwest home.
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post #8 of 15 Old 10-07-2008, 09:54 AM
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Originally Posted by Geoguy View Post
I hope you're wrong about air dried wood not . I hope it doesn't all explode with a splash tomorrow.
I'm currious if furniture builders had any special techniques for drying wood 200 years ago.
For one thing, as Daren noted, 200 years ago wood was dried in lofts in barns and attics. The temps there and the air flow would be not too different than a kiln. Also note that 200 years ago, there was no such thing as dehumidifiers, modern heating systems and air conditioning and therefore the wood would not have to be dried to as low a standard as today.
And finally, I used to collect antiques as well as refinish. Most antiques that were 'living' in a barn or shed were not cracked and separating. Once put indoors, they would slowly dry out and and joints would separate. By antiques, I am referring to furniture built over a hundred years ago. So, no your furniture wont explode, but it might come loose at joints or possibly crack. All depends on the moisture content of the wood and inside your home. You may also get lucky and have no ill effects.
Usually country style furniture doesn't show these effects because of design and some of these effects are actually desirable. Not so in modern and contemporary designs.
Just because something might show negative effects doesn't necessarily mean it will, unless of course you apply Murphy's Law, which always applies to me.
I'm sure if your furniture is not showing any ill effects after 2 years or so, it probably never will.

Tony B

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Last edited by Tony B; 10-07-2008 at 10:02 AM.
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post #9 of 15 Old 10-07-2008, 11:58 AM
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Very informative thread guys, learning a lot here.

Daren, since we live in the same general part of the country, what would you expect the end EMC to be for air dried only in a barn loft, assuming the proper use of stickers, airflow and woods native to our area?
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post #10 of 15 Old 10-07-2008, 12:55 PM
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Hi David

I have found that wood will air dry, with a fan blowing over it, down to about 12 to 15 percent in my unheated shop. Wood in our home is about 6 to 7 percent. When I want to build something I will plane out the boards, and then bring them into the house to finish drying before final planing and assembly.

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post #11 of 15 Old 10-07-2008, 01:15 PM
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Originally Posted by Tweegs View Post
Daren, since we live in the same general part of the country, what would you expect the end EMC to be for air dried only in a barn loft, assuming the proper use of stickers, airflow and woods native to our area?
I would expect the wood to dry to 10-12%. EMC is always changing. Here is a little more reading for everyone.

http://www.forestprod.org/cdromdemo/wd/wd4.html

http://www.csgnetwork.com/emctablecalc.html

The problem can come in when wood that has never been drier than say 12% is used to build furniture with tight joinery. That furniture is brought in to the house and all winter the furnace is running and the relative humidity in the house is 30% and the temperature is 70 degrees...the wood will want to dry to just over 6%. This makes the wood shrink.

Here is some reading on shrinkage. http://www.woodbin.com/ref/wood/shrinkage.htm
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post #12 of 15 Old 10-07-2008, 04:35 PM
 
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Allmost everything you wanted to know about air drying lumber: http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr117.pdf#

That's a large document. But estimated drying times by thickness, specie and geographic location are found on pages 14, 23, 24, 25 & 26.
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post #13 of 15 Old 01-06-2009, 08:03 AM
 
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Ah, the old air drying vs kiln drying debate. One thing rarely mentioned about kilns is that the wood doesn't stay in them. It comes out, gets stored, goes to a lumberyard, gets stored, gets sold, gets stored. Kiln dried moisture contents are only immediately after the wood comes out of the kiln. After that it takes on the moisture content of the environment it's in. So air dried wood and kiln dried wood stored in the same place will reach the same moisture content. My shop is heated. So my air dried wood reaches heated indoor moisture content after some time in the shop. The same moisture content as the kiln dried wood that's in there. How you dry is not what determines moisture content. It's the environment the wood is in that determines ultimate moisture content. If I bring kiln dried wood into my shop in the summer when the humidity is high, it will gain moisture until it's the same as the air dried wood that's in there. Kiln drying is for speed, not for ultimate moisture content. And that moisture content changes with the seasons. That's why joinery must take into account the seasonal change in moisture content, whether the wood was air dried or kiln dried.
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post #14 of 15 Old 01-07-2009, 11:16 PM Thread Starter
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Here's an update of what's happened since July '08, when I was just starting to dry red oak in my basement. I'm near Cleveland, Ohio. In February 2008 we had to take down three red oak trees that hung over the house. I painted the ends with Woodcraft's end sealer. They laid in the yard on 'sleepers' made out of branches until being cut into boards.

The guy who owns the WoodMizer did the work in bits and pieces. Weather and better-paying jobs meant the logs were sawed in some months, but not others. In November the last were cut.

Everything was stickered and stacked on 3/4" strips of white oak (knotty pieces good for nothing else). Wood was stacked on the same day as cut, and now there are two piles, 6' tall. Each is 4' wide, with lengths from 8'-13'. It took some re-stacking to keep longest boards on the bottom. I guess there's 2500-2800 BdFt there.

Through the summer, the two dehumidifiers worked almost constantly. Two fans kept up a good breeze. The whole basement smelled like vinegar, but never moldy. When weather turned colder, the dehumidifiers (set to shut off at 45%) began to run less often. We had 'sweating' on the single-pane glass windows, and dampness on the concrete sill under them, but no other signs of water. The plaster ceiling shows no sign of changes.

Now it's January, and the surfaces I can reach are reading 15% - 18% on a pinless Wagner meter. I see only 3 boards with checking, up to 6" on one end.

What SC said makes sense. The lumber I bought at a yard two years ago is reading 8-9%, up a bit as it's stacked in the same room as the new wood. I imagine in time the new wood will get to the same level.

The project has been fun, but I wouldn't have done it if I weren't taking down 80-year old oaks from my own yard, and I couldn't have done it if I didn't have more basement than I need. I think in the end, I'm going to figure out a way to have these milled into flooring. I don't know any other way I'm going to use 2500 BdFt of oak, and I really would rather keep seeing this particular wood around the house.

Many thanks to you all for the advice!
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post #15 of 15 Old 01-08-2009, 11:02 AM
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Hi David

I hope you save some of that oak for furniture. Don't forget that after you have your oak milled into flooring you will want to stack it in the house, stickered, and preferably in the rooms where it is going to lay, to let it acclimatize to the humidity in the house. The longer you can leave it, the better.
If you have 2500 bdft you are one lucky dude.

Gerry
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