Dehumidification drying wood questions....

you should have bought a fan

Bill Tindall, E.Tn.

Wood contains water in three "places". There is liquid water in the vessels. You don't need environmental modification to get this water out. In fact you don't want to remove this water faster than it can diffuse and wick to the surface. Good air circulation is helpful to prevent staining. Large operations either stack lumber outside for this step or inside "leaky structures with fans.

There is water in the cells. A lot of this water will come out just by bathing the wood in ambient air. When this water comes out the cells shrink and the lumber shrinks. It is at this step where warp, check and all the bad things happen. Kiln operations highly control moisture loss at this stage. Hasten this step and bad things are worsened.

Finally there is water bound to the lignin and cellulose. You need to have low humidity to remove this water, achieved either by heating the air or dehumidifying. It will be a while before you get to this step.

Re: Dehumidification drying wood questions....

TomD

The key to drying in the small shop is to forget about it. I usually have something in mind for the green wood I get, but whether it gets used for that purpose or not is another mater entirely. If you are trying to rush this to get to the fun bit of making you bed, that can end in tears.

Most of the splitting tends to occur in the early part of the drying, or with the first exposure to direct sunlight. If you have pith centers, they almost always split, in my experience, so ripping them is often a good idea.

I have had great results coating the ends of the wood with Bear UltraWhite indoor outdoor paint. As good as using the emulsion, better than some of the emulsion I had from a turning place, so all emulsion is not equal. I just find the paint is easier to stock and has so many other uses. It needs to be good quality paint, I have used stuff that made no difference, and the wood cracked.

I would imagine the dehumidifier would work. You could put the wood in a tent of sorts with the dehumidifier, and run the drain hose to the outside. Get a tarp, or something of the sort for the tent.

I usually finish up with the wood in the living area where it gets to sit for a year or so. Stick it under a bed or sofa, if you can get away with it. Not worth it if it subsequently spends months in your shop at a different moisture content.

I have no experience with the particular wood you are drying.

Re: you should have bought a fan

Barry Irby

I was buying stuff at a huge tool auction. There were the most fantastic tools I have ever seen in a home basement shop. For example, a Hammer K3 table saw with the giant slide assembly big enough to rip or cross cut a sheet of polywood and a 10" jet cabinet saw. Floor model jet hollow chisel mortiser, 36" drum sander, two Carvewright machines, and on and on, 211 items.

What I wanted was his shed full of wood, but alas, it went for too much money. I bought a few smaller things like a Leigh dovetail jig and a Porter cable dovetail jig, both to resell. And several other things, but the dehumidifiers were an impulse purchase. At less than $20 each, I grabbed them. Just thought they might be useful.

Thanks for the primer on drying. I knew most of it but got in a hurry. I want the wood to dry so I can finish the bed or what ever while I'm still alive.

The ends are sealed

Re: Dehumidification drying wood questions....

Barry Irby

Right now the ends are sealed with stretch wrap. I did not want paint or emulsion on them so I wrapped the tightly with multiple layer so shrink wrap. I have some excellent paint and may use that.

I think your advice to forget about it is good. I forget about a lot of things lately, but usually not on purpose. I am staring down the tunnel of mortality and suspect I am about to get hit by a train. I have worked myself up into a state of wanting to get things done before it's too late and while I still can.

I just went a looked at these pieces and they have lost twenty pounds in three weeks. It seems there should be a way to work out what an acceptable dry weight would be, by starting when they are wet and calculating what the weight loss would have to be.

Re: you should have bought a fan

Bill Tindall, E.Tn.

Keep air moving over them for now. In the summer put them where it gets hot like an attic or loft and they will be fine by fall. Or rig the dehumidification somehow. 25% to 10 is where bad stuff happens

16% to 8% is what is hard to accomplish without lowering humidity by heat or dehumidification.

From my limited experience with firewood, red gum dries about like poplar....easy. The interlocked grain will make you wish you never owned it when it comes time to work it. .

Re: Dehumidification drying wood questions....

David Weaver

Shrink wrap in the long term for some woods may lead to fungus or other things that you don't want. If you're going to lose the ends, anyway, it may not matter, but I've had wet maple get nasty quickly (wood that got wet, but had been dried originally) and I didn't know that it was wet for almost a week. Within a very short period of time, the green filth growing on it went very deep, and I ended up having to bleach the wood to recover it.

I grew up in a stingy area, and we had a local mill, so folks who still built buildings back then with hardwoods usually hauled trees to the mill and then brought them home to dry or store. "barn paint" was what I recall seeing on board ends, but don't know why. Maybe the local miller recommended it - in theory, back then, it would've been an oily paint intended to work well on weathered and not perfectly prepared wood, but it could've just been cheap.

Re: Dehumidification drying wood questions....

Barry Irby

I have wrapped about three inches of each end.

I think they will dry without mold.

Wonder if the paint they recommenced was lead based. the lead would have been a good fungicide if nothing else. Back in the day farmers painted barns with paint made of linseed oil and red lead powder. Cheapest paint around.

Re: Dehumidification drying wood questions....

David Weaver

This was in the late 70s and early 80 - of course, some lead paint was still around, but I recall that it was 1978 or so that it went off of the market.

I was curious enough about oil based barn paint to go look, and some do say that they have linseed oil or other oils designed to work well with weathered wood, as well as fungicides.

I always thought it was just cheap. I must admit that I haven't used any common oil based exterior or interior paint since July 1995...coincidentally, painting a barn.

(the current really cheap "barn and fence" stuff is flat latex red and probably really is just junk).

Solar kiln...

JL

Make a smaller solar kiln.

And just use a fan.

Use something like the Suntuf roof panels (Home Depot).

The best setup I've seen had the translucent fiberglass? panels.

It had an exhaust fan (bathroom style) set in the side w/ a timer (or maybe a humidistat).

You could open the door in the side to load/unload lumber in the rack.

The roof had maybe a 12/12 pitch.

Anyway, you could load and unload w/ relative ease.

red barns

Bill Tindall, E.Tn.

The (all, most, some?) red barns were pigmented with red iron oxide mined near Clinton, NY. Red lead (lead oxide) paint was used as a protective coating on steel. Barns too? White Lead (lead carbonate) was used as pigment in white paint.

Re: red barns....An Aside

Barry Irby

When I first got out of college I was hired as an assistant supervisor for a commercial contractor. Much of my work involved laying out walls and other things on slabs and forms. We used red lead powder in string line chalk boxes instead of red chalk. The lead would stayed in place resisting rain and wear. Spent days with my hands coated in read lead powder. Wonder what the health consequences were?

I live in red clay country. Is it true that it's iron oxide that makes clay red?

Re: Solar kiln...

Barry Irby

I see a number of small saw millers on YouTube that have solar kilns, most of them based on a design by Va Tech. I have considered setting up such a kiln.

I have a green house attached to my house for the purpose of gaining some heat. I have considered using that. I need to kick myself into gear.

An Aside

Bill Tindall, E.Tn.

Spent days with my hands coated in read lead powder. Wonder what the health consequences were? We see them every day (you walked right into that one)

While red lead is insoluble in water it dissolves readily in hydrochloric acid.....like what is in your stomach.

Is it true that it's iron oxide that makes clay red? yes

Red and white barns...

David Weaver

...that pretty much covers the barn colors where I grew up, at least as far as barns of appreciable size.

There were certainly either unpainted (or treated?) wood barns that were brown, but i can't say for sure they were never painted.

I was going to mention earlier that some barns were white (the one that I had to paint on a ladder with a brush - the guy employing me just thought a brush was a better way to paint than anything else - block/stone foundation (probably partially rebuilt) and white wood. Painting unpainted stone and block with a brush is slow going.

One of my relatives soaked everything in creosote, so he had a lot of outdoor woodwork that was black/brown. he died last year of neuroblastoma (but also was a prolific TV repair man - lots of exposure to things that are known unhealthy).

Re: Which is Preferred?

William Duffield

"See Rock City"

or "Chew Mail Pouch"

?

I tried dehumidifier method without success *LINK*

Keith Newton

Barry, I had read an article in FWW many years ago that seemed reasonable, but when I tried it, I wasn't able to make it work after trying two units for a couple of weeks. That's when I pulled the second dehumidifier out and replaced it with a small space heater blowing in air from the outside while letting some air escape from the enclosed space. It was a pretty large stack of red oak, but only took a couple of weeks to get down to about 6~8% from air dried.

Think of this like your clothes dryer. It draws in air from the outside, over the heating elements into the drum, letting the hot moist air escape. If you just turn the heat off so it only pulls the outside air through, it's going to take a LONG TIME. The warmer the air, the more moisture it can absorb, and the quicker your lumber will dry. As long as there is some moisture evaporating from the wood, the temperature will be lower and go up slowly. When the wood is finally dry, I've had the temp go as high as 150º which is more than enough to kill any insects as well.

I hope the pallet manufactures in your area don't find out your cheating them out of their skid materials. They might be out to get you if they do. ;-)


http://www.woodcentral.com/cgi-bin/readarticle.pl?dir=newarticles&file=articles_946.shtml

dehumidifier will dry lumber, but

Bill Tindall, E.Tn.

The equilibrium moisture content of wood depends on the relative humidity. Lower RH by any means, equilibrate wood to this RH and eventually it will dry. Arizona for example.

There are two problems with the dehumidifier approach. The air coming out of the unit is cold and 100% RH. Unless there is some means of heating this air before it gets to the lumber stack the lumber stack will approach the temperate of the exit air and equilibrate at 100% RH.

And.....the diffusion rate of moisture out of lumber is highly temperature dependent. Without heat, equilibration will take a long time.

Bottom line....as you describe, dehumidification without external heating will not work.

Re: dehumidifier will dry lumber, but

Barry Irby

Interesting.... I have zero experience with dehumidifiers and did not know the air from them was cold. As I said, i bought them on an impulse because they were cheap, less than $20 each. My understanding is they are an air conditioner that cools air enough to dehumidify it and then dumps both the dehumidified air and the exhaust back into the space, so there is a net heat gain. Oh well, I have spent more money on dumber stuff.

The wood is drying rapidly and getting some interesting ripples. I may sand it and let it continue to dry and see what happens. I suspect these head boards may look like something that Fred Flintstone might have had.

Re: Bill, the air from Dehumidifiers is warmed!

Larry Clinton At Frankfort, (Central) Indiana

Not saying your statement is wrong as far as drying wood, but the air exiting the units is warmer than the room air. The normal "compressor style" works similar to an air conditioner except an air conditioner cools the compressed Freon in the evaporator coils by use of the finned radiator and the heat is blown outside. The Dehumidifier cools evaporator coils by blowing the cold dried air across them and into the room as warm dry air.

However as you stated the temperature of the exiting dried air may not be high enough to quickly dry the wood near as well as elevating the temperature.

Re: Bill, the air from Dehumidifiers is warmed!

Keith Newton

Larry, I'm sure there is the air is a little warmer coming out the back end of a dehumidifier , but whether it is from pumping a fluid through the tubing is beyond my pay grade. However I'm sure there is some heat generated by running the compressor though. Now, the question is whether it is more efficient to heat the air with a compressor, or the element in a space heater?

I have some doubt about whether those compressors would last when the temperature rises to 140º.

In the method I described I don't worry about taking the moisture out of the air, but rather just let the same amount of air escape that is being blown in under my tarp bubble. The escaping air takes the moisture along with it.

more discussion

Bill Tindall, E.Tn.

You are correct in your discussion. I failed to consider that this is how people were using the dehumidifier. (though I now see that this seems to be a reasonable way if one had never dried lumber before).

I presumed one would run a lumber dehumidifier in a home environment by pulling in room air, passing through the unit and exhausting dehumidified air out the back and into the lumber environment, like a commercial dehumidification kiln..........The commercial unit then heats this exhausted air, dropping its relative humidity to near zero and upping the diffusion rate of moisture out of the lumber. I think Keith runs his drying this way, and , it works as expected.

Mine works by pulling in room air, passing the air over a chilled coil to condense moisture and then exhaust freezing cold air to the room, or lumber pile.

This dehumidified exhaust is joined by warm air from the compressor when used to dehumidify a room. The net thermodynamics is to warm the total from work done by the compressor and fan. Indeed if the unit was sealed in the enclosure with the lumber, there would be a small net rise in temperature. But, this mode of operation will never get the net humidity low enough to dry the lumber to 7% MC and the rate will be glacial. I doubt the drying rate from this way of operation would be as great as just blowing ambient air through the pile with fans. Until the lumber gets to around 25% moisture content moving air through the pile at a good clip is the fastest way to dry.

Poplar dries readily. When we air dried poplar in the summer, if there was a breeze through the stacks the exiting air would be cold from evaporation.