Steam-drying wood

[dstreck]

The planking stock for my current build is still too wet (4/4 flitch-sawn AWC currently at about 25% MC or so). My final plank thickness will be 3/8", and I'm planning on despiling onto full thickness stock and resawing to get two bookmatched planks. The garboard and first broad need to be steamed to take the twist at the hood end. I know that steaming dries wood out, but how much? My hope is that it will drive the MC down to closer to 15% or so, thus killing 2 birds with one stone. Pipe dream? Any idea how long you have to cook 3/8" cedar at 210 degrees to bring it down to acceptable MC?

Thanks in advance for any advice.

[rnb1016]

try splashing on a liberal application of kerosene with a little linseed oil mixed in, let that soak in over night then steam, that should drive out a considerable amount of moisture.
good luck. maybe some pictures of finished project?


also 1 hour of steaming per inch of thickness is the general rule, so 20 minutes or so should do it.

[dstreck]

Kero/LO sounds like a good idea. I think I'm gonna steam a test piece and put it on the moisture meter after it comes out. Its a lapstrake build, and as its a spare time project, I'm guessing only a strake a week will go on. Since its only 3/8" stock, hopefully each successive strake will dry a bit before the following is hung. I guess we'll see.

[seo]

If you have a moisture tester on hand, it would be easy to do a test run with, say, six samples, all cut from the same plank, put in the steam box together, then one sample taken out at ten, another at twenty, and so on, and see what the moisture content.
I'd be very curious to see how much your plank width and thickness change from wet to cooked.

[S B]

The ceramic industry has the same drying stress problems as the wooden one. It is common practise to force dry ware,by heating it to 100C, at 100% humidity and moving it to a cold dry environment. The escaping heat takes the water with it in a dramatic fashion. No reason to think the process would not work for other materials.

[bloggs68]

Your first couple of planks will probably have a good bit of twist in them so the bit of extra moisture in there to help transfer the heat will allow them to bend easier.

If you are worried about being too wet, just re-saw them now and it would only take a little while for the timber to dry at that thickness. You can still save some time by cutting out one plank and clamping it to the second board to get an identical strake. By the time you got to the planks that don't require steaming - at least at a part time building rate, the planks would be dry enough. Just don't dry it too quickly.

There is always plenty of other things to go on with - spars, oars etc.

regards,

AD

[Bob Smalser]

Pipe dream?



Pipe dream. Most of the water is inside thick cell walls and none of the methods mentioned will remove it.

Stack them vertically inside the house behind doors and whatnot and wait. Or find a local kiln and have your planking stock brought down to 15-19%.

The problem with partially-seasoned stock isn't so much shrinkage as the banana peeling you'll get when you rip or resaw a plank that's dry on the outside and sopping wet on the inside.

[dstreck]

Roger that, Bob. Thanks.

[S B]

Pipe dream. Most of the water is inside thick cell walls and none of the methods mentioned will remove it.

Stack them vertically inside the house behind doors and whatnot and wait. Or find a local kiln and have your planking stock brought down to 15-19%.
I take it you have tried all these ideas and from your experience you know they don't work. How exactly is it, you think a kiln works?

[Bob Smalser]

1) I take it you have tried all these ideas and from your experience you know they don't work.

2) How exactly is it, do you think a kiln works?



1) Actually, yes. Even the kerosene. And several more, too. For example, packing wood in rock salt works great to speed drying, but is kinda hard on fasteners later. Shortcuts always have costs. And the more poorly-informed the shortcut, the greater the cost.

2) "Kilns" don't dry at all at 100% humidity and 212 degrees F. Steam stages where used are to kill bugs and set colors. Notice below how much time it takes in one typical kiln schedule to bring 4/4 cedar from green to dry and stable. Around seven, 24-hour days. Disregarding the excellent chance of ruining the stock with too much heat for too long, do you really think an hour or three in the home steambox will put even a small dent in the moisture problem?




http://www.fpl.fs.fed.us/documnts/usda/ah188/chapter07.pdf

USDA Kiln Schedule #HC, 4/4 Light Cedar

Step #....Time in Hours....Dry Bulb Temp.....Wet Bulb Temp

1....0-24.....130F....123F
2....24-48...135F....125F
3....48-72...140F....125F
4....72-96...150F....135F
5... 98-120...155F....135F
6....120-144...160F...135F
7....144-168...160F...140F



One advantage of geezerhood is the distance between me and the turnip truck, but by all means feel free to repeat my mistakes.

[seo]

What's "banana peeling?" Shaky?
On an almost entirely unrelated subject, in 1978 I had an interesting conversation with Doug Lee, the owner of the North End Shipyard, Rockland, Maine. He was at the time getting ready to build a 90' lod schooner (The Heritage) for his passenger business. I asked him if would kiln-dry the 8/4+ red oak planking, and he said no, it would make it too hard to fit. Besides, he said, the wood would be underwater for the rest of its life, so why take high moisture wood, dry it to low moisture, and then make it high moisture again.
I think they sawed all the planking stock out of the same forest, at the same time, and it's likely that the planking used above the waterline had some time to air dry a little while the below-waterline stuff was being put on. In any event, the "Heritage" is thirty years old now, and looks pretty good.

I've wondered about another question too. If the principal behind steam bending is that wood becomes pliable based on its temperature, then the steam is just a convenient way to heat the wood with a built-in upper temperature limit of 212ºF.
Heating higher than 212 might be bad for the wood because of generating steam pressure inside the wood's cell structure?
But maybe it's good to heat the wood to bending temperature all through the piece. In that case, maybe steaming high-moisture wood is better, because the dry wood is a better insulator, so the interior of the wood might heat faster.

This might be an advantage, because it seems to be true that wood that's been in the steambox too long becomes kind of "dead," less springy, more prone to breaking. The only reason I can think of for that is that some part of the structure is damaged.
I base that idea on what I observed why working for my brother making shaker-style ladder-back chairs. The ladder-back slats with about 5/16" thick, cherry or black walnut, steamed and then bent over a form, then finish-sanded after drying, and assembled.
Shaker chairs built old-fashioned are very light structures, and flex a lot under load. It's important that the slats be "lively," and my observation was that if a slat was steamed too long it became more "deadly" than "lively."
In an attempt to quantify this, and while away a winter evening, I built a very simple test block with a 1" deep mortise in it. The cooled slats were tested by putting an end into the mortise, and test-bending it, and twisting it as well, then putting the other end in and testing again. As I remember the idea was to flex it about 2" over a 14" length, and twist maybe 15º both ways. The result was a failure rate of about one in ten, which saved time in finishing slats that would be thrown away later.
All this did was confirm what was apparent just by picking the slat up and giving it a tweak. A piece that was going to break in the tester felt different.
From this process I developed an idea that kiln-dried wood was maybe harder to steam and have it come out lively. But there were a lot of variables, and no control on where the wood came from, etc. I can imagine the test process that would quantify this, by taking boards from the same log, bending some green, bending some KD, and then some air-dried. It's not entirely clear who would be interested in the results. Or if it would be re-inventing the wheel.

[S B]

1) Actually, yes. Even the kerosene. And several more, too. For example, packing wood in rock salt works great to speed drying, but is kinda hard on fasteners later. Shortcuts always have costs. And the more poorly-informed the shortcut, the greater the cost.

2) "Kilns" don't dry at all at 100% humidity and 212 degrees F. Steam stages where used are to kill bugs and set colors. Notice below how much time it takes in one typical kiln schedule to bring 4/4 cedar from green to dry and stable. Around seven, 24-hour days. Disregarding the excellent chance of ruining the stock with too much heat for too long, do you really think an hour or three in the home steambox will put even a small dent in the moisture problem?



One advantage of geezerhood is the distance between me and the turnip truck, but by all means feel free to repeat my mistakes.
Of course there is no drying at 100% humidity, that is why this environment is chosen for the heat introduction.There is no chance of accidental and uneven drying. Drying takesplace at the cooling stage.

[rnb1016]

just for clarification, the kero/l.o. treatment was a suggestion taken directly from the text of an article by Capt. R.D. "Pete" Culler, who by all accounts is one of the foremost builder/designers of wooden boats. His work is akin to artistry and I wouldn't hesitate to try a tecnique that he advises.