WWA Info Exchange

I live in Minnesota and the relative humidity in my shop seems to stay somewhat higher than what is recommended for houses. This results in some of my projects warping quite a bit to the point that they end up as fireplace wood. Could this be a result of the way I machine the projects, am I doing anything incorrectly or is there a solution to this problem? I have been considering keeping the wood and project in my house and only moving into the shop as I work on a piece of wood? What do others do in this situation.

Thanks in advance

Hal Kossman

Hey Hal,
Acclimating the wood is always a good idea. You might also start taking a more critical look at the grain in the wood you choose. I would avoid plain sawn (face grain) and any rift sawn that is less than 60º I know that limits some of the character available for panels, but it's better than warping.

All that aside, the humidity here in Seattle is also pretty high; the problem is not really high humidity so much as changing humidity. So if you can manage the humidity in your home to be more uniform, you may have fewer problems.

Good luck,
Tom

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Mohandas K. Ghandi

You need to pay attention to the relative humidity. You can get hygrometers at a reasonable price to see what's in the house and in the shop. You want them equal, or close. Here's why. http://www.woodweb.com/knowledge_base/A ... ntent.html Though temperature plays a much smaller role than implied. The difference between, for instance human-friendly 60 and 80 F is at most a couple tenths of a percent at the same RH.

The business of avoiding flat sawn lumber is not as important as stated. Grade is a determining factor, in that knots and sapwood on the board can produce some creative shapes. This is because of differential in the grain pattern, but a quartered knot will still influence quartersawn wood. How the wood is sawed, otherwise, just influences the percentage of shrink. http://www.woodweb.com/knowledge_base/W ... rying.html Gives a few words and pictures. If you start with conditioned wood, however, and don't put it inside in front of a register or in sunlight, shouldn't be a problem.

If you want a good read, download at least chapter 4 from http://www.fpl.fs.fed.us/products/publi ... eader_id=p The first five chapters are great for understanding wood.

Species plays a role also. Walnut, for example, is inherently more stable than poplar. Joinery and finishing also influence this.

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I bring to life, I bring to death:
The spirit does but mean the breath:
I know no more. (Tennyson, In Memoriam)

Look for kiln dry wood @ 6%. a Dehumidifier in the shop will help. Store the stuff in your home for six months.
Its not easy to find good wood that you don't have to work the heck outta of it.
I like vertical grain for everything I build for my self but its not easy to find and cost money
I m starting to look for old barn wood. Something that was laying flat for years under a hay or something like .
I saw some old bleacher seats for sale years ago from the local school for cheap , I should have purchased some.
You can find wood all over the place that's dry really. Go to your local park @ night and take the picnic table maybe.
NO NO NO you cant do that
All kidding aside, I do like working with reclaimed wood. But you have to watch out for nails in the stuff.

Shrinkage does come with age.

Because the wood was once at X% MC doesn't mean much at all. It will re-equilibriate with its surroundings, swelling with additional, shrinking with less RH. While some boards may acquire some "set" in the process, you certainly cannot rely on it. Once again, the chapter in the free book covers hysteresis pretty well.

As to walnut being inherently more stable than poplar, you probably want to read the same chapter. Once wood has reached equilibrium, it's all pretty close in its response to changes. Differences tend to reflect density, though less dense woods with indistinct annual rings are more stable than denser woods with greater early/latewood differences. The percentages of shrinkage from green to bone dry do vary from species to species, but tulip-poplar - sometimes called yellow poplar ( Liriodendron tulipifera) - is virtually the same in volumetric shrinkage to walnut, though the ratio is a more common 2:1 tangential to radial, while walnut is 1.4:1. Still the choice of "poplar" for interiors, especially drawers, is a testimony to its stability once at 6-9% MC. My favorite for inners and unders, since tulip poplar doesn't grow around here, is bass. Its tangential to radial is 1.4:1 just as with walnut, and it is also very stable once cured, though it goes through considerably more volumetric shrinkage.

I did not ask my question as clearly as I should have. In Minnesota the Minnesota Department of Public Service recommends that the relative humidity in a house should be no more than 40% between 20 and 40 degrees, 35% between 10 and 20 degrees when it gets to 20 degrees below the relative humidity should be no more that 15%. I have a problem making something when the relative humidity is 40% and when the temperature drops to 10 or 20 below, warping is a serious problem. I recently made some 10" X10" walnut hot plates with decorative glass plates imbedded and they warped so much that a few if the plates broke and the others the plates no longer were flat to the wood. The question should have been "is there any thing I can do to prevent this warping?"

In my opinion, the simple answer is ... no. Consider that glass may change dimensions ever so slightly given a dramatic change in temperature, it will never, under ordinary circumstances, warp. A relatively flat piece of wood is bound to change shape in one way or the other depending on the grain orientation, etc., etc.

Given all that, the way I would approach such a project would be some sort of segmented glue-up where you could, to some degree, control shrinkage and expansion while limiting warpage. I'm not quite clear on what you mean by 'decorative plates' but assuming their enameled or otherwise opaque, I'd try using some sort of silicone adhesive, a rather heavy bond joint, to allow the wood to move independent of the glass. I've tried a number of projects incorporating brass and copper with wood with little success thus far due to the same issue: wood moves, other stuff don't. As much anyway.

I for one would really like to see a photo of your project(s), failed or otherwise. They sound very attractive.

[Edit: The subject line in the forum list shows a paper clip (attachment) but I don't see one. Is there a photo floating around in cyberspace somewhere I'm missing?]

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Cheers - Dennis

DennisS asked for a picture of what I am attempting to make. I attempted to upload two pictures, hope they work. The first picture contains one hot plates that did not warp and a tray that did. The warped tray had the insert decorative plate removed. The second picture is the warped tray with a flat object across the top to give an idea of the degree of warp. As you can see from the second picture the warping is over 1/2 inch across a 13 inch span. This is totally unacceptable for a flat tray. Hope this makes the problems I am having more clear.

Again thanks to everyone for the suggestions.

Hal Kossman

A little more info please.

Are you saying that when you take a completed finished project from your shop to your house it warps?

Is this Air or kiln dried?

Is it rough lumber that you are jointing and then planning yourself?

_________________
"To all those who work come moments of beauty unseen by the rest of the world." Norman Maclean

They're not doing you, or your woodworking any service. What they're doing is reminding you that warmed air is capable of carrying more water - absolute humidity - than cold. Cold air from outside raised to human comfortable can result in drastically low relative humidity, defined as a percentage of moisture in the air compared to what the air could hold at a given temperature.

Let the relative humidity get below 30% in your house and you facilitate drying of the nasal mucosa, which can aggravate other pulmonary conditions, and contribute to Upper Respiratory infections. Skin gets dry and itchy .... Doesn't do the furniture any good either.

I understand the health and comfort issues concerning relative humidity however if the relative humidity in a house goes to 40% when the temperature outside is below 0 or 10 below, moisture is a very serious problem and it can destroy the window wood moldings and form ice on the insulation, problems you do not want to experience. There does not seem to be a good solution to living in Minnesota, but I like it here.


In response to reelinron, the warping problem described occurs both with and without final finishing. Just made 6 trays and in the shop they looked very good before finishing. Finished the first with 6 coats of wipe on poly and was ready to give to my daughter. Taking it out of the shop, it warped to the extent that it broke the plate. The warping is as shown in the picture without a plate. Then took the unfinished trays out and after a day or so, they also warped. When returned to the shop after a day or so, they flatten nicely. I was told the walnut was kiln dried and it sat in my shop for 6 months or so. It was rough cut when purchased and I did joint and plan. However after jointing and planning, did not wait longer for more drying, immediately glued and worked the wood. Perhaps that might be part of the problem?

Thanks again for your thoughts and help
Hal Kossman

While I agree you don't want your windows sweating, a little moisture forming on the bottom of your windows on the coldest days should not cause a problem, that is from my experience in PA though.

As far as your warping, I use all Air Dried simply because I can get it cheaper from small little mills. I've had white oak that warped like a corkscrew when planed after being in my shop for a month, but worked fine after it sat for a year. It looked like it had been dried for a while but finally settled down. It was pretty straight grained too.

I wonder if the wood was kiln dried improperly. I would try again with a completely different batch of lumber, maybe even species.

If it keeps happening you may have to keep some wood in your house to acclimate and bring it back in the house while working with it like you suggested. That seems extreme to me though.

I have a shop at one of my schools that is below grade and is humid as heck in the summer. Next to the boiler room and gets bone dry in the winter and while I've had issues, never anything like you are describing.

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"To all those who work come moments of beauty unseen by the rest of the world." Norman Maclean

I'm above 46 north, so I do have some experience on this problem. If the house is not favorably laid out with heat directly below the windows, your use of curtains can give you condensation at night. The answer is to become more efficient overall by going to storms, windows, even a third layer of stretch plastic. Where you see the condensation, it's cold. Where it's cold costs you money.

I got some triple pane replacements when they were paying big rebates. When I shower, I get more condensation on the mirror than on the window. Furnace doesn't work as hard, either.

I'm really sorry, Hal, but still don't see any photos. Is anyone else seeing attachments?

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Nullum Gratuitum Prandium

Cheers - Dennis