I am a mostly hand-tool woodworker with modest resources – these include working in a thin-walled garden shed with a propane heater going when I’m in there in the Seattle winter. In general, I work on projects from wood that is stored year-round in the shed, finish them usually with polyurethane, and then move the completed furniture into our (centrally-heated) house for use. I have noticed that joints which were planed/sanded flush, and finished to a smooth surface appear to shrink across the grain after a few weeks inside to the point that the surface of the joint is no longer flush, and a ‘step’ can easily be felt between individual components. I assume this must mean some partial fracture of the glue line, and compromise of the joint. In one case a lap joint that was precisely cut, clamped and glued, and finished with polyurethane, began to frankly split. I assume all this has to do with moving wood from a relatively wet environment (my shed) to a dry one (our house), with consequent drying out of the wood, despite finishing all surfaces with relatively impermeable polyurethane. How do I deal with this depressing problem without building a climate-controlled workshop?? Should I keep my wood in the house and only work it in the shed? Would a dehumidifier help? There must be plenty of others in my situation working in a shed or garage without heat. Thanks so much
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Replies
If you need to work lumber that is wetter than the environment you need to make special provisions for wood movement in the construction. Lap joints are out--as you discovered, the same goes for miter joints. That also means you need to take care about such details as avoiding quarter sawn wood joining to plain sawn, since, as you found the plain sawn moves much more than the quarter sawn.
No finish will do more than slow moisture transfer--wood will achieve it's equilibrium level finish or no, though finish does slow the process and may help wood avoid the wide seasonal swings. But your problem is different you know it starts wet and will end up considerably drier. By the way, polyurethane varnish is not the most moisture impermeable finish material--shellac takes those honors.
I would make some efforts to keep your shop drier. Propane heaters could be among the worst since many varieties just dump lots of moisture into the air--if yours does this find a better heat source. You may find with Seattle's relatively low electricity rates that an electric heater makes sense. A dehumidifier may help. I'd also invest in a moisture meter so you can check moisture levels and compare moisture among your various lumber stocks.
>Should I keep my wood in the house and only work it in the shed?<
Yes.
I have a small limited shop area.
I store rough wood in the garage. The components that are machined to semi finished state wind up under the bed, behind the couch, under the couch . . . you get the picture.
In long term, as you are finding out, the protective coating you are applying does not stop wood movement.
I suppose you could finish and insulate your shop and heat it same as the house but I am getting out of my depth so I will shut up.
happy hand tool work
roc
The problem can also be caused by the glue line not shrinking when the surrounding wood does. You might try using poly glue -- it may not set up as brittle, but dunno, never tried it. Worth a shot tho'.
You left out one option - turn off the furnace in the house. ;-)
Seriously, when making furniture out of anything but ply or composites, you need to get the wood to the moisture content existing in the space where it will live. If that means keeping the wood in the house for a couple of weeks before, & during, the project, that's what you're gonna have to do.
Mike Hennessy
Pittsburgh, PA
Thanks all. For a start, I will try and improve conditions in the shed, and also keep project wood in the house for the most part - before and during construction, as much as possible. Appreciated.
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