Wood Movement: How Big a Risk?

      In principle, solid wood joinery that does not allow for wood movement is a recipe for disaster. In practice, sometimes you get away with it. June 18, 2009

Question
I was watching one of our employees build a side-job recently out of oak. He's not a furniture maker, he is apparently our hired know-it-all and tells everyone how they should do their work (micromanager). He's the one that knows more than you do about any aspect of woodworking and has learned all that there is about it, and you aren't as good as he is.

He built a large desk looking hybrid thing out of solid oak, and built the carcass just fine. But the doors are a different story. I've never in my life seen anyone build a door like this. It basically looks like a 5-part door, except it's all glued together into a 1-part slab. What he did was glue/biscuit a handful of 2" oak planks together tall, and then glued another 2" plank running across the top/bottom covering the end grain and completed the door by putting another couple of 2" strips on the sides. In other words, like a 5-part door but the middle panel is not dadoed in, it's biscuit/glued in and all sanded to a flat slab. The doors are about 15" square. I kindly said to him that in time some of the glue joints might fail when the vertical planks in the center expand. He matter-of-factly reminded me that the biscuits in it would stop any such thing from happening. Perhaps I should have saved my breath? They look very nice. I wonder how long that will last.

Forum Responses
(Furniture Making Forum)
From contributor G:
If he is in a controlled environment, AC in the summer and humidity added in the winter, there is a good chance they might not fail. I have a table top I built that way, 18" wide and 42" long out of curly soft maple and 4 years later it is still whole with no separation of joints.



From the original questioner:
For his sake I hope that's the case for him. The piece will be sitting in an air-conditioned office.


From contributor R:
You should leave one of the doors out in the grass over-night then have a company meeting about rule number one in woodworking: wood moves. This should put your guy back in his place.


From contributor G:
It is bad woodworking practice, but you can get away with it on pieces smaller than 20" or so. I wouldn't do it with a softwood, they seem to expand and contract more with humidity than hardwoods. Also, the better you seal it the more chance it has of not failing. Not something I would do for a client. But when I made my table I did it in 11 hours. That was from the first cut to the last coat of finish.


From contributor A:
We have all done this a few times. Sometimes you get away with it and sometimes you don't. Other times you scratch your head have another beer, bitch at your boss or yourself for being an idiot and try not to do it again in case it does blowup at a later date. Why rock the boat? It will be his failure unless he blames you for his poor choices.


From contributor G:
Also, if he built it in the prime of summer, when everything was at its most expanded level, then it is likely to survive. If he built it in the dead of winter then it would likely fail.


From contributor K:
Over 25 years ago I built four cabinet doors with tongue and groove bread board ends out of reclaimed pine. I glued the whole end approximately 14 inches long. These doors are as solid today as then, no cracks or splits. On the other hand four years ago I built three lap desks the same way about the same size. Two out of three of these split. Go figure, I assume it was the moisture content that created the problem and prevented it also.


From contributor N:
The time before it fails depends on the starting MC. If it was far from the EMC, it won't be long.


From Gene Wengert, forum technical advisor:
I second contributor N's comments and add that a rapid change in MC is worse than a slow change. So, if the finish is very effective in slowing moisture vapor moving into or out of the piece, it is possible to survive. But, in most cases, with high MC in the summer, but low RH and EMC in the wintertime, and with standard finishes, the piece will try and shrink across the grain (not along the grain). This will create stress and potentially some failures.



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