Moisture-Related Door Expansion

      It's not surprising for doors to "grow" when humidity increases. This thread offers some insights into the problem. January 26, 2009


Question
I made some cabinets for a stable a while back out of rustic hickory. I was back at the site saw the cabinets. The doors are inset with strap hinges mounted on the front. The problem is they expanded at least 3/16" each. They are pair of slab type doors 16" wide x 36" tall. I couldn't believe they overlapped at least 1/4". I will take them off and cut them down to fit again. The room is heated and has air conditioning and not sure how much they use it. Has anyone had this happen?

Forum Responses
(Cabinetmaking Forum)
From contributor L:
A solid wood slab door would be the worst culprit for expansion. If the woodshop and home/barn are not the same conditions you will experience shrinkage or expansion. The only problem with cutting the doors is when the dry weather comes along. You may now have unsightly gaps where they once overlapped. The best answer if you want to cut them is to make them very close, don't do your usual 3/32" gap. So when they shrink back up it won't be so large. Also, are they finished on all six sides. Oil doesn't count. They need to be sealed as best possible to minimize the expansion and contraction.



From contributor R:
Yes they were clear coated with three coats Precat. I was thinking maybe I should have made a lap joint where the center gap is?


From contributor J:
The amount of expansion you are seeing does not surprise me at all. Wood will expand as a percentage of its width. Doors of this type should be plywood with solid wood edgebanding, or do an overlay with mid stiles where the expansion will cause no problem.

Finishing the doors will slow the changes in dimension, but I don't feel it will stop it. I always have felt that if the material is exposed to the higher, or lower humidity, it will eventually change its dimension given enough time.



From Gene Wengert, forum technical advisor:
Are you saying that a 16" wide piece expanded by 3/16"? If so, that is 3/16" out of 256/16", so that is roughly 1% swelling. As a rule of thumb, a 4% MC change is 1% size change. So, do you know the RH right now? In an unheated stable, with occasional a/c operation, it would be about 55% RH is my guess.

Note: Without heat, this value will be the same all year. (If you check the weather records for almost the entire USA, you will find that the outside RH changes very little from winter to summer. It is not drier in the wintertime). So, I suspect that the doors are now 11% MC, which means that they were about 7% MC (35% RH) when you made them (a standard value).

The heat in the stable where the cabinets are located will dry the wood out during the heating season, perhaps back to 7% MC. If it is drier, the doors will shrink more than 3/16". You might consider a cleat on the back to "hold" the doors, but the cleat will only hold the back side and not the front, so then you will have warp and some overall swelling and shrinking too. Perhaps the best choice is to use an overlapping joint that has enough overlap to allow for expected movement.



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