They're usually made in such a way
as they shouldn't warp under normal circumstances.

These doors warp if they get damp. Full stop. They're designed to go to 12%
moisture (and have been taken to 18% in the lab) without warping - and
that's not very damp at all. If you've been using the bath or shower, the
air on the corridor side of the door may have reached 20%+. There's no known
cure.
In short, immediately paint 'em on 6 sides (like it says on the
instructions!), or they warp!


Steve Almond

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It's not what you know, it's what you know about who you know