A.Paul Fisette, director of the Building Materials and Wood Technology program at the University of Massachusetts in Amherst, responds: This is a difficult thing to do and there’s no guarantee that it will work, but sometimes you succeed or at least improve the situation. When a piece of wood bows, the convex surface of the "arc" is longer than the concave surface. To correct this, you must equalize the surface lengths. First, wet the concave side with water from a spray bottle. Then, clamp the door flat. Put the door on a flat surface — a wide workbench is best — so that the door cups upward. Cut lengths of 2x4 and place them across the door along the bowed edges to pin the door between the strips and the flat work surface. Don’t fully tighten the clamps right away — this should be a gradual process. The next day, spray the same surface again and tighten the clamps a little more. Play this out until you think the door is as flat as it will get. Let the door dry thoroughly, then seal all surfaces and edges.
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