How to Straighten Warped Plywood
I thought that the whole point of plywood was that it couldn’t warp, but I have some that has done just that. Is this a manufacturing defect? If not, is there anything I can do to correct the problem or work around it?
Marc Alfant, Melbourne, FL
The belief that plywood doesn’t warp is common, but mistaken. Even if the sheet is flat when you buy it, it often will cup or twist in your shop. But unless it is intended for a spot where it won’t be fastened down, like an adjustable shelf, you can still use it.
Here are a few tips: If the warped piece will be the top of a cabinet, put the crown on top. It’s better than having a top that sags. Face the crown in on the sides of a cabinet, as the shelves will push it out.
A sturdy back and a face frame also will help take out the warp. A biscuit joiner will place biscuits evenly along the edge of a curved panel, pulling it into line with a straight row of biscuit slots in the back of the frame. If you absolutely need flat sheet goods for your project, use something with a medium-density fiberboard core.
Build smart to overcome warped panels
Plywood isn’t always flat, but if you point the crown in the right direction and use a back rabbeted into the carcase, you can straighten all but the most severely warped parts.