I recently glued up some new boards, and after planing and trimming, I left them outside to sand. Unfortunately, I stepped out for a few hours, and when I got back, they had all warped. I understand now that I should have kept them indoors to prevent the heat from causing this issue. I'm trying to figure out the best method to uncup them. I've put some heavy weights on top, which has helped a bit, but there's still some bow left. I'd rather not replane them if there's a way to fix this without losing too much material.
3 Answers
When boards dry unevenly, one side shrinks while the other doesn't, causing them to cup. I suggest bringing them indoors—it often helps them straighten out over time. Just keep them in a stable environment with even humidity.
I've had some luck with a technique involving a towel and water. You lightly spray the cupped side with water, then place it face down on a towel and let it sit. It helps even out the moisture. Just keep in mind, it’s a bit finicky and may not always work perfectly. I managed to reduce a half-inch cup to less than 1/8 inch with this method. Check out this video I found for more info!
Just a heads up, cupped boards are different from bowed ones. Cupping is across the grain and a bit trickier to fix. If you're trying to flatten a cupped board, sometimes screwing it down while applying pressure can work, depending on what you're using it for.
Thanks for clarifying! I definitely have cupped boards.
Installed a c-channel afterward to keep any more cupping from happening!