Delivered a lift of kiln-dried Cumaru to a job site Monday, tarped it tight on the driveway, and by Friday half the top layer had cupped. I know now the tarp trapped ground moisture — lesson learned. Question is recovery: if I sticker-stack the cupped boards under shade with airflow, will they flatten back out, or are the worst ones firewood? About 20 boards with 1/8"+ cup across 5-1/2".
Sticker-stack them cup-DOWN with weight on top, shade and airflow, and give it 10-14 days. In my experience about 80% come back flat enough to use. The ones over 3/16" cup usually don't fully recover — rip those for stair nosing stock.
Also fasten the recovered ones with screws not clips — they'll want to move again and clips won't hold a board with memory.
Hey there, Sorry to hear about the cupping—I've been there too. Stickering those boards is definitely the right move. Make sure to space them out enough to allow for good airflow; ideally, use 1-inch stickers. Keep them out of the direct sun to prevent further twisting and ensure you're in a shaded area. You might also want to apply a wood conditioner like Titebond III or a similar product after flattening, just to help stabilize them. In my experience, if they’re not too severe, you can salvage quite a few. Good luck! Cheers, Sam Whitfield
Bummer on the Cumaru. Since they're only cupped at 1/8 inch, you've got a solid chance. After you get them stickered and shaded, throw some weight on that top layer—stack scrap plywood or even a few cinder blocks across the boards. It forces them to flatten as they re-acclimate. Just be careful with humidity swings; if it's super humid, it might take a week or two. Once they flatten, seal those end-cuts immediately with Anchorseal or a similar wax emulsion to stop moisture ingress through the ends, which is usually where this nightmare starts. Don't write off those boards just yet.
Sign in to join the conversation.