Warping hardwood plywood.

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Forum topic by skatefriday posted 03-07-2015 01:24 AM 980 views 0 times favorited 8 replies Add to Favorites Watch
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415 posts in 1450 days

03-07-2015 01:24 AM

So last Sunday I cut down a 3/4” maple panel. The good stuff, B1 (sufficiently free
of defects for a carcass that is mostly hidden), combi-core, prefinished.
I finished cutting three pieces for a carcass for a medium sized base cabinet, closed up
the shop, leaving the panels stacked on my assembly table, and spent the week
doing the job that pays for the tools out in the garage.

It happened to rain for a few days. Shocker here in Southern California. I go out
there this evening to do the last cut to length on one of the panels and then
figure I can assemble it (pocket holes), and the top piece in the stack is U shaped.

All three are bowed to some extent. They’ll go in the scrap pile, but what I want
to know is do people just always cut and assemble immediately to prevent this?
Never cut if you live in an arid climate but know that your humidity is going to change
significantly because a few days rain is due?

At roughly $90 a panel, this stuff is too expensive to ruin. Must not make this mistake

8 replies so far

View fuigb's profile


475 posts in 2925 days

#1 posted 03-07-2015 03:20 AM

Never, ever have had 3/4 ply of any grade warp, and this is from the midwest where we have pretty wide seasonal variations in humidity. At 90 a sheet it doen’t sound like you began with crap, but the result suggests that the material must have been as wet as hell to move as you’ve described.

-- - Crud. Go tell your mother that I need a Band-aid.

View ajosephg's profile


1880 posts in 3528 days

#2 posted 03-07-2015 04:06 AM

I think I’d try letting them adjust to the humidity by stacking them with stickers between each sheet so that air can contact all surfaces.

-- Joe

View skatefriday's profile


415 posts in 1450 days

#3 posted 03-07-2015 04:09 AM

fuigb, I think the problem was our normally dry climate followed
by three days of much higher than normal humidity during our
abnormally rainy spell.

ajosephg, that was probably my problem. Not stickering the panels
that I had cut to size during our once-a-year rain event.

View AlaskaGuy's profile


4047 posts in 2276 days

#4 posted 03-07-2015 05:53 AM

Just like lumber plywood will warp with changes in moisture change.

Where I work we store a lot of plywood. It’s store flat in bundles and the top sheet is exposed to the environment on one side. Every time to go to the storage area to plywood the top sheet will be bowed. It curls upward because the exposed side changes MC.

Here’s a good discussion on why plywood warps.

-- Alaskan's for Global warming!

View skatefriday's profile


415 posts in 1450 days

#5 posted 03-07-2015 06:26 AM

AlaskaGuy, thanks, that’s exactly what I observed. Although I am just a guy
with a garage who buys his sheets one at a time. I have neither the storage
nor the money to buy truckload at a time.

View rwe2156's profile


2883 posts in 1448 days

#6 posted 03-07-2015 01:42 PM

Don’t throw it away just yet. Place it bow side up on a flat surface with a light shining on it and see what happens.

-- Everything is a prototype thats why its one of a kind!!

View Fred Hargis's profile

Fred Hargis

4954 posts in 2460 days

#7 posted 03-07-2015 02:54 PM

If that bow isn’t too bad, I’d just use it (in a cabinet carcase). Once glued into a box, it will do just fine…again, if the bow isn’t too severe.

-- Our village hasn't lost it's idiot, he was elected to congress.

View Ghidrah's profile


667 posts in 1189 days

#8 posted 03-07-2015 03:07 PM

It will also sag under its own weight if it supported at or near the edges and sits long enough. Coming back from that is rare.

-- I meant to do that!

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