Bowed plywood. Will it eventually flatten out?

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Forum topic by noone posted 05-23-2012 03:01 AM 15438 views 0 times favorited 8 replies Add to Favorites Watch
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05-23-2012 03:01 AM

I have a few sheets of 3/4” and 1/2” birch plywood that is stored upright at about a 10 degree angle. Over about 3 months, it has bowed from leaning against the wall. I cut up the 1/2” ply to try to make a crosscut sled and discovered that over 48”, when laying flat, the left and right side are bowed up about 3/8”. Obviously this won’t work too well for a crosscut sled base. Is it possible that if I lay all this ply flat that it will flatten out? The ply is stored in a humid Florida garage. I don’t know if it matters, but I did flip the remaining plywood sheets around hoping they will bow back to flat. I’ll probably end up taking the mused sheets back to the Depot once I can get access to a pickup truck anyways, but I’d still like to know how others in humid climates deal with bowed (expensive) plywood.

8 replies so far

View Scot's profile


344 posts in 3571 days

#1 posted 05-23-2012 04:35 AM

You can work the bow out by putting stickers under each end and putting a little weight in the middle. Just be careful not to bow it the other way!

-- If the old masters had power tools, they would have used them. So get off your damn High Horse.

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583 posts in 2448 days

#2 posted 05-23-2012 02:07 PM

“stickers under each end”

Not following here…... ??

Are you saying to flip it over and then have the bow facing upward and then put some weight on it to flatten it out?

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1730 posts in 3244 days

#3 posted 05-23-2012 02:23 PM

I try to buy only what I need for a project, but there’s always some that must be stored. I store my sheet goods on end with the long dimension vertical, and with as little angle as I can get without it falling. When I get some bowing, I just reverse the lean and it goes away in a day or two.

You mentioned Home Depot and expensive plywood in the same sentence. Hopefully, you know that HD plywood is anything but expensive – or very good quality. I have some ply remnants that are left over from sheets costing over $100. – lol

-- Adversity doesn't build reveals it.

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1642 posts in 3159 days

#4 posted 05-23-2012 02:47 PM

I live in an area that gets a lot of humidity changes and at times can be quite humid as well. So I try to buy only when needed, but being a wood hoarder of sorts I do end up with extra sometimes. What I do if I have 2-3 sheets I need to store. I sandwich them between 2 sheets of OSB and clamp them together with cauls and c-clamps. The OSB keeps the humidity from directly coming in contact with the plywood sides, and by clamping everything together helps to keep the plywood as flat and untwisted as possible until needed.

Your question, Are you saying to flip it over and then have the bow facing upward and then put some weight on it to flatten it out?

Yes, generally I set a gallon of paint in the middle and allow the humidity to straighten out the sheet naturally. That’s why you want to put stickers (stickers are equal size strips of wood to allow for air circulation between layers)under the sheet at the ends and I put a couple in the middle to prevent over flatting the sheet.

-- I don't make mistakes, I have great learning lessons, Greg

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583 posts in 2448 days

#5 posted 05-23-2012 02:54 PM

I thought that $45/per sheet for plywood was relatively expensive…... But yes, I now realize that sheets such as Baltic Birch are more solid and more expensive.

So for example, I now have a 48” by 27” piece of bowed ply that i’d sure love to flatten out to use on my crosscut sled. Maybe it will just flatten out by itself in a few weeks?? Hopefully…....

I guess the good thing about the Depot is that I can return anything over any period of time and get full store credit for it for the current going price. And it’s accessible. I don’t know of any place near me, other than Woodcraft where I can buy wood, but i’d sure like to know.

I’m in Jacksonville, FL.

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5032 posts in 4069 days

#6 posted 05-23-2012 03:13 PM

I try not to store plywood on the concrete floor………it will wick moisture up into it which is never good. Like the others said, sticker it, allowing air to flow evenly around it.

3/8” over 4 ‘ wouldnt concern me unless it was going to be cut into a door, and I would never use plywood for a door as it is prone to warping under ideal conditions. It’s a guess that after you cut the parts, and then join one part to another, the warp will likely disappear.


-- "Good artists borrow, great artists steal”…..Picasso

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583 posts in 2448 days

#7 posted 05-23-2012 03:16 PM

It’s 3/8” over 24”. Over 4 ft, the left side end sticks up 3/8” and the right side end sticks up 3/8”. With the middle laying flat.

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583 posts in 2448 days

#8 posted 05-23-2012 03:45 PM

When you store your plywood, do you make maybe 12” lengths of 2×4’s and make a ladder to store it on?

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