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post #1 of 9 (permalink) Old 03-09-2010, 08:07 PM Thread Starter
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Default Plywood warps

Hi Ho: Am currently building a miter bench with drawers etc. and have run into a problem with plywood that is warped. Since it was in a stack about 3 or 4 feet high at Home Depot I assume it was straight when I got it but it is now warped about 1/4 inch over 3 feet. It was stored on edge which is not ideal, but I have an idea that it was probably not completely dry when I got it a couple of weeks ago. This is good quality 3/4 inch plywood in the sense that there are no voids and the surface is cabinet quality.

Has anyone else run into warped plywood and has anyone found a way to make it flat again?

Thank, Dirk
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post #2 of 9 (permalink) Old 03-09-2010, 09:13 PM
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One trick that might work but not always is during the day lay it out on the grass. Something about the moisture from the grass & the heat of the sun will straighten it out. I've only had that work one time for me. So now I store material to avoid the problem in the future.

James
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post #3 of 9 (permalink) Old 03-09-2010, 09:30 PM
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Originally Posted by dirko View Post
...make it flat again?
Hopefully you have a little time before you need to use the ply... one thing you can do is to clamp straight 2x4s to both sides of the top and bottom edges, then hang/suspend the clamped ply vertically from the ceiling till it dries evenly on both sides.
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post #4 of 9 (permalink) Old 03-10-2010, 10:04 AM
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What are the dimensions of the bench?
What's stopping you from adding intermediate material, (stud) to fix and flatten the ply to?

All things sag under its own weight, often the spacers under the stacks of material at the lumb. yd. aren't evenly placed or there may be dips in the pavement it sits on. Thus the material sags to even out load.

If both faces of the sht. are clear count the number of plys, 7 and less is construction grade. The only truly voidless ply I'm aware of is marine grade.

If both faces of the sht. aren't clear you may have AC, it has voids, they may not show up at the perimeter.

Underlayment can have 1 good side and the other plugged, it has voids but they're very small 1/4" or less in diameter and -0- and still warp. Both are and can be used in flooring and construction and don't require perfect flat

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post #5 of 9 (permalink) Old 03-10-2010, 08:01 PM
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As others have mentioned, if you can store it in a weighted or clamped situation, you may get it back to flat. One thing I know about Home Depot is that they have now discontinued sheet goods from the Far` East. Too many complaints. Last week, at my local HD stores, most of the sheet goods was made in Chile, go figure.

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post #6 of 9 (permalink) Old 03-10-2010, 08:11 PM
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As others have mentioned, if you can store it in a weighted or clamped situation, you may get it back to flat. One thing I know about Home Depot is that they have now discontinued sheet goods from the Far` East. Too many complaints. Last week, at my local HD stores, most of the sheet goods was made in Chile, go figure.
Well now the prices might go up after the damage there. They make a lot of MDF there too.

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post #7 of 9 (permalink) Old 03-10-2010, 08:20 PM
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Hi Dirk

I don't see the big deal, once you cut it up the screws and glue will pull it back flat..

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Hi Ho: Am currently building a miter bench with drawers etc. and have run into a problem with plywood that is warped. Since it was in a stack about 3 or 4 feet high at Home Depot I assume it was straight when I got it but it is now warped about 1/4 inch over 3 feet. It was stored on edge which is not ideal, but I have an idea that it was probably not completely dry when I got it a couple of weeks ago. This is good quality 3/4 inch plywood in the sense that there are no voids and the surface is cabinet quality.

Has anyone else run into warped plywood and has anyone found a way to make it flat again?

Thank, Dirk



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post #8 of 9 (permalink) Old 03-14-2010, 02:43 PM Thread Starter
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Hi Ho: Thanks for the response. This plywood looks good on the stack. There is one good face and no voids. The problem is that pieces about 28 by 39 inches form drawer supports, and while the top and back are held in place the front is open for drawers. Since these pieces hold slides they must be spaced properly for the drawers to operate properly.

Anyway, I have never had plywood warp as much as this has. Even CDX and ordinary AC plywood doesn't.

I will weight the remaining sheets and hope it gets better. I can work around the warp, but it is a real hassle. Would wetting it and weighting it down in a stack or clamping it work? I don't know whether it has external glue or not, so I am a little hesitant to wet it.

Dirk
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post #9 of 9 (permalink) Old 03-14-2010, 03:09 PM
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Would wetting it and weighting it down in a stack or clamping it work? I don't know whether it has external glue or not, so I am a little hesitant to wet it.
Hi Dirk, 1/4" over 3' really isn't that bad... and as BobJ said, once you screw it together, it'll pull together fine... just maybe a little tricky for milling.

In the future, if it's possible, store it flat and covered so as to keep the moisture equal on both sides. You said that the ply is in good shape structurally, so that leaves one side of the ply dryer/wetter than the other side, which will make it warp.

No, don't add water! You are wanting to dry it equally on both sides to remove the warp.

For a quick fix on a sunny day what you can do is to lay the ply on the grass with the bowed side up for a bit. Moisture from the grass will slightly wetten the bottom side and sun will dry the top side, temporarily un-warp the board, but wood is always seeking an equalibrium, so eventually it'll return till it's dry on both sides. That's why I recommended that you clamp and suspend it on the third post of this tread...

Last edited by anotherBob; 03-14-2010 at 03:47 PM. Reason: errant bly...
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