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I have a consistent problem with warped sheet goods, particularly plywood and MDF. They always seem flat when I buy them, but by the time I use them they are always curved or twisted. It's a source of constant frustration. Even 3/4" stuff gets a slight curve.

The way I've always stored everything is simply to lean piles of it against a wall. I don't have a lot of space.

After a recent comments discussion it dawned on me that this might be the problem:

Totally off topic, but how did the MDF warp in the first place? I have this problem where none of my MDF stays straight, and it frustrates me because all I hear about is how stable MDF is. – Jason C

The piece was stored vertically and had leaned a bit in the storage rack causing a slight twist. – Ashlar

My question is: Could this be my problem? Can storing these sheets vertically be causing all the warping?

If so, is there a way to store sheet goods vertically without damaging them? I don't have the space to stack them horizontally.

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  • In case you missed it at the time, more storage options at the bottom of my Answer here. – Graphus Jun 14 '16 at 7:09
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MDF is heavy and we all know that. Like keshlam says if it is not supported across its vertical span then it will pull itself down slowly warping it. Gravity is a [w]itch.

Now if you cannot store it perfectly vertical then you are not out of options. I couldn't imagine the space needed for some larger sheets however you should be able to get away from perfect verticals as long as you support it. A half a-frame comes to mind in an effort to take up less space. Idea being to discourage as much movement as possible. I could hang onto wood for years until I know what I am doing with it. This should be an efficient use of near vertical space. Depending on design you could hide boards inside the frame as well if you are not up to wasting space.

Half a-frame

Image from Orange County Crating

Lean the sheet but brace it as much as possible so as to not allow movement. I suppose if you are worried about the edges, which can damage easily, then you could put down some cloth along the bottom to cushion it.

Depending on the size of your sheets this might not be realistic though. Laying it flat also comes to mind but that is not something most workshops can entertain.

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    The face of that frame could also be made to act as a poor man's panel saw, with a circ saw and a T-square saw guide, giving you something of a twofer in that space... I think... – keshlam Mar 6 '16 at 19:33
  • Yeah. That would be a good idea as well. – Matt Mar 6 '16 at 19:35
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    That frame is the only way really to do the job. One extra point though - to keep it properly flat, you need something to hold it flush against the back of the frame. Ratchet ties over wooden battens will do the job perfectly well. This also ensures the sheets don't fall on top of anyone if they knock the frame. Another point on that frame is that the lower rim of the frame (where the sheets sit) should be perpendicular to the back, otherwise the edge of the sheet will be dented by the weight of the sheet. – Graham Mar 7 '16 at 12:49
  • Adding to @Graham, each sheet of material has to be flat against the sheet behind it. If the sheet is supported only at its bottom edge and top edge, it will eventually sag. – Ast Pace Mar 9 '16 at 5:40
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If you lean stuff against a wall at an angle, it's weight will tend to cause it to bow. If you can stand it fully upright with support on both sides that will be less likely to happen.

Or you can figure out a way to support it lower down, so the middle can't sag.

Or, of course, you can lay it flat if you have space to do so (most folks don't).

Or delay buying until you're ready to use it, so it doesn't have time to pick up a bend.

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  • Another possible safeguard: multiple sheets strapped/clamped together at top/middle/bottom will tend to protect each other – keshlam Mar 11 '16 at 12:26
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Moisture can add to this problem. Do not let the wood come in contact with cement or concrete block. They will need to be supported in the back and possibly held down in the front. Even when stored horizontal they can warp if moisture is present. In the lumber yard they come in banded together but a few day after they cut the bands the top sheets may start to warp.

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What I do with sheet-ware due to lack of space, is basically "hang them on a wall". I built a heavily braced and supported shelf low down, with a row of holes perpedicular to the wall every 60cm (~2ft). Then the same up top, with the rows of holes, but individual braces instead of a continuous shelf, with some old sliders (what I had on hand) so the top braces can move vertically.

How it works, is I put the sheets "on the shelf", pack them as tightly against the wall as I can. Then I put broom handles/shafts down the holes closest to the sheets, and then slide the top braces down so the top end of those broom handles go in the corresponding holes up top, gently tapping them down with a rubber mallet.

This way, the sheets are stored "perfectly" vertical, without any room to bow, not contacting the concrete floor. And braced on both sides; by the wall on one side, the broom handles on the other. I drilled the holes in a 2x side-by-side staggered pattern to give me finer "adjustment" of the broom handle braces, but whenever no hole lines up ideally vs the thickness of the sheet stack, I slide a handful of wooden wedges in between the broom handles and sheet stack, to close the gap.

I built the bottom as a shelf, to enable crate storage underneath. But it could also just be some thick wood on the floor, as long as it acommodates the holes, lifts the sheets off the floor, and is anchored so it doesn't slide away from the wall when bracing. This obviously won't be ideal for large (really thick) stacks, or very heavy material - but within common sense I've found this solution to work very well for my use.

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    Wow, that sounds... serious! Please add a picture or two. I think I've got a pretty good idea of what you've done, but pics would be idea. Welcome to Woodworking - great first answer! – FreeMan Dec 5 '20 at 14:20
  • That's a neat idea, if I'm visualizing it correctly. Do you ever have problems with it becoming a "booby trap" where things get iffy when you pull out the broom handles? – Jason C Dec 6 '20 at 21:47
  • Actually now that I think about it I just did something similar for lightweight sheet materials (my collection of glass and acrylic); in my hallway I built narrow "shelves" with a tiny lip; screwed an eye hook into a stud a few feet above each one near the center; and I just secure everything with a bungee cord between the eye hook and the shelf. It works really well. I never really thought to extend it to larger, heavier materials - the broom sticks + slides are a great idea. That'd be perfect here. – Jason C Dec 6 '20 at 21:50
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The answer by user1981 probably has the key.

The top and bottom sheets will warp cause just one side is sealed and the other is exposed to air. Air exposure will allow it to take on or shed moisture depending on atmospheric conditions. The side snugged up to the next sheet gets no contact with the air so the moisture content of the sheet is imbalanced and causes warp.

Note that all the sheets in the middle remain flat so store vertical and use spacers between sheets just like sticker boards when drying fresh sawn lumber.

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