I am wondering, what is the best way to stack 4x8 sheets of plywood? Also, are there any tricks I can use to flatten some cabinet shelves that have bowed/warped?
From contributor R:
I do not think that it is possible to flatten bowed or warped plywood. I once had a couple of sheets of 3/4" red oak plywood that were badly bowed. I lightly moistened them on both sides and then lay them on the bottom of a stack of 40 sheets of 3/4 melamine.
Although I always knew they were there, I left them on the bottom of the pile for nearly 10 years (of course the stack of melamine would sometimes dwindle down to a couple of sheets but it would get replenished promptly). Then one day I needed to pull those sheets of oak plywood when I ran short on a job. Those sheets quickly sprang back to their original bowed state in a matter of minutes. I think that a plywood straightener can only be purchased from the same outfit that sells board stretchers.
When you store your panels flat, you need to make sure that you have a cover sheet on top - this well help to maintain equal moisture on both sides of the panel. Otherwise it will cup/bow. It will shrink to the side that has less moisture (dry side). Think of it as shriveling up.
Introducing moisture to this side or removing moisture from the other side will help to correct this. Putting it on the grass in the sun will both introduce moisture and remove it. This is not always the cause of warping, though. Sometimes the panels are not glued well, and there is not anything that you can do to change that.
There really isnít any solution except maybe moistening one side and working fast. This isnít any help if it's to be used as a refrigerator panel though. I have a piece of DF 3/4" ply about 22" x 66" that is over 40 years old. It's been used as a ramp, table-top on saw horses, and generally abused in every way short of using a flame-thrower on it Ė and it's perfectly flat.