Plywood Question

[havighurst]

Last year I cut some plywood to the rough dimensions, but I never had time to finish my project. I went out today to continue my project and found my plywood has bowed, not much, but enough to effect my project. Is there a way to flatten it out?

Thanks

[cabinetman]

You may have some luck overbending in the opposite direction. It may take some time, check it often.
.

[Slik Geek]

How thick is the plywood?

[Mr__Bill]

I have tried to warp ply back to flat. Bending in the other direction and holding it there for a few weeks helped some but it still had a bow in it. I have set it out in the sun with the convex side up and watched as it flattened and then bowed in the other direction. Taken inside that night it reversed it's self. I have set the concave side on the damp concrete with a weight on it and had it mildew on the bottom and still be bowed.

My neighbor is with the local mill that makes plywood. He tells me that when manufactured if the press is not right when the glue is dried there are stresses in the ply. CDX is manufactured fast and warping is not an issue with sheeting so it will often warp as a full sheet and when still banded in a unit. "A" grade and hardwood ply some care is taken to get the pressure and temp right when making it but it's not a perfect thing and moisture change in a piece of ply will change things enough so that it warps. Even just cutting it can change the stress and cause the resulting pieces to warp. To get ply that doesn't warp you need to buy ply that was made with some care and the face and core ply are compatible. The produce must also have been taken care of in transport and storage. What you want to buy is ply that is not too young and has been stored flat and dry, preferably some that is about half way down the unit and several months to a few years old. The closest thing to flat the local mill makes is MDO and it tends to stay flat. It is a good choice where the finished piece will be painted.

If you ever get your pieces back to flat you may wish to get a sealer on them and then sacrifice a few chickens to the wood gods of warp.

Bill

[JimD]

For most projects, I fasten one piece of plywood to another and push them into alignment as I am fastening them together. Even when they were not very flat before being fastened together, the resulting projects have been fine.

Jim