Ironing Plywood

A cabinetmaker has success straightening out bowed plywood with a hot iron. December 28, 2005

In another thread, we discussed the fact that I was building a European style kitchen and most of the work required flat true panels. I was curious about moisture entering the thin face veneers and making the plywood bend one way or another. I now have a pair of doors, cut from the same sheet side by side so the grain patterns match, and one door curves out and one curves in. I started thinking about the moisture issue and took my iron and applied heat to the concave side and after about 4 passes it had straightened out, and now I have to see if it will last. If you need to straighten your plywood out, use your wife's iron - just don't let her know you're using it or you will be buying her a new one like I had to. I will let you know whether or not it stays straight.

Forum Responses
(Cabinetmaking Forum)
From contributor A:
It is interesting that drying out the hollow or concave side would straighten the bow. The concave side of a bow is usually the dry side. Did you use steam? My experience is opposite in that placing the convex side of a panel to face the wood stove will cause it to reverse bow. Now that you have an iron in the shop, the next time you get a dent in unfinished wood you can steam it out by placing a wet piece of clean cotton cloth between the dent and the hot iron.

From the original questioner:
To contributor A: You're right, I should have said the convex side. I dried the convex side so that it would shrink and pull itself straight. I wouldn't want to add moisture with steaming it - that could only spell trouble when it came time to finish it. So far it has held (3 hours). Now I need to do the other one to make them meet nicely. I'll see what it looks like tomorrow.

From Gene Wengert, technical advisor Sawing and Drying Forum:
Be careful applying heat and steam to veneers as sometimes the adhesive will soften and even melt away. We can always bend wood using heat and moisture, so once it is straight, hold it so it will stay straight as it dries. Bend it straight. In fact, bend it very slightly in the wrong direction, as when you release the pressure it may spring slightly.