This article is intended to illustrate how to “straighten” warped plywood. We all know that when we go to the hobby shop and pull the appropriate thickness of Midwest or other brand aircraft plywood that it will be warped (the thicker stuff is not as susceptible to warp).

OK, so how do we fix it? It’s pretty easy if you think ahead a little. Suppose you need a ¼” thick fin, so normally you would purchase a ¼” piece of aircraft grade plywood, trace and cut your pieces, right? That would work, but now the fins are slightly warped.

Instead of doing that, take your desired fin thickness and divide by two. Then gather the following items together:

Many large, heavy books of any type from your home library, maybe a few free weights from your personal gym, or that 20lb bag of lead shot from the gun store that you use for noseweight in your rockets.

Here’s the procedure:

  1. A Formica countertop is the best place to perform this procedure, as it is flat, dense, with no irregularities.
  2. Cover your work surface with waxed paper; this will keep the epoxy off of the countertop possibly saving you from the wrath of your wife, or parents, or other authority figure.
  3. Place the two pieces of warped plywood on the work surface with their concave sides facing up towards you, so that they rock like a rocking chair.
  4. Mix an appropriate sized batch of epoxy; remember that you don’t need much because this is a lamination project.
  5. Apply a VERY THIN coat of epoxy to BOTH sheets of plywood, on the concave side of each sheet ONLY (the sides facing up).
  6. Take one sheet and flip it over so that it’s wet side faces the wet side of the other sheet.
  7. Lay out some waxed paper on top of the assembly so that it overlaps by at least an inch or two all around the edges of the plywood. This will keep the books clean.
  8. Push down on the two pieces, applying great pressure with your hands, and hold the piece together. Align the corners as best as possible for a square assembly.
  9. Immediately place a large book on top of the assembly, and heavy books (or weights) on top of the large one until the assembly has cured.
  10. Occasionally check the corners during curing to make sure that both pieces are square in reference to one another, sometimes they squish out of alignment.
  11. After curing, remove the books and waxed paper, trace your fin patterns and cut away!

I use this technique on all of my scratch built projects, and it works well. I have even put fiberglass cloth between the two pieces to stiffen/strengthen the assembly. I don’t know if it really did any good, as I have not empirically tested it, but it appears to have worked.

Submitted by: Jon H. Ruehle