Estes Equinox Build Part 11, Balsa Warping?

Backtrack: These pictures were taken a few steps before the sub fins were painted.
Some builders won't use the water based Elmer's Carpenters Wood Filler, or CWF. They say it warps balsa fins. Well, it does.

Here's the replacement sub fins for the Equinox jet tubes. They are only 1/16" thick.
One side of the fins got a brushed coat of CWF. The picture shows the curve after the CWF has dried on one side of the fin. The raised warp runs right down the grain line.

The other side of the fins also got a coat of CWF.
The second side counteracted the warp on the first side.
These two fins dried in the open air, not under a book or other weight.

The pictures at the right show the root and outside edges of the fins after sanding. The warp is gone!
Both fins are flat and ready to be glued on the jet tubes.