During the build of my early 235, a couple of parts had to be molded (the
carb box upper and lower halves comes to mind - the factory-built parts came
along a bit later). Being an old model builder, I decided to carve the mold
out of a block balsa - it's really easy to work with, cuts and sands to
shape quickly.

The mold release I used was common duct tape, which releases quite readily -
at least with the Saf-T-Poxy II used then for wet lay-ups. The duct tape is
slightly flexible and of course, sticks to the mold like......well, duct
tape. You can smooth it out by merely rubbing it down and in fact, a
somewhat porous mold allows any air trapped under the tape to go away by
merely letting it be absorbed. If bubbles don't go away, merely sticking
them with a needle and more rubbing will do the trick. The tape was
overlapped about 1/4 inch from one strip to the next so the epoxy can't get
to the balsa.

Of course, the inside of your part will not be super smooth but in most
cases, that's not a problem.

Dan Schaefer