Sealing Balsa Core

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#1

End grain balsa can act like a sponge, sucking up heavy resin
with a great thirst unless sealed. The question is how best to
seal it. I have come up with a couple of variations on the
theme.

First, thicken the resin (epoxy) with colloidal silica to the
mayonnaise, or maybe creamy peanut butter consistency and spread it with plastic (Bondo-type) blade. An eyeball guided process
to get as thin and even a coating as possible. To get a good
bond, the subsequent plies would have to laid on before the seal
coat is fully cured. For a one man operation this could present
some problems.

The second approach would lay on a layer of thin (3/32 or 1/8)
aircraft grade plywood while the sealer is chemically bondable.
Plywood would have to be clamped or vacuum bagged to minimize
voids. Subsequent plies could be applied at a later time as
the getting a bond with the wood should be straight forward.

If a guy got an early start and had all the materials staged,
doing both sides of a large panel in one day should be
possible with the second approach. Large = 4’ X 7’

If anyone has some alternate suggestions, please come forward.

Thanks for your help.

#2

we have made some pretty big Carbon/balsa panels, they were 60’ long, 4’ wide. never sealed them though. we used a epoxy that had a higher viscosity, didnt notice too much resin absorbtion, but of course weight wasnt a big concern for these panels. made the panels in about two hours with 4 people, vacuum bagged them. if your concerened about time, use a slower hardener. This will also help pull out excess resin because it will flow better at time of vacuum.

#3

We have just brushed on a coat or 2 (depending on resin) of the resin used in the infusion to seal the core. i think that is the best way to do it.

#4

You can use Benite on the core. It needs a day or so to fully dry.

You can find it in the paint dept at Home Depot or Lowe’s. It will seal the surface of the wood and stop it from wicking. its thin enough going on that it wont change the size or leave marks. I would not use it with prepreg but it should not be affected by resins.