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Guys,

I recently pulled the rod holders out of the covering boards to start prepping for paint. It is balsa cored (B35) and I want to seal up the penetrations so it can never get wet...even if caulk leaks. I've ground/chiseled out the balsa between the two fiberglass skins a little past the screw holes but left the skins intact. Can I just fill with thickened epoxy or will the epoxy be too brittle for the stress from the rod holders?

Thanks,
Mark

Mark,

Virtually any grainy substance will be water proof when thoroughly mixed with epoxy, even saw dust... One of my favorite materials is vermiculite, available from garden centers & sold as a soil amendment. Thicken your epoxy first with Cabosil to the consistency of mayonnaise and then add your filler to bring it to the consistency of peanut butter and pack away.

Thickened epoxy would be ideal.
Make sure you prep the area to receive the epoxy thoroughly, clean everything with denatured alcohol, and it wouldn't hurt to do an initial "primer" application of straight epoxy, or even reduced epoxy so that it creeps into the substrate well.
To thicken, I'd use silica...

Perfect, thanks guys