During curing the surface epoxy developed two problems: Irregular surface dent from large bubbles between the epoxy and wax-paper protection layers, and micro-bubble pinholes from the plywood and fiberglass cloth degassing. Here they are highlighted because they are full of fiberglass dust after a light sanding.
I’d encountered degassing resin problems before while building my Arc Reactor prop and new that there was only so much you could cure with higher temperature epoxies and curing. Since this surface was to be painted I would deal with it post-cure.
I experimented with Cabosil-Aerosil thixatives and epoxy but found that an epoxy-based filler was far too hard to be able to sand down without damaging the existing epoxy finish down to the fiberglass cloth. I guess this is why we test on scraps.
I’d planned on using Elmer’s Carpenter Wood Filler as a patch for the body tubes and thought I’d give it a try here.
Worked great! Takes two or three passes of filling with a popsicle stick and sanding with very fine sandpaper. A mix of 3 parts Filler with 1 part water softens the filler enough to “flow” into the finer bubbles….but they do have to be filled individually. Too much filler on the larger surface means more sanding and that means risking sanding down to the fiberglass cloth and ruining the fin.