: If there are pits, blisters, gouges, scratches or other defects or blemishes
: you will want to repair them before painting. Epoxy resin will work fine.
: You can add filler materials (like flour, finely ground plastic powder, or
: glass micro balloons) to thicken it into a paste for filling depressed
: areas. Let it harden and then sand it smooth. Scraps of glass cloth can be
: used for reinforcing any areas that need more extensive repairs.

Microballoons make a terrific low-weight fairing compound. After sanding though they leave a rough surface; each sanded MB becomes a pinhole. The fix is easy though, a seal coat of epoxy over the patched area, followed by more sanding.