RE: Hysol and Polyester Fiberglass Resin Compatibility
The general rule is: Epoxy over Polyester is ok, vice versa is not. I have used epoxy on polyester resin successfully many times. Polyester won't cure over epoxy.
Polyester resin will cure just fine over 5 min epoxy, however, polyester will cure over 30 min epoxy, but very slowly. Like 24 hours at least. Whenever I use 30 min epoxy to join foam cores, I have to seal the seam with 5 min epoxy before applying fiber glass cloth and polyester resin.
Before I use any adhesive on the inside of a epoxy glass or fiber glass fuselage, I wipe with acetone and then scuff the surface. If it's an epoxy glass fuselage I use 5 min epoxy. If it's a polyester resin fuselage, I use polyester resin. I've never had a problem with polyester bonding to polyester. But since most all fiber glass parts today or epoxy resins, just use 5 min epoxy.