: I'm wondering if I can just sand whatever resin it is down and bond to it
: with epoxy? I've gotten conflicting answers from credible experts, which
: is why I'm asking more here. Someone suggested that if it's vinylester
: resin, the epoxy won't bond.

I don't know about vinylester but I built a sailboat many years ago and covered it with glass & polyester. The wisdom at that time was polyester wouldn't stick to epoxy but epoxy would stick to polyester. I did some epoxy on work top of the polyester at the time and had that boat over 10 years without the epoxy separating.

John