: Howdy! I'm doing some modifications to a glass boat. It is old and seriously
: worn. No idea how old, what it is made of, ect, but it looks to have sat
: in the sun for about ten years.

: 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.

Epoxy is pretty much the universal adhesive for fiberglass repairs. Use it for any gluing or repairs you are doing.

Don't use it as a general coating over the entire boat. Paint or clear urethane 'varnish' work better for that.

After your modifications are complete, wash the boat well, give it a light sanding ( you can do this by hand with a sanding block) with 150 grit sand paper, and paint it. That gives a durable finish and protects the epoxy, or any other resin, from further UV damage.

: Here is a photo of the inside of the boat, is that kevlar? how can I tell?

The only way to really tell is to sand into it and get a sample. That does more damage than you might want to do. Let's just assume that it is.

When you paint the boat you can have it any color you want. If you like the look of the woven fabric, use a clear coating.