epoxy over fiberglass

[sand some more]

I have a cold molded sailboat that someone glassed below the water line I have removed just about all of it but there is still a thin layer in low spots. can I leave that there and start to fair it up using an epoxy fairing compound
thanks
lee

[Keith Wilson]

Yes.

[Buddy]

Yes, but- how did you remove it- chip away, peel away with chisels and scrapers, or truly abrade away with sandpaper as your post suggests? Was the fiberglass applied with epoxy or polyester resin? Epoxy would have been hard to remove by peeling, if it came off relatively easily in pieces, and it it smelled like model airplane glue when you were sanding, it was polyester. If polyester was involved, this stuff does absorb moisture readily. Some moisture will get past the new epoxy on a boat left "permanently" in the water and you'll likely get blisters as the poyester resin swells up. Trailered boat, don't worry. Cold molded boat likely used epoxy resin all the way, but COLUD be done with resorcinal or airolite glue building the hull, and then polyester on the glass sheathing.
If polyester, how much work to get it all right now?

In any case, I would roll on a coat of unthickened epoxy resin and let it tacky, then put on your first epoxy/ filler fairing material si it can cure together for best adhesion. After you've filled and faired all you can stand, I would again roll on a coat of unthickened epoxy to seal all the open spheres of the filler you've been using bbbbbefore you start with your paint system. I still like to use a two part epoxy primer under my topcoat even though you'll hear loots of folks don't. IMHO its just more reliable, more easily smoothed. On a modern coating system- the primer does the real leveling and coating work. The LPU topcoats all together are precious thin, maybe only 25% of the coating systems total thickness. You'll have to do more work on the harder epoxy sealer coat to get the same final surface quality using just a one or two part topcoat.

[sand some more]

I started using a heat gun a scrapper but it was going real slow and in spots pulling up some wood with it. I switched to sander it went alot faster but was real dusty. I have a big clean up project before I do anything elase. It did smell like airplane glue. I do plan on leaving it in the water for weeks at a time.
Lee

[Buddy]

I feel pretty sure you have polyester resin there. Now epoxy will stick just fine to polyester. Regular fiberglass hulls are repaired more strongly with epoxy and glass all the time so no worries about that. Are you going to reglass that bottom or just rely on reguklar antifouling bottom paint if you don't need abrasion or marine borer protection to the greatest degree? If you are not reglassing, then there's not much point in getting the rest of the polyester off. If you are going to glass the bottom or the whole hull, I'd make a one more effort and clearing off anything that could be polyester filler ( like Bondo) below the waterline. Just hard, clear or colored polyester resin could ride.