Currently working on a fiberglass bodied dune buggy. Other than the original gel coat, the body has been painted once around 2016. That paint consisted of a layer of primer (definitely not a high build) and a base color + Clear coat. I've started the bodywork, correcting the previous repairs that used a regular body filler rather than actually repairing fiberglass and using a body filler made for fiberglass. The areas that need repair get taken down all the way to bare fiberglass. My question is how far down to I need to sand the other areas. I know that there's no way to see all of the potential problems without removing the latest respray, but can I stop at the original gel coat layer or do I need to strip EVERYTHING down to the bare fiberglass? My original thought was that I'd take it down to the gel coat, cover with an epoxy primer and follow that a high build primer to block it? While I don't want to waste time sanding if it isn't needed, it would be way worse to waste the sanding time, the materials cost, AND additional time to re sand because of a skipped step that causes an issue. Any guidance greatly appreciated.

Youtube taught me to use epoxy on metal and over filler. But... If your sealer is an epoxy, this step can be skipped? So instead of epoxy on filler ud be applying reduced epoxy over 2k, before base. My guess: yes it would work. Why wouldnt it. Another headscratcher.. spi epoxy tds says 320grit over paint at most. But sealer requires 400 so how would that work even? My guess: idk, analysis paralysis. 320 what if it shows, 400 what if it doesnt adhere.. need Aaron on this one I got a quart kit of epoxy, planned to use a bit for bare metal and seal everything before base but now im thinking i might run out, and my 2k urethane states you can base over it without sealer. So maybe thats the way...cuz i have a gallon kit of the 2k.. My guess: its spi so if they say you can apply color over their 2k urethane they are not lying. It would just come down to color. Black epoxy sealer would work only for very dark colors: dark cherry red, dark blue, midnight purple, but grey would work for pretty much anything except for white yellow and like that I grabbed the black epoxy and if used as a sealer it limits the colors you can do but the urethane is grey so the choices would open up.. tbh. I dont care what color it will be.