Re: 1978 Ericson 27 fiberglass repair, which resin??
I hope I don't add to the confusion.
West Systems is a fantastic product when used correctly, so make sure you use it correctly.
First bevel the edges of the hole from the outside as much as possible to increase the surface area of the hole. I like to use a rasp (a wood bastard file). Clean the interior surrounding fiberglass, sand it to remove any paint and rough up and expose clean fiberglass.
Paint the inside with unthickened epoxy, and when it begins to kick, lay on a bandage of biaxial cloth that overlaps the hole, and paint the fiberglass cloth with enough epoxy to saturate it.
Wait for the epoxy on the inside patch to begin to cure, still tacky to your finger, and lay on a biaxial round patch the size of the hole on the outside and paint with epoxy. Cut circular patches each ¼” or so larger than the last to build up layers of fiberglass that overlap onto the beveled outside edge you created earlier. Add layers to bring the thickness close to that of your hull—however thick that is—and finish, again when the epoxy is still tacky, by thickening some epoxy and fairing the patch.
When it is completely cured, wash the area with clear water and a 3-M scrubee to remove the anime blush from the epoxy. Sand the exterior with 80 grit sandpaper to knock off the high spots and make the low spots, if any more visible. Use more thickened epoxy to fill the low spots until you have a smooth finish.
Fiberglassing is chemistry. Mix the parts per spec. Too much activator and the mix will get superhot and pot life will suffer. Mix a small batch exactly per instructions and practice on something - get used to pot life and how much time you have to work it. A larger batch in a deep tub will activate faster as well - its got to do with the chemical reaction.
Compliments of another forum. It's too late to type all that out.
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