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Bertram31.com General Bulletin Board
Re: Best Way to Repair Holes in Fiberglass?
Posted By: Capt Patrick McCrary In Response To: Best Way to Repair Holes in Fiberglass? (Vince L.)
Date: Tuesday, 31 May 2005, at 10:27 p.m.
Vince,
Small screw holes, under 3/8" don't usually require the addition of fiberglass if patched right...
First, counter sink the hole, opening the diameter to about twice the hole diameter. With a piece of 80 grit sandpaper, blur out the counter sink so that the edges are feathered into the finish surface of the surrounding surface.
Clean the hole with denatured alcohol and wipe in a thin layer of un-thickened epoxy. The exposed raw fiberglass should be completely wetted out with the epoxy, but wipe away all excess epoxy, leaving the hole virtually dry. This primes the surface for better bonding with the filled epoxy. Allow the epoxy to cure until it is barely tacky, but not hard.
Epoxy has a large shrinkage rate during the first 48 hours of the cure. With epoxy thickened with Cabosil, (fumated silica), and high density filler, (milled fiberglass), fill the hole, but leave the epoxy dimpled slightly below the finished surface. Allow this stage of the patch to cure for a minimum of 48 hours. A week would be better if you have the time...
Re-sand the patch, clean again with denature alcohol, and re-prime as described before. This time thicken your epoxy with a small amount of Cabosil and then add microballoons to thicken on to the consistency of thick peanut butter.
Over fill the balance of the hole, leaving no bubbles & about 1/16" above the finished surface. Again, allow to cure for a minimum of 48 hours.
Using a sanding block and 220 grit paper, sand the patch flush with the finished surface. You're ready for paint...
If you are going to re-gelcoat, re-sand the patch to be about 1/32" below finished surface with 80 grit paper, clean, and apply your gelcoat to be above the finished surface. Allow to cure for 48 hours & block sand with 360 grit to surface level. Be sure to add a small amount of surfacing wax to the gelcoat before adding the MEKP. This will give you a sandable surface.
Continue your sanding with wet paper, 400, 600, 1,000, 1,500 grits. Finish with light compounding and polish.
Best regards,
Patrick
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