I didn't really do much grinding on the dings and gouges, I just filled 'em, but I suppose some grinding wouldn't hurt. Most of what I had to deal with involved low spots in the gel coat that was fairly porous, so I wasn't too concerned with adhesion. Being epoxy, the Fasco stuff should have good bond strength. It seems to have about the same strength as Marine Tex when cured so it's pretty tough stuff, but it has a thick creamy texture when first mixed, so it spreads real nice. It's been 4 years since I did the bottom; I've run the boat well over 1000 miles since then, some of it in pretty rough stuff, and I've had zero problems with cracks or disbonding of the filler.
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