by GreenLake » Wed Jul 26, 2017 9:15 pm
There are gel-coat cracks and then there are cracks in the laminate. If you can push one side, it seems you have a crack all the way through the laminate.
My approach would be to grind the area around the crack to a 1:12 bevel and then fill back in with fiberglass cloth (!) and epoxy. Epoxy gives you a stronger bond which is something to think about when you suspect that the original laminate wasn't strong enough.
Because you can't really get at the area from below, your only chance at reinforcing it is by adding a layer on the top. That will be visible as a raised area, but you could try to otherwise make it look like a neat patch (square edges, sanded smooth, etc.) Thing is, with epoxy, you need to cover it against UV.
Normally, people say paint it, but if you use a no-blush epoxy (like System Three Silvertip) and mix it in very accurate proportions then coating it with gelcoat like for the repair shown in the video, should be possible. You could also get a more specialized product, such as SB112 from SystemThree which is actually formulated for use with gelcoat (intended for building surf boards).
You could of course use polyester resin as shown; it may be strong enough, after all. (Can't really tell where in your boat that crack is located). Worst will happen it cracks again.
If you grind a bit too far, I wouldn't sweat a gap if it's 1/2" or less If you fill your crack by putting the largest patch down first and then succeedingly smaller patches the first patch of cloth will be well anchored on the sides of your repair. It will dip through a bit, but I assume you don't care that the underside is smooth. If you worked by putting the narrowest one down first, that could push through.
~ green ~ lake ~ ~