I have a 1972ish sunfish I am planning to re-gelcoat the entire bottom of the hull. I made one fiber glass repair where there was a crack through the hull, I took that area down to bare fiberglass before repairing. In another area cracks in the gecoat turned out to be related to a thick layer (3/4 of an inch, 2 cm) of bondo over an old repair. I sanded that area to the fiberglass, unsure if I am going to add more fiberglass, but not replacing the bondo that thickly.
Where there are scratches or spider crackes I sanded until they were gone, mostly there is still a layer of gelcoat, in few place there is a little fiberglass showing. For the most part 95% of the hull has a layer of gelcoat sanded with 60 grit.
I have purchased two quarts of white exposy gelcoat, one laminating and one waxed for the final coat.
Some research I have done suggest the thick gelcoat is part of the reason for spider cracks (when the fiberglass flexes the gelcoat cracks).
My plan at the moment is, a coat of laminating gelcoat on bare fiberglass, a second coat of laminating on the entire hull, a third coat of waxed/final gelcoat on the entire hull, sand with 400-600 grit and put the trim back on. All gelcoat will be applied with a brush.
Should I sand the entire hull until the gelcoat is mostly gone? If I consider existing gelcoat as one layer, what the is the maximum number of coats that should be applied over any area of the hull?