1. To make a seamless repair over a deep fiberglass scratch or crack, it's important to widen and smooth the fissure prior to application of epoxy resin patching compound.
2. Select a tungsten carbide cutter that is appropriate for the crack you're working with. Holding the tool at a 45 degree angle, create a V-shaped groove along the length of the scratch.
3. Press resin into groove with plastic applicator. Let cure overnight, then sand with #240 wet/dry sandpaper. Finish with soaked #400 sandpaper and apply gelcoat enamel to finish.
Courtesy of Dremel Tools