5. When sanding fiberglass parts, work slowly and carefully to guard against sanding through the "gel-coat." If you sand through the gel-coat, you've gotten into the actual fiberglass material used to construct the hood. If you do go through the gel-coat, you will need to fix the mistake spot with fiberglass resin and/or primers. The photo shows what it looks like when you've sanded through the gel-coat (notice hood edge).