I have a Kevlar surf kayak with a few minor cracks/cave-ins from rocks. I want to patch the boat up and refinish with gel-coat (bottom) and Urethane (top). I'm concerned about adhesion though. I've seen fiberglass patches delaminate from gel-coat. Do I need to sand down to the fiber/epoxy or can I go over the gel? I'm planning on using West Marine epoxy with e-glass (I forget the weight).