Fixing spider cracks before paint.

I spoke to an automotive service manager the other day about prep techniques for a glass car. I explained that I had a couple of spider cracks in the gel coat ( over the rear lights ) and asked about their treatement prior to paint. No sweat he said...plenty of experience with old Vettes. They apply heat and more or less rub things back together. I've never even painted a glass boat. Any comments on the idea ? Thanks.

I use a die grider and cut grooves down into where each spider crack is..IMHO it's the only and right way to stop their return.

Yup, that's the way I understand it too, Alan. Do you recommend any specific filler after grinding out those cracks ? Generic Bondo or something made exclusively for fibreglass ?

DO NOT use bondo - unless you want to do it over and over. West Marine has an epoxy filler system - basic kit is about $40.

I am working on the glass right now and using the techniques learned above. I bought the West System stuff but it is a ton of money. I also bought the AeroMarine Epoxy and it works just as good and is way cheaper like 95 bucks for a gallon and a half. I am going to not only grind out the spider cracks and fill but also lay some glass on the back side. I also have spider cracks above my rear lights so that must be a high stress point.

David,

Depending on what year Corvette the guy had in mind, the bumpers weren't fiberglass/gelcoat, they were urethane. All the way back to the 70's.

Urethane bumpers can be heated and "welded" back together. Minor surface cracks, just heat and rub, big cracks, even breaks can be "welded."

I've never seen gelcoat repaired like that. The fiberglass underneath has give, gelcoat tends to be a little more brittle. We usually sand the gelcoat off and reseal. If anything at all is in the 'glass, that gets ground, chased to the ends, and filled with glass.

(then again, Steve seems to hate gelcoat - so take above with a grain of salt!)

angela