Sunburnt Fiberglass
- Thread starter penno
- Start date
Jim Rosenthal
Supporter
This is more a cosmetic issue than structural, isn't it? probably your best bet is to clean it up, sand it, and recoat with a good epoxy high-build primer to seal the gelcoat, then sand that, reprime it, and do your finish coats.
Jim is correct in that if the cracks are just cosmetic in the gel coat: Sand, fill and prime.
Look at the "interlux" brand paint booklet that tells you how to treat old fiberglass. Re finished a 2t ft 1967 Pearson Renegade sailboat 3 years ago. One of the first fiberglass boat. The rumor was that since they didnt know much about fiberglass at the time, so they laid it up very thick. This boat was known for deep stress cracks in the gelcoat. Did in the above order (sand/fill/sand/primer/sand/final coat). ROLLERED 2 coats of one part urathane (sp?) and tipped out with a brush: could see your reflection in it! I'm an amature and spraying was out of the question: to dangerous and too much skill needed. I did the whole boat myself I can't post pictures, bt If anyone can, I will email them the picture to post. Also did a 16 ft 1964 aluminim boat. Now have an 1980 36 to do. LOTS of info available from the marine suppliers. cb
Look at the "interlux" brand paint booklet that tells you how to treat old fiberglass. Re finished a 2t ft 1967 Pearson Renegade sailboat 3 years ago. One of the first fiberglass boat. The rumor was that since they didnt know much about fiberglass at the time, so they laid it up very thick. This boat was known for deep stress cracks in the gelcoat. Did in the above order (sand/fill/sand/primer/sand/final coat). ROLLERED 2 coats of one part urathane (sp?) and tipped out with a brush: could see your reflection in it! I'm an amature and spraying was out of the question: to dangerous and too much skill needed. I did the whole boat myself I can't post pictures, bt If anyone can, I will email them the picture to post. Also did a 16 ft 1964 aluminim boat. Now have an 1980 36 to do. LOTS of info available from the marine suppliers. cb
If the cracks are only in the gelcoat, you'll still have to remove the flaws completely by sanding or grinding. I would try to remove ALL the car's most vunerable gelcoat - it's likely that cracks will propagate in new areas eventually. Once the car is "clean", spray with an epoxy-based filler and block out to shape.
Wear a dust mask...
Wear a dust mask...
Bob-Is that REALLY necessary to sand out the cracks? There are techniques of filling the cracks with good filler (3m) and snding them down. The cracks have to be cleaned and scraped to a V (dental tools if very small cracks). My bible (for boats) is the latest addition of "This old boat" Really. Always willing to lean. Not about to quit my day job. cb
Bob is right on the money. I've done some Lotuses that were so bad, I had to put a layer of fine weave fabric over the whole top-side of the car...after using a 'DA' sander to remove all the gelcoat down to the glass. Most of the fine glazing putties are not fine enough to fill the hire-line cracks, so they will just show up again with time.
Peter Delaney
GT40s Supporter
Unfortunately, I think that the hard way is going to be the right way. If there are only a few cracks,you could just sand back broad areas around the cracked gelcoat, right back to the glass & lay on a high-fill 2-pack poly filler, stacking it on the sanded areas so that you can block the whole surface back to perfection. If the cracks are everywhere, you can bet there are heaps more under the surface, waiting to show up just after you finish the final paint job !
If this is the case, it would probably be best to strip all the gelcoat off (air powered rotary & orbital sanders will do this fairly quickly) & then lay about 3mm of the filler over the whole car.
I have a '71 Vette under resto by a professional & he has tried all sorts of approaches over the years. He has finally settled on the Spies Hecker (DuPont company) system & is getting fantastic results.
Everything is 2-pack, starting with Raderal 3508 high-build polyester filler, then Vario Primer/Surfacer 8590, then Permacron 293/295 Base Coat & finally Vario Clear Coat 8000 or Permacron Clear Coat 8110.
After watching the "expert" do the 'Vettes, I have started to do the '40 myself - I have a couple of panels in Raderal & have blocked them back to 320 grade so far - easy to do & a great finish. All you need is a "putty gun" with a 2.5mm nozzle & away you go - you can't really put too much on & you don't need to worry about runs - it all blocks back beautifully, ready for the primer.
At that point, I'll let the "expert" do the base & clear coats (tried that once & really stuffed it up !).
What a lot of waffle !! I guess that the long & short of it is that you could do quick "dig-out & fill" job on the cracks, then prime & top coat, but the risk is that other cracks may show up before long. To nail the problem permanently, it would probably really be best to strip the gelcoat off & do the job properly.
Kind Regards,
Peter D.
If this is the case, it would probably be best to strip all the gelcoat off (air powered rotary & orbital sanders will do this fairly quickly) & then lay about 3mm of the filler over the whole car.
I have a '71 Vette under resto by a professional & he has tried all sorts of approaches over the years. He has finally settled on the Spies Hecker (DuPont company) system & is getting fantastic results.
Everything is 2-pack, starting with Raderal 3508 high-build polyester filler, then Vario Primer/Surfacer 8590, then Permacron 293/295 Base Coat & finally Vario Clear Coat 8000 or Permacron Clear Coat 8110.
After watching the "expert" do the 'Vettes, I have started to do the '40 myself - I have a couple of panels in Raderal & have blocked them back to 320 grade so far - easy to do & a great finish. All you need is a "putty gun" with a 2.5mm nozzle & away you go - you can't really put too much on & you don't need to worry about runs - it all blocks back beautifully, ready for the primer.
At that point, I'll let the "expert" do the base & clear coats (tried that once & really stuffed it up !).
What a lot of waffle !! I guess that the long & short of it is that you could do quick "dig-out & fill" job on the cracks, then prime & top coat, but the risk is that other cracks may show up before long. To nail the problem permanently, it would probably really be best to strip the gelcoat off & do the job properly.
Kind Regards,
Peter D.
G
Guest
Guest
I might throw one word of caution here. You didn't say if this is just the body or a complete car. If it is a complete car and the various joint lines all fit nice and there is no sagging or distortion in the panels, then go for it.
If it is just a body, be careful. One of the other bad things that happens to fiberglass that has been exposed to sun/heat for a long time is that it creeps. The material will sag and stretch. You may find that, after you've done endless hours of cosmetic repair, the panels and clips just will not line up. (As you might guess, seldom is the sagging and creeping done in unison for the different sections.) So spend a good deal of time closely studying how the major sections come together and look in general. Large open areas (usually fairly thin) will fare the worst; areas with curves, especially where different radii come together and where subsections are bonded together will fare better. Sometimes these are the worst though because, while they look good to the eye, when you finish your car, a 1/4" misalignment can look really bad when it some where like where the rear clip mates to the spyder.
If it is just a body, be careful. One of the other bad things that happens to fiberglass that has been exposed to sun/heat for a long time is that it creeps. The material will sag and stretch. You may find that, after you've done endless hours of cosmetic repair, the panels and clips just will not line up. (As you might guess, seldom is the sagging and creeping done in unison for the different sections.) So spend a good deal of time closely studying how the major sections come together and look in general. Large open areas (usually fairly thin) will fare the worst; areas with curves, especially where different radii come together and where subsections are bonded together will fare better. Sometimes these are the worst though because, while they look good to the eye, when you finish your car, a 1/4" misalignment can look really bad when it some where like where the rear clip mates to the spyder.
