Fiberglass PROS help please. Stress cracks.

[enkeivette]

So on the top surface of my boat there are what look like hairline, spider veins type cracks in the fiberglass. I'm worried that if I simply paint over them they will show through.

So what's the best way to remedy this? Hit the surface with a grinder and fill it?

Or can I just sand the surface with 40 or 80 grit, lay down one piece of matte and resin right over the old fiberglass, sand, fill and sand till it becomes part of the boat?

 

[enkeivette]

The boat is a 69 so I'm guessing the fiberglass is polyester.

 

[saudivette]

I'd grind the cracks out. I found some hairline cracks in my front panels and ground them out with my Dremel and a small ball end bit. I filled them with 3M8115 and rubbed it back.

If you ground them out then put your mat and resin over the top of that, I don't think they'd ever come back.

 

[enkeivette]

I can't trace them like I did with the Vette bumper, there are too many. If I grinded them I would need to do it with an actual grinder over a large area.

But if I'm laying matte, is there any reason to grind anything? Might as well keep it flat to make less work for myself right?

 

[010752]

Gelcoat cracks are a completely different animal than cracks in a Corvette ( has no gelcoat)
Usually on the top of a boat, the deck areas are too flexible for the gelcoat which is fairly brittle.
Probably best is to sand most off to the glass and paint with a good marine paint. Use a good da with 60 or so discs. Grinders are too agressive. Lots of work. If keeping the boat, best to reinforce underneath.

Google for different repair methods.

 

[mrvette]

I dunno, be ME, I"d spend more time running the sox off that thing .....

:beer::beer:

 

[saudivette]

Gelcoat cracks are a completely different animal than cracks in a Corvette ( has no gelcoat)
Usually on the top of a boat, the deck areas are too flexible for the gelcoat which is fairly brittle.
Probably best is to sand most off to the glass and paint with a good marine paint. Use a good da with 60 or so discs. Grinders are too agressive. Lots of work. If keeping the boat, best to reinforce underneath.

Google for different repair methods.

I should have said, but my front fender and nose cone are reproduction pieces and are gel coated :lol:

 

[mrvette]

Gelcoat cracks are a completely different animal than cracks in a Corvette ( has no gelcoat)
Usually on the top of a boat, the deck areas are too flexible for the gelcoat which is fairly brittle.
Probably best is to sand most off to the glass and paint with a good marine paint. Use a good da with 60 or so discs. Grinders are too agressive. Lots of work. If keeping the boat, best to reinforce underneath.

Google for different repair methods.

I should have said, but my front fender and nose cone are reproduction pieces and are gel coated :lol:

I heard your WIFE said that.....


OUCH!!!!!:tomato::tomato::lol:

 

[vette]

So on the top surface of my boat there are what look like hairline, spider veins type cracks in the fiberglass. I'm worried that if I simply paint over them they will show through.

So what's the best way to remedy this? Hit the surface with a grinder and fill it?

Or can I just sand the surface with 40 or 80 grit, lay down one piece of matte and resin right over the old fiberglass, sand, fill and sand till it becomes part of the boat?

If the boat is lacquer then this is going to happen. Hence lacquer paint. 1969 it could be. Do not grind the cracks, no need too unless they are in the fiberglass. Strip it down to glass (chemical or sandpaper) and repaint it with modern day paint and you will be fine.

Danny

 

[MYBAD79]

I'm afraid that if you hit it with 80 grit you won't be able to tell if the cracks are really in the fiberglass.... strip with a razor blade or chemical stripper and if the cracks are in the glass THEN hit it with a grinder, 40 grit, mat and resin. I would not simply use filler without mat but that's just me.... the cheap and simple "grind and fill" repair might last a few years....

 

[enkeivette]

I'll try to get out there and check it out, but it looked like the cracks were in the glass. But so many people seem to think they're in the gelcoat, hopefully it's just gray gelcoat and I couldn't tell the difference. I'll keep sanding.

Karsten, if you wipe the glass down with laquer thinner they'll stay highlighted for a few seconds while it evaporates. It's how I found the tiny tiny spider veins on my bumper that didn't stand out like the big ones.

 

[enkeivette]

I'm afraid that if you hit it with 80 grit you won't be able to tell if the cracks are really in the fiberglass.... strip with a razor blade or chemical stripper and if the cracks are in the glass THEN hit it with a grinder, 40 grit, mat and resin. I would not simply use filler without mat but that's just me.... the cheap and simple "grind and fill" repair might last a few years....

Took the rear bumper (aftermarket fiberglass) down to bare glass on the Vette with 80 on a DA. Trust me, laquer thinner highlights the cracks. It's a very useful trick. As it evaporates it stays in the cracks a bit longer than everywhere else.

Btw, I've pretty much stripped the boat already with a 80 on a DA.

 

[010752]

It's a common problem down here in S Florida (boat capital of the worlds supposedly) and big business to repair stress, and paint boats.

Interlux and Awlgrip are used a lot. Nasty job to sand off gelcoat and prep for an epoxy paint system, but that's how they all do it. The piant will repair and seal if they really are just stress cracks. Paint is a lot more flexible than the original polyester gelcoat.