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Old 24-05-2020, 11:50   #1
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Re-Gelcoating - How to deal with this crazing?

I'm planning to re gelcoat the sides of my coach roof at some point in the near future.


There's a fair bit of info on the process out there & I'm going to give spraying a go, however I've got loads of crazing and cracks in the old gelcoat.



(see below pic)

What's the best way to deal with this? It doesn't really seem feasibly to take the dremel and grind out every crack & fill it, I'd still be here in ten years.

Should I just buy some 40 grit discs & blitz it back to with the sander until they're gone, or is there a better way?
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Old 24-05-2020, 13:05   #2
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Re: Re-Gelcoating - How to deal with this crazing?

I would mix up an epoxy fairing compound and skim coat it, sand and prep for gel (remove amine, sand and clean)
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Old 24-05-2020, 18:29   #3
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Re: Re-Gelcoating - How to deal with this crazing?

Remove the dodger, or whatever that fitting is, and figure out a backing plate for those attachments, first. It has been wonkling under load, when people lean on it or pull on it getting in and out of the cockpit.

Then do the cosmetic work.

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Old 24-05-2020, 19:10   #4
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Re: Re-Gelcoating - How to deal with this crazing?

I wouldn’t say they were stress cracks but it will be easier to fix with the fitting removed.
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Old 24-05-2020, 21:17   #5
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Re: Re-Gelcoating - How to deal with this crazing?

The fitting has already been removed, someone had only installed it with self tappers.

However the gelcoat has lots of this crazing in plenty of locations that don't have fittings attached.
And if you observe the cracks they aren't really radiating from the fitting, mayber there is excessive flexing in that part of the coachrooof?

As to fixing them, will an epoxy mix get the penetration I need? The cracks are rather small. I guess maybe its better to make a very running fairing mix and to try and give it the best chance of penetrating the crazing?
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Old 24-05-2020, 23:19   #6
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Re: Re-Gelcoating - How to deal with this crazing?

Mix it thick enough so it doesn’t drip. Skim over it, wash it, sand and finish. Put just enough on to cover the crazing but not too much as it can be a pain to sand down. you could also try marinetex or similar (easier to sand) but epoxy would last.
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Old 25-05-2020, 08:37   #7
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Re: Re-Gelcoating - How to deal with this crazing?

Just finished this job on Nanamuk's feature stripe. I started with 2 coats of S1 sealer using a 2" spatula to work it into the cracks 5 to 10 minutes after applying, it is 50% solids so loses volume as the solvent evaporates. This also prevents too much build up which is hard to sand off. I then top skimmed with Cold Cure epoxy thickened a bit with West 207, again with the 2" spatula and as thin as possible - if you thicken it too much it will pull back out of any voids - too little and it sags and is harder to sand. Painted with Brightside and none of the cracks are visible - time will tell if it is a long term fix.
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Old 25-05-2020, 13:57   #8
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Re: Re-Gelcoating - How to deal with this crazing?

Thus type of crazing is caused by too thick original gelcoat. Resins and gelcoat shrink, the gelcoat more so than the resin/Fiberglas underneath. Solution is to grind gelcoat down to near the glass base and then prime and paint with a top coat paint not gelcoat. Alternately, overlay thin layer of Fiberglas and resin and sand down to repaint.

Fillers will only buy you a bit of time before cracks reappear.
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Old 26-05-2020, 07:05   #9
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Re: Re-Gelcoating - How to deal with this crazing?

I agree that the crazing is not a problem. I re-gelcoated my deck and there were a few places that looked like that. I sanded them down well and shot gelcoat over them and so far has not been a problem. I am confident that there won't be a problem.
Don't however, use epoxy filler if you can avoid it. The amine will come out over time and release the gelcoat. If you do use epoxy filler coat it with 545 primer. This is not the best plan because the primer is soft compared to the gel.
I used one of these and I loved it. I made spraying gel much easier.


Additionally, I used Duratec additive to thin and make the gel flow better.
https://www.fibreglast.com/


Read Minert's post:
https://www.cruisersforum.com/forums...fit-95666.html
cheers!
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Old 26-05-2020, 08:06   #10
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Re: Re-Gelcoating - How to deal with this crazing?

Quote:
Originally Posted by jhulmer View Post
I agree that the crazing is not a problem. I re-gelcoated my deck and there were a few places that looked like that. I sanded them down well and shot gelcoat over them and so far has not been a problem. I am confident that there won't be a problem.
Don't however, use epoxy filler if you can avoid it. The amine will come out over time and release the gelcoat. If you do use epoxy filler coat it with 545 primer. This is not the best plan because the primer is soft compared to the gel.
I used one of these and I loved it. I made spraying gel much easier.


Additionally, I used Duratec additive to thin and make the gel flow better.
https://www.fibreglast.com/


Read Minert's post:
https://www.cruisersforum.com/forums...fit-95666.html
cheers!
Those look pretty slick. As for the amine, soap and water wash before sanding will take care of it.
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Old 26-05-2020, 08:36   #11
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Re: Re-Gelcoating - How to deal with this crazing?

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Those look pretty slick. As for the amine, soap and water wash before sanding will take care of it.
It does remove it from the surface and is fine if painting. But, if putting Poly gel over epoxy it works for a while then the amine slowly works to the surface of the epoxy and will release the gel. This is the experience of the experts. Reading Minaret's post he points this out and he is a professional with the experience of it lifting.
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Old 26-05-2020, 08:43   #12
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Re: Re-Gelcoating - How to deal with this crazing?

I was just re-reading parts of Don Casey's Sailboat Hull & Deck Repair yesterday, and he mentions crazing or alligatoring. As already mentioned, he puts it down to either localized stress, or too-thick gelcoat.

The book offers two suggestions (quick summaries; see the book for full details):
  1. If the crazing is just in specific areas, grind some of the thickness of crazed gelcoat off, and put down a good coat of new gelcoat.
  2. If the crazing is pretty much all over, paint it : good surface prep, two coats of a high-build epoxy primer, sanding between coats, then a two-part polyurethane paint,

It's recommended to do the smooth and nonskid areas separately.

Also, I read somewhere that white vinegar is very good for removing amine blush, so that's what I've been doing when epoxying.
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Old 26-05-2020, 08:55   #13
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Re: Re-Gelcoating - How to deal with this crazing?

Quote:
Originally Posted by jhulmer View Post
It does remove [blush] from the surface and is fine if painting. But, if putting Poly gel over epoxy it works for a while then the amine slowly works to the surface of the epoxy and will release the gel. This is the experience of the experts. Reading Minaret's post he points this out and he is a professional with the experience of it lifting.
There's a PDF from Gougeon Bros (WEST Systems) out there about some extensive tests of gelcoat over epoxy, which concluded that the bond was sufficient. I couldn't find it quickly but I did find this.

So maybe the bond is dependent on the epoxy itself, and proper prep, sufficient curing time, etc? I've been told by my supplier that some epoxy formulations produce less amine blush than others.
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Old 26-05-2020, 09:15   #14
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Re: Re-Gelcoating - How to deal with this crazing?

Quote:
Originally Posted by jhulmer View Post
It does remove it from the surface and is fine if painting. But, if putting Poly gel over epoxy it works for a while then the amine slowly works to the surface of the epoxy and will release the gel. This is the experience of the experts. Reading Minaret's post he points this out and he is a professional with the experience of it lifting.
You have to let it cure sufficiently to allow the bulk of the blush to come to the surface. I wait at least a week before gelcoat. Been laying fg decks and doing repairs for 15 years.
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Old 26-05-2020, 09:16   #15
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Re: Re-Gelcoating - How to deal with this crazing?

Quote:
Originally Posted by Lake-Effect View Post
There's a PDF from Gougeon Bros (WEST Systems) out there about some extensive tests of gelcoat over epoxy, which concluded that the bond was sufficient. I couldn't find it quickly but I did find this.

So maybe the bond is dependent on the epoxy itself, and proper prep, sufficient curing time, etc? I've been told by my supplier that some epoxy formulations produce less amine blush than others.
Amine is in the catalyst and yes they do make some with less and even no amine but you pay for it.
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