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Gell Coat cracks... Well the whole damn boat.

18321 Views 43 Replies 20 Participants Last post by  kidcarbon
So my boat is getting to the point where i want to rework the upper decks.

I have two problems , one is the boat is 40 years old and the gell coat has seen better days the second is that someone applied cheep paint over it and its cracking and flaking too.
So do i strip it down to glass and re do it all?
smooth it as much as possible and fill it?
or just go over it?

P.S. these holes are no longer there. I have redone them and they are the best spots on my deck as of now.

Thank you all for your time and for putting up with all my dumb questions.:)
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I had some of these problems on my boat and had been asked about this on a friend's boat. I ended up doing quite a bit of research; talking to repair yards, surveyors, and epoxy and paint manufacturers, and came to the following conclusions.

First of all, you need to determine why the cracking is occuring. If the problem is stress cracking, the underlying structural design issues need to be resolved before anything else is done. Then the cracks need to be dremeled out to solid laminate sealed with penetrating epoxy and filled with thickened epoxy resin.

If the cracking is the result of failing gelcoat then the cause and adhesion of the failing gelcoat needs to be investigated. If the cause is simply a matter of the gelcoat breaking down due to age, but the gelcoat is properly adherred the repairs are easier than if the gelcoat lacks adhesion. If the gelcoat lacks adhesion or is crumbling, then the gelcoat needs to be stripped down to solid laminate, a light layer of glass and epoxy laminated and then the deck faired and non-skid added. \

The good news is that in most cases the crazing is simply internal stresses in the gelcoat. That is especially prevelant in 1970's and early 1980's era boats.

After a lot of research I ended up deciding that MAS Epoxy offered the best solution for the problem. The following was the protocol that I ended up with for a boat that had severe crazing and which had previously had the decks painted and that paint was now failing as well.
  • Sand decks down to exposed gelcoat, removing all previously applied paint and fillers.
  • <O:pWash down with denatured alcohol to remove any sanding dust, grease or moisture. <O:p</O:p
  • Roll on a coat of MAS Low Viscosity resin, using MAS slow setting hardener, and adding 10% denatured alcohol to further thin the resin. <O:p</O:p
  • Add a second coat of MAS 'Flag resin', using the same slow setting hardener. <O:p</O:p
  • Order Flex-mold nonskid patterns from Gibco [email protected] and cut to shape of non skid areas. <O:p</O:p
  • Apply a thickened coating of resin, and then squeegee non-skid pattern into deck. Dye thickened resin to approximately match color of final finish. <O:p</O:p
  • Apply Awlgrip 545 primer- roll and tip<O:p</O:p
  • Apply final Awlgrip finish verifying current type of paint to use for decks with U.S. Coatings.
Subsequently, I have also spoken to Interlux. Interlux has a high build epoxy primer (epoxy resin based for use on epoxy laminate). This sounds like a better primer than the US Coatings (Awlgrip) product.

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You are correct that within the industry, companies like Interlux (International) and Epifanes recommend that their urethane products can be applied over scuffed, clean healthy polyester or vinylester gelcoat without a primer.

I have specifically discussed this with various reps and they have been consistent in this recommendation. If I were painting the topsides or cabinsides of an almost new boat, I would not expect the gelcoat to have been primed.

But this thread is a discussion of painting a deck with bad crazing problems. In my research process, as soon as I mentioned decks and crazing to the paint reps, all bets are off. Then they begin to hedge and caviat themselves very carefully. Typically, they will say that the gelcoat needs to be 'stabilized' in some form or removed.

It was here that each of the reps had their own recommendations. Some literally suggested stripping all gelcoat, laying a veil coat of glass and epoxy (or vinylester) and then using thier products to finish the job.

Others suggested reducing the thickness of the gelcoat rolling the deck with a very thin layer of a saturating epoxy, then coat with an epoxy based promer because epoxy resin was involved and urethane does not stick as well to epoxy resin as it does to polyester or vinylester resins.

And still others recommend simply cleaning and scuffing the gelcoat, roll out what is effectively an epoxy barrier coat, and the paint with their topcoat.

The reason that I mentioned MAS epoxy rather than some of the other brands is that MAS makes a penetrating epoxy specifically for these kinds of operations, and MAS does not produce an amine blush. In most cases the lack of amine blush is only a minor advantage but in the case of a deck, especially one that still has some texture remaining, it is not very easy to properly clean the amine blush from the resin, and so long term there may be adhesion problems that result from the remnant amine blush as the decks age and are exposed to heat.

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