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Gelcoat on Epoxy: Will it work, or disaster?


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So I've got a patch of deck to repair, and have to decide on the method.

The West literature claims that gelcoat will stick to epoxy.  Standard industry wisdom says this is like crossing the streams in the movie Ghostbusters.  Who is right?

I do admit a few years back I filled some un-used screw holes with epoxy and then put gelcoat over top of it, worked fine - but a tiny repair, not under stress.  This is some core repair, smooth area (not anti-skid).  About a square foot.

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1 hour ago, Zonker said:

Wash the cured epoxy well with warm water and a green scrubby. The residual amine on the surface is what seems to inhibig the Gelcoat cure. 

My experience is it cures and looks fine but in a few to 6  months its starts to fail

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10 hours ago, Zonker said:

Wash the cured epoxy well with warm water and a green scrubby. The residual amine on the surface is what seems to inhibig the Gelcoat cure. 

Peel ply is my friend.  And vacuum bagging.  But yes, any exposed epoxy gets the water wash with the scrubby pad.

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when you remove the peel ply you are removing the amine when you sand you remove the amie. gelcoat over epoxy or polyester works best if there is a lot of tooth for it to hold on to. I use 80 grit before gelcoat. there are additives the make gelcoat adhere to epoxy better. I have used Duratec and it works good it also thins the gelcoat for spraying but does make the color a bit more see thru.

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Thanks Gouv!

So - remove amine, 80 grit prep, possibly "duratec".  And faith.

Well, it isn't structural and worst case it looks bad for a season, I guess I will go for it.

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Really, really, really (yes really) scrub to remove the amine blush. I have had significant issues due to amine causing the gelcoat not to harden. I might think about using a non-blushing epoxy as well if it makes sense for the type of repair. 

Other than that, it can work pretty well. 

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Wash it down with water, water only. I wipe first with cloth towel and warm water to remove most of the blush. You can feel the surface difference right away. Next, scrub with a soft scrub pad. Then sand with 80 grit without goofball kneeling to the gel coat gods or leaps of faith. It simply works and if done properly will not fall off in 6 months.

 Mixing Duratec additives works beautifully but that doesn't answer the gel coat over epoxy question. I was a disbeliever and never bought into the water only blush removal, until I actually tried it. Do not use soapy water. Nice clean bottled drinking water works great.

 No blush epoxy is a bad alternative imho.

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The most amazing thing about those pushing application of polyester over epoxy are generally the same folks who insist Epoxy over old polyester is “better because of the epoxy’s super duper adhesive properties. 

Counting on adhesion when applying polyester over well cured epoxy is an invitation to Mr Murphy to show up.

The failure to adhere is NOT 100% ABOUT AMINES.

There are a myriad of reason the bond snd / or the cure can fail to happen as you wish

You may be working on your own boat where the consequences of surprise failures are nothing more than an opportunity to enjoy working on your own toy. 

Those of us who sell our services to other people have two options:’

**Do it properly so it lasts until we die.

**Not do it at all. 

I haven’t knowingly applied polyester over epoxy this century. I have no intention of ever doing do again. 
 

If a person employed in my  shop is caught deliberately applying polyester over epoxy he is given three days off unpaid or fired on the spot.

 It is an offense  that ranks up there  with applying epoxy over antifoulant , applying hard antifoulant over ablative, using non-stainless fasteners,  stealing beer or alcohol from a customer’s boat, or other absolutely  inexcusable  bullshit. . 

 

 

.

 

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21 hours ago, Gouvernail said:

The most amazing thing about those pushing application of polyester over epoxy are generally the same folks who insist Epoxy over old polyester is “better because of the epoxy’s super duper adhesive properties. 

Counting on adhesion when applying polyester over well cured epoxy is an invitation to Mr Murphy to show up.

The failure to adhere is NOT 100% ABOUT AMINES.

There are a myriad of reason the bond snd / or the cure can fail to happen as you wish

You may be working on your own boat where the consequences of surprise failures are nothing more than an opportunity to enjoy working on your own toy. 

Those of us who sell our services to other people have two options:’

**Do it properly so it lasts until we die.

**Not do it at all. 

I haven’t knowingly applied polyester over epoxy this century. I have no intention of ever doing do again. 
 

If a person employed in my  shop is caught deliberately applying polyester over epoxy he is given three days off unpaid or fired on the spot.

 It is an offense  that ranks up there  with applying epoxy over antifoulant , applying hard antifoulant over ablative, using non-stainless fasteners,  stealing beer or alcohol from a customer’s boat, or other absolutely  inexcusable  bullshit. . 

 

 

.

 

Bullshit!! You are clueless.

Sometimes, your inane rants are hilarious because they are so far out in left field. That collection of words is far from constructive. It's mean spirited ignorance at best and it's nonsense.

 OP asked a question. Some replied with working solutions to his question. You........typed bullshit as usual.

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1 hour ago, PeterRoss said:

Bullshit!! You are clueless.

Sometimes, your inane rants are hilarious because they are so far out in left field. That collection of words is far from constructive. It's mean spirited ignorance at best and it's nonsense.

 OP asked a question. Some replied with working solutions to his question. You........typed bullshit as usual.

The OP asked if gelcoat will stick to epoxy, Gouvernail is just saying that as a professional he can't take that risk which I totally get.
For what its worth none of the professional repair guys around here will put gelcoat over epoxy either, and they all subscribe to his philosophy that in nearly all cases a repair in Polyester is perfectly adequate. 

 

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1 hour ago, MiddayGun said:

The OP asked if gelcoat will stick to epoxy, Gouvernail is just saying that as a professional he can't take that risk which I totally get.
For what its worth none of the professional repair guys around here will put gelcoat over epoxy either, and they all subscribe to his philosophy that in nearly all cases a repair in Polyester is perfectly adequate. 

 

 He takes risks everytime he touches a boat. Your comment about polyester does not apply. OP noted epoxy was used some time ago. 

 In his case there is nothing wrong with gel coat over epoxy. Any "Professional" who runs away from that repair due to inexperience uses the term "Professional" lightly.

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On 12/18/2021 at 11:36 PM, sculpin said:

So I've got a patch of deck to repair, and have to decide on the method.

The West literature claims that gelcoat will stick to epoxy.  Standard industry wisdom says this is like crossing the streams in the movie Ghostbusters.  Who is right?

I do admit a few years back I filled some un-used screw holes with epoxy and then put gelcoat over top of it, worked fine - but a tiny repair, not under stress.  This is some core repair, smooth area (not anti-skid).  About a square foot.

If the boat is made of vinylester, just use that to fix it and no worries.

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@10ton - a couple of reasons.

One being the possible myth that new vinylester won't stick well to 40 year old vinylester, the other being that I haven't worked much with it - I've literally gone through dozens of gallons of west, vacuum bagging stuff, but have only done minimal stuff with the other.

I'm more worried about the repair being strong than I am about gelcoat, so I am leaning towards epoxy and putting on gelcoat, if it fails I can just sand it off, re-fair, and paint.

The repair is replacing core around the mast opening in the deck, I've got to cut it open, dig out the mush, slap in some coosa board, and glass it closed again.  I _may_ be able to do it from underneath.

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21 hours ago, sculpin said:

@10ton - a couple of reasons.

One being the possible myth that new vinylester won't stick well to 40 year old vinylester, the other being that I haven't worked much with it - I've literally gone through dozens of gallons of west, vacuum bagging stuff, but have only done minimal stuff with the other.

I'm more worried about the repair being strong than I am about gelcoat, so I am leaning towards epoxy and putting on gelcoat, if it fails I can just sand it off, re-fair, and paint.

The repair is replacing core around the mast opening in the deck, I've got to cut it open, dig out the mush, slap in some coosa board, and glass it closed again.  I _may_ be able to do it from underneath.

An expert craftsman repaired my 30yo vinylester boat with… vinylester. Repair done in late 2015, most of the bow was re-fabricated, and it hasn’t fallen off. He used thickened gelcoat to fair the repair, btw.

His advice: ‘if someone else hits you, try to take it on that bow.’

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7 hours ago, Max Rockatansky said:

An expert craftsman repaired my 30yo vinylester boat with… vinylester. Repair done in late 2015, most of the bow was re-fabricated, and it hasn’t fallen off.

He must have used the good cardboard and cello tape.

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@SloopJonB since you need to have it explained to you, here’s the thing:

anything said by a high-post-count internet hack, (and that is you), counts exactly nothing against the advice given by the craftsman who was born into a family of boat builders, built and repaired boats literally all his life, and who also is regularly flown to high-level regattas to work on boats.

I understand that you may be upset by the news that you are an internet hack. I will place you in my ignore list and you should in return put me in yours.

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On 12/23/2021 at 2:01 PM, blurocketsmate said:

I've gelcoated over epoxied repairs with no issues, at least for a couple of years, after which I lost touch.

^ this ^

Yes  to washing/scrubbng off the amine blush OR using peel ply. Yes to giving the surface some "tooth."

But I don't go to the trouble any more, I just hit it with the closest color I can find in a rattle-can and fade the spray in to match the rest. Someday I'll refinish the whole thing.

I gave up on trying to make boats PERFECT. Now I just want them to be 1- better than before, probably better than new; and 2- last 10% longer than I'm likely to be using the boat. 'Master Crafstmen' can kiss my ass, I've been fixing your shit for 50+ years now.

- DSK

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4 hours ago, Max Rockatansky said:

@SloopJonB since you need to have it explained to you, here’s the thing:

anything said by a high-post-count internet hack, (and that is you), counts exactly nothing against the advice given by the craftsman who was born into a family of boat builders, built and repaired boats literally all his life, and who also is regularly flown to high-level regattas to work on boats.

I understand that you may be upset by the news that you are an internet hack. I will place you in my ignore list and you should in return put me in yours.

Max, mate..... you totally missed the joke about the repair to your bow, that didnt fall off, being done with the good cardboard and celo tape......  

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1 hour ago, Steam Flyer said:

Yes  to washing/scrubbng off the amine blush OR using peel ply. Yes to giving the surface some "tooth."

But I don't go to the trouble any more, I just hit it with the closest color I can find in a rattle-can and fade the spray in to match the rest. Someday I'll refinish the whole thing.

That's all I did. The boat wasn't that old, so the factory gelcoat still matched perfectly. I'm not sure what I would have done otherwise - probably still gelcoat, doing my best to match it, as that's what I was used to working with.

No peel ply, just plastic wrap, sanding, then another coat, sanding, then buffing or whatever.

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49 minutes ago, basketcase said:

Max, mate..... you totally missed the joke about the repair to your bow, that didnt fall off, being done with the good cardboard and celo tape......  

Even after I pointed that out he didn't get it.

Maybe with your elaboration it will get through.

I particularly enjoyed his comment that I needed it explained to me. :lol:

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7 hours ago, Max Rockatansky said:

two things:

i gat better shit to do with my time (and bandwidth) than keep up with the latest meme or vid or whatever, so no, I missed that, I happily admit

Regardless, it was a slag on my statement, why should I not defend?

Max, mate..... the front fell off is one of those sa things, almost as old as hwsnbn, void ho or fuck off newbie. I am pretty sure, based on that, it was not a slag.

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It wasn't a slag. This is one of those "if you're a hammer ..." deals. A brief break from the white noise is an easy fix, and saves on bandwidth. Turns out that the internet sucks in comparison to a cockpit chat.

As an experienced sailor out there doing it, the forum needs you in good form, Cap. 

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I've done lots of work with vinylester making racecar bodywork.  It's quite easy to use, relatively strong, significantly cheaper, and you don't have any dissimilar material issues with gelcoat.  

You can then use chopped mat if you want , but you need the "ester" as the binders in the mat are dissolved by it...

 

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On 12/19/2021 at 12:38 AM, SloopJonB said:

The Gougeons practically invented marine epoxy.

Think there's anyone who knows more than them about it?

 

On 12/27/2021 at 11:07 AM, basketcase said:

and that worked out really well on the G32s they built.......

In that case it was the epoxy not bonding to the gelcoat rather than the other way around.

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On 12/19/2021 at 12:38 AM, SloopJonB said:

The Gougeons practically invented marine epoxy.

Think there's anyone who knows more than them about it?

Sorry, they were far from the inventors of marine epoxy, just very good at marketing.

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13 hours ago, Steve said:

Sorry, they were far from the inventors of marine epoxy, just very good at marketing.

Actually, I think they were. With the help of chemists, of course.

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They were certainly the developers of a large number of the now standard processes for using the stuff.

I got a first edition of their book over 40 years ago at the PT Festival and it was full of info that "nobody knew about" at the time.

Not just about epoxy but lots of tips & tricks for lightweight wood construction and so forth.

AFAIK they were pretty unique in that they tested various methods and material combinations to destruction to get fundamental specs for epoxy laminate construction.

Epoxy for laminated wood big boat construction was still pretty new at the time - prior to them most big boats were laminated using resorcinol and other, lesser adhesives.

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On 1/10/2022 at 9:08 AM, Russell Brown said:

Actually, I think they were. With the help of chemists, of course.

Nope, maybe in the US but Ciba Giegy, Epiglass and probably a few  others were in regular use in other parts of the world in the marine industry decades before west systems amateur chemistry set came on the scene.

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Araldite, by Ciba-Geigy was my first use of epoxy resin in boat building in the 1960’s.

not sure when Gougeons started playing.?  Anybody?
 

The first batches of Araldite epoxy resins, by which the brand is most well known for, were made in Duxford, England in 1950.[1]


 

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The fact that the Brits were glueing small bits of wood together with Araldite , to build Mosquito bombers in the 1940s wouldn’t have gone un noticed.

Posibly  not branded as such remembering the Araldite brand originated from Aero Research Limited. ARL.

ARL we’re bonding metals etc with epoxy long before it was popularised in boat building guides.

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i would no more read as gospel a 40 ( or even 20 ) year old book on epoxy

than i would the same age books on gelcoat or indeed any surface coating

 

to be fair .. there are still some similarities between epoxy made 40 years ago and epoxy made now

... not many though

formulations change over time ( a lot ) but well respected product names ..  not so much

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The Gougeon book on boatbuilding is still a useful reference as long as you are capable of reading between the lines and realize that everything in there is geared toward consuming as much epoxy as possible, it is first and foremost a marketing tool for their products.

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1 hour ago, Steve said:

it is first and foremost a marketing tool for their products.

That can be said about any information from any material manufacturer ...

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Talk about thread drift...

I think the bottomline from all of this:

You possibly can put gelcoat over epoxy if you remove the blush and give it a good rough surface to adhere to.  Proceed at your own risk.

But generally speaking, if the original area was polyester or vinylester based, then a properly executed repair with vinylester will be as strong as the original without the dissimilar material issues, and potentially at lower cost.

does that about sum it up?

 

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Epic thread drift, who'd have predicted that.

Anyway.  I am going to go ahead with gelcoat over epoxy.  I'm most comfortable making the repair in epoxy as I do lots with it already and so am confident of work time, vacuum bagging, etc.  Thanks all, interesting discussion.

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