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Old 07-11-2021, 20:51   #1
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Gelcoat over epoxy undercoat?

Some further advice valued please...
Re"painting" my new (old) Cavalier 39 and considering doing the hull above the waterline in gelcoat rather than 2-part urethane, partly for cost reasons and partly for longevity reasons. I'm not too fussed about flashy finishes, etc.
I've got off all the topcoat but there is a slightly yellow/beige bottom coat that I'm sure must be epoxy - it doesn't budge for anything and I would have thought it was the gelcoat except that I can see the odd spot where it has been painted over a previous topcoat, and when I sand it off it gets into the white gelcoat.
Do I have to get off this epoxy layer before gelcoating? Or can I give it a good sanding and apply the gelcoat over the top of it?
I was thinking of applying the gelcoat by roller.

Cheers!
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Old 08-11-2021, 05:02   #2
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Re: Gelcoat over epoxy undercoat?

Applying Polyester Gelcoat over Epoxy
https://www.epoxyworks.com/index.php...at-over-epoxy/

See also ch. 15.3 Finish coatings ➥ https://www.westsystem.com/wp-conten...anual-2015.pdf
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Old 08-11-2021, 05:19   #3
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Re: Gelcoat over epoxy undercoat?

If you are okay with a white finish, I recommend to first use Awlgrip 545 primer for one (or two if you want a nicer finish) coats, followed by 2-3 coats of original Awlgrip topcoat.

The reason for white is that you can just roll it on, without tipping. The reason to do this instead of gelcoat: this lasts longer, is less work and looks better after the first year.

It does require cartridge respirators for rolling because it’s poisonous before curing.
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Old 08-11-2021, 05:22   #4
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Re: Gelcoat over epoxy undercoat?

Jedi has the right answer here.
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Old 08-11-2021, 06:23   #5
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Re: Gelcoat over epoxy undercoat?

Quote:
Originally Posted by JeremyFowler View Post
Some further advice valued please...
Re"painting" my new (old) Cavalier 39 and considering doing the hull above the waterline in gelcoat rather than 2-part urethane, partly for cost reasons and partly for longevity reasons. I'm not too fussed about flashy finishes, etc.
I've got off all the topcoat but there is a slightly yellow/beige bottom coat that I'm sure must be epoxy - it doesn't budge for anything and I would have thought it was the gelcoat except that I can see the odd spot where it has been painted over a previous topcoat, and when I sand it off it gets into the white gelcoat.
Do I have to get off this epoxy layer before gelcoating? Or can I give it a good sanding and apply the gelcoat over the top of it?
I was thinking of applying the gelcoat by roller.

Cheers!
Are you sure it's epoxy? Something seems a little odd here; why would someone put epoxy over an existing paint, and then paint over that with another topcoat? Why would epoxy yellow, which is usually caused by UV exposure, whilst under a topcoat?

I'd attempt to ensure that the 'problem coat' is, in fact, epoxy, and, if it is, follow the directions linked to by Gord.

At 250/gallon for Awlgrip, not counting the primer, I'd say polyester gelcoat is a very good alternative; 1 coat of 60.00 gelcoat versus at least 3 coats of 250.00 Awlgrip product yields something like a 15 x cost saving on materials alone.
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Old 08-11-2021, 06:36   #6
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Re: Gelcoat over epoxy undercoat?

Oops. I should have included one more thing. Jim has a good point about the cost. If you were looking to save cost, lots of paints will work.

I painted my dagger boards very quickly. In fact, I didn’t even paint them. Somebody who has never painted anything before painted them during the launch of my boat.

There was no more good paint left. My boat was painted in Imron And I was out of it. But it was launch day so we had to do something. I didn’t want the sun damaging the epoxy the boards are made out of.

So off to Home Depot to grab some exterior semi gloss white paint, brushes and rollers. I used no primer. The person who painted it had never painted anything before. I figured that would be OK to keep the sun off them for a few months.

As it turns out, the paint stuck perfectly to the epoxy, with a couple coats it hid everything. And here it is something like five years later in the harsh Florida sun and it still looks the same as it did when it was done. I am astounded. The kind of paint you use has almost nothing to do with the longevity. Has a lot more to do with the shine and gloss. So, if you don’t care about looks, Home Depot exterior paint is not such a bad thing. It will last and protect.
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Old 08-11-2021, 06:37   #7
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Re: Gelcoat over epoxy undercoat?

The recommended undercoat if painting with 2k polyurethane is epoxy, however it's usually spec'd as high build which is very easy to sand and no doubt has a surface more suited to allowing top coats to mechanically bond. The logic for using epoxy is that it sticks like poop to a blanket and is less likely to fry the old gelcoat and polyurethane sticks to it well. It's possible perhaps that a po used the same epoxy spec used to barrier coat the underwater section of the hull for the topsides?



If you do roller apply gelcoat (which by that you really mean flowcoat which is gelcoat with added wax to aid curing) you will probably regret it in short order as the finish will be rough because, despite the name, it doesn't flow that well and it is a major, major, major task to wet sand it all smooth when done. I'd be inclined to prep, re-undercoat and paint in a 2k system as recommended for the application by a trusted local supplier. I'll add that doesn't necessarily mean using overpriced specialty yacht paints, as many industrial products are suitable. Personally, I've used off the shelf 2k industrial polyurethane. It goes on easy, dries quick (no dirt and bugs - that won't be the case with flowcoat) can be repaired and can be polished with fibreglass polishing products as it dulls with age. About the only downside is don't use it for underwater applications as it can develop small blisters.
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Old 08-11-2021, 09:29   #8
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Re: Gelcoat over epoxy undercoat?

Quote:
Originally Posted by Reefmagnet View Post
I'll add that doesn't necessarily mean using overpriced specialty yacht paints, as many industrial products are suitable.
I agree with not using gelcoat, and if you're not after a mega-millions yacht finish their are industrial coatings that work exceptionally well for a more "practical" finish at far less expense.
PPG makes some great stuff; https://us.ppgrefinish.com/PPG-Refin...tings/Amercoat
I've used a lot of this over the years on various jobs;http://www.amersun.com.sg/235_PDS_AI.pdf and it works quite well, without being "fussy" like so many other products.
PPG also has both 1 and 2 part top-coat products.
The PDF file doesn't list wood or fiberglass application, but not to worry, it sticks/works just fine.
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Old 08-11-2021, 12:14   #9
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Re: Gelcoat over epoxy undercoat?

as a thought... are you sure its epoxy?... I used a poly paint one time and had a devil of a time trying to remove it (later)... left me an epoxy fan
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Old 08-11-2021, 14:35   #10
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Re: Gelcoat over epoxy undercoat?

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as a thought... are you sure its epoxy?..
It says so on the PDF; "Multi-purpose epoxy coating -".
It is available in both "Low VOC", for some states, and the more normal formulation.
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Old 08-11-2021, 14:54   #11
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Re: Gelcoat over epoxy undercoat?

Epoxy topcoats are entirely different from epoxy undercoats in characteristics from my experience with them. Top coats are really sticky to apply and actually do feel like you're painting with glue. Once hardened, the gloss is good and they are hard and resistant to just about everything except uv light. . Perfect paint for bilges and lockers.
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Old 08-11-2021, 15:09   #12
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Re: Gelcoat over epoxy undercoat?

Perhaps I've not been clear enough in my descriptions of PPG products.
The Amercoat 235 is an Epoxy Primer.
Their are other "paint/product numbers" that identify a range of both 1 and 2 part products,, both in Primers and Topcoats.
It's a large product range, but most of my using has been the "235", I mostly use it as a "high build" under the Interlux Prime-Coat, which is not as heavy-bodied, but have also applied both 1 and 2 part topcoats directly over it.
Once it cures it sands quite nice.
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Old 08-11-2021, 15:22   #13
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Re: Gelcoat over epoxy undercoat?

General old salt wisdom is not to put any polyester or gelcoat over epoxy. It can be done, especially in small repairs, but I would still say avoid that in a whole boat repaint.

But I would try to figure out if it really is epoxy. Brown in color means nothing. the fact that it is so hard, may mean it is epoxy. I'm not sure if there's a DIY chemical test you can do???

Total boat makes both 1-part and 2-part top coat paints that don't require tipping for as little as $99 a gallon. There are many others. I suspect paint will be much easier to apply and get a good finish than gelcoat, but will likely cost more. My Imron looks good at 15 years, but it's $$$.. Shop around for paint.
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Old 08-11-2021, 15:35   #14
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Re: Gelcoat over epoxy undercoat?

Quote:
Originally Posted by Bowdrie View Post
Perhaps I've not been clear enough in my descriptions of PPG products.
The Amercoat 235 is an Epoxy Primer.
Their are other "paint/product numbers" that identify a range of both 1 and 2 part products,, both in Primers and Topcoats.
It's a large product range, but most of my using has been the "235", I mostly use it as a "high build" under the Interlux Prime-Coat, which is not as heavy-bodied, but have also applied both 1 and 2 part topcoats directly over it.
Once it cures it sands quite nice.

From the OP's perspective I suspect that someone may have used either an epoxy topcoat or barrier paint instead of high build for an undercoat. Especially as the they seem unhappy with the current paint on the boat which is odd if it was done with a decent 2k paint as, arguably, that is as good as a gelcoat finish if done correctly and should probably be expected to last around a decade or so with minimal care. Polyurethane can get a bit chalky on the surface after a few years, but this can be buffed out.
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Old 09-11-2021, 02:02   #15
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Re: Gelcoat over epoxy undercoat?

Question of paint vs gelcoat is well discussed in this TrawlerForum thread. If you skip to #18, quoted text from Steve D'Antonio strongly advises paint over gelcoat.

https://www.trawlerforum.com/forums/...d.php?p=827650

[I] "While I continue to encounter this, gelcoat vs. paint, question from time to time, it continues to surprise me. In short, other than for repairs, gelcoat is best suited for use in a mold, i.e. it is applied to the inside of a female mold first, then fiberglass fabric and resin are applied on top of it, before the gelcoat is fully cured, thereby creating a very tenacious, chemical bond between the two."
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