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Old 03-04-2014, 06:36   #1
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Polyester Flowcoat stick to Epoxy?

My anchor locker has a flat floor, with the topmost layer being an epoxy-resin based laminate layer.

The surface has been hammered by anchors and chain over time, and I want to lay down a layer of polyester flowcoat to make it smooth and easier to clean.

Normal paint is too thin to be able to smooth out the dents and dimples in there, so I want to use my flowcoat which lays down nice and thick.

It has been stated on this forum that, in general, polyester resin does not stick well to epoxy laminate.

Question: Will polyester flowcoat stick acceptably to an (old) epoxy laminate?
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Old 03-04-2014, 07:33   #2
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Re: Polyester Flowcoat stick to Epoxy?

I have never had problems putting gelcoat over epoxy. Just key the epoxy up very well and apply. Everyone else here seems to have the complete opposite opinion of this, although I don't know about their actual experience with doing it.

Flowcoat will not smooth out dents and dimples. You will need to fill them first. Flowcoat is just gelcoat with wax added and is usually a bit thinner than normal laminating gelcoat.

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Old 03-04-2014, 08:07   #3
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Re: Polyester Flowcoat stick to Epoxy?

I've had varying success--it worked fine inside the boat, but on the transom outside the flowcoat cracked and peeled after about 5 years in the sun.
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Old 03-04-2014, 08:16   #4
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Re: Polyester Flowcoat stick to Epoxy?

I have used vinylester resin/glass over West System epoxy without problems. I abbrated the surface well and washed off the amine blush, of course. West system itself say's it's OK to use gelcoat over epoxy if prepared properly. Now where strength of bond is critcai epoxy is the resin to use. This would be the case where sheer force is the primary force. I wouldn't bond something to a verticle surface with polyester.
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Old 03-04-2014, 08:26   #5
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Re: Polyester Flowcoat stick to Epoxy?

You can get thick epoxy that is self-leveling, used for bar tops for example, and will stick to almost everything and is shiny smooth. Can add pigment to give it some color.
Epoxy :*Epoxy Resins and Hardeners
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Old 03-04-2014, 09:49   #6
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Re: Polyester Flowcoat stick to Epoxy?

Stick with epoxy. You can easily control the consistency with fillers/additives, and the color with pigments.
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Old 03-04-2014, 17:23   #7
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Re: Polyester Flowcoat stick to Epoxy?

Several posters above advise against using polyester flowcoat over epoxy laminate. May I just clarify, you are saying that the flowcoat will not stick but just "flake off" within a year or so ?
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Old 03-04-2014, 19:08   #8
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Re: Polyester Flowcoat stick to Epoxy?

We're saying that the general rule is:
Epoxy over polyester=OK.
Polyester over epoxy=NG.

Epoxy is generally more flexible.
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Old 03-04-2014, 20:44   #9
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Re: Polyester Flowcoat stick to Epoxy?

Quote:
Originally Posted by Marqus View Post
My anchor locker has a flat floor, with the topmost layer being an epoxy-resin based laminate layer.

The surface has been hammered by anchors and chain over time, and I want to lay down a layer of polyester flowcoat to make it smooth and easier to clean.

Normal paint is too thin to be able to smooth out the dents and dimples in there, so I want to use my flowcoat which lays down nice and thick.

It has been stated on this forum that, in general, polyester resin does not stick well to epoxy laminate.

Question: Will polyester flowcoat stick acceptably to an (old) epoxy laminate?


Definitely no. But you can tie coat. My preferred tie coat is 545, it ties almost everything. If you are just trying to fill imperfections, just slick it with some epoxy and 407 once and sand it out before applying coatings. It'll be faster in the end (though not as fast as if you could use poly products without tie coating).
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Old 03-04-2014, 21:09   #10
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Re: Polyester Flowcoat stick to Epoxy?

In this article the West System epoxy people tested the strength of various epoxy to polyester bonds, including gelcoat over epoxy.

To a dried, 100% cured substrate, the gelcoat bond is mechanical, regardless of whether the substrate is epoxy or polyester. So the substrate must first be completely cured, then be properly degreased, no amine blush, then properly roughened before gelcoat is applied.
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Old 03-04-2014, 21:16   #11
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Re: Polyester Flowcoat stick to Epoxy?

Lake--good info.

They say "Our test clearly demonstrates that polyester gelcoat will bond to a properly prepared WEST SYSTEM epoxy as well as to a cured polyester laminate. This test confirms that polyester gelcoats can be applied over cured WEST SYSTEM epoxy on repairs below the waterline."
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Old 03-04-2014, 22:07   #12
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Re: Polyester Flowcoat stick to Epoxy?

Good to know.
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Old 04-04-2014, 03:18   #13
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Re: Polyester Flowcoat stick to Epoxy?

Quote:
Originally Posted by minaret View Post
My preferred tie coat is 545, it ties almost everything.
I'm on a good learning curve here. This "Tie Coat" paint sounds pretty handy for many potential situations.

Just wondering how Tie Coats work.

How does it bond the two layers that are being tied - is it a chemical bond? Does the top coat, in this case polyester flowcoat, go on to tie coat and chemically bond with it?

If not, then what makes the bond?
I assume you don't roughen up the Tie Coat after application, so it's probably not a mechanical bond.
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Old 04-04-2014, 07:43   #14
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Re: Polyester Flowcoat stick to Epoxy?

Awlgrip 545 is a 2-part epoxy primer. It is the same basic chemistry as your current epoxy build, so I don't understand why Minaret thinks that epoxy is OK for use under polyester gelcoat but your current epoxy is not.

The primer will be a mechanical bond and you will need to sand it before gelcoat. Since you have old epoxy that will be difficult to really clean well, and you need to do some filling anyway, an epoxy primer like this is a good idea to give the gelcoat a new clean keyed surface to adhere to.

If you read the post threads again, you will find only two people saying you cannot put gelcoat over epoxy - only one of which seems to actually have experience doing so. The rest of us have related direct experiences of having no issues. Including an epoxy manufacturer.

But if you are still concerned, then nimblemotor has your answer - just use tinted epoxy. Epoxy does not tint as well as gelcoat, but for use in an anchor locker that should not be an issue. I wouldn't use the tabletop stuff he recommends, though.

Your other option is to just fair it out with a couple passes of slightly thickened epoxy and paint it.

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Old 04-04-2014, 07:52   #15
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Re: Polyester Flowcoat stick to Epoxy?

If you are doing repairs on the exterior remember that, epoxy, however tinted, is going to turn brown in the sun.
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