Gelcoat over Epoxy

woodpecker

Member
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81
I am trying to fix some gelcoat chips on an epoxy boat. I am having problem with the gelcoat drying.

I have tried using duratec  (50%) and then spraying PVA over it. 2% MEKP. Also tried a little heat.

Still tacky after a couple of days.

I know Polyester and Epoxy don't meld well.

Any suggestions?

Should i put some sort of primer first?

 
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phill_nz

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what temperatures are around when you are doing it

try a little in a cup at ~20c at 2% it should gel around 8-12 mins depending on age and season it was made

if its outside ( longer ) than that range it may have drifted to far to use reliably

do the test and get the results back before we can go further

i have never used any type of barrier on my gelcoat repairs

just slightly overfill and carve off most of the excess with a razor blade when firm gel and 600 wet n dry when hard gelled before total cure stage

a hand rub with metal polish or cut n polish after than brings to usable and should be unnoticeable if the colour is right

 

woodpecker

Member
496
81
what temperatures are around when you are doing it

try a little in a cup at ~20c at 2% it should gel around 8-12 mins depending on age and season it was made

if its outside ( longer ) than that range it may have drifted to far to use reliably

do the test and get the results back before we can go further

i have never used any type of barrier on my gelcoat repairs

just slightly overfill and carve off most of the excess with a razor blade when firm gel and 600 wet n dry when hard gelled before total cure stage

a hand rub with metal polish or cut n polish after than brings to usable and should be unnoticeable if the colour is right


Thanks, It kicks of fine in the pot but just wont dry where it goes over the epoxy. Where is goes over the old gel coat is drys fine.

Thinking there is a reaction between the epoxy and the polyester. BTW all the materials are fresh.

 
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Rain Man

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I have had gelcoat behave like this in the presence of cool temperatures and moisture.  I had no choice but to leave it and pray it would eventually go off - if it didn't I was going to remove it.  After about a week in the sun it did.  

 

casc27

Super Anarchist
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The tackiness has nada to do with the curved epoxy under it.   It's simply not curing.   Make sure to wash/sand/clean the epoxy prior.
Wash it, wash it thoroughly before any sanding. If not you just grind the amine blush into the substrate and it is really tough to wash it completely clean after that. 

 

woodpecker

Member
496
81
It would not cure where I used Epoxy filler to fair before Gel coat. Cured fine everywhere else.  The reason I used epoxy as it is an epoxy boat. I ground it all out and used polyester fairing. Let see what happens.

The guys at Total boat told me I can't put Gel coat over their epoxy filler as it won't let the Gelcoat cure. 

Here is a link to what they described. (Scowl down thru it)

https://www.jamestowndistributors.com/product/epoxy-and-adhesives/fairing-compounds-and-repair-putties?trk_msg=QMM7BQFJQBNKH6K4FJMAEHB3CC&trk_contact=OPSVM481ASFK382NCMN4FO8IVS&trk_sid=VQO36GT50G8EBF5I28TGQT5DQ4&trk_link=P1V49LMI205KR1B220S98VKCU8&utm_source=listrak&utm_medium=email&utm_term=Fairing Compounds Explained&utm_campaign=Weekly Feature - November 2021&utm_content=Epoxy vs Polyester Fairing Compound

 

DRDNA

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Ventucky
I only have luck gel coating over epoxies that are 5:1 mixes.  Any others, like 1:1, 2:1, etc. have been a no go.  Also , I have to let the epoxy cure a lengthy time, scrub the crap out of the epoxy with water, and often times I put a thin layer of vinyl ester resin over the cured epoxy before applying gel coat.  Best of luck.

 

woodpecker

Member
496
81
I only have luck gel coating over epoxies that are 5:1 mixes.  Any others, like 1:1, 2:1, etc. have been a no go.  Also , I have to let the epoxy cure a lengthy time, scrub the crap out of the epoxy with water, and often times I put a thin layer of vinyl ester resin over the cured epoxy before applying gel coat.  Best of luck.
5:1   = Gelcoat/Duratec? Or vice versa?

 

Raz'r

Super Anarchist
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I only have luck gel coating over epoxies that are 5:1 mixes.  Any others, like 1:1, 2:1, etc. have been a no go.  Also , I have to let the epoxy cure a lengthy time, scrub the crap out of the epoxy with water, and often times I put a thin layer of vinyl ester resin over the cured epoxy before applying gel coat.  Best of luck.
I will say the one repair where I had gelcoat over epoxy/glass, was a "straight from the West book" deal - west system epoxy, scrubbed, sanded, gelcoated including a cast of the non-skid, and polish.

Worked fine. Never tried with a 2:1

 

Gouvernail

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You can only make gelcoat cure properly over epoxy by using a primer such as Unobtanium 12 or if you are wrong about it bring epoxy actually applying over a polyester substrate. 

 

40grit

Anarchist
At my shop, we have encountered these failures. From experience, the epoxy chemistry affects cure. Especially fresh epoxy substrate. 
We have found, after failures have been cleaned up, a second coat has no more problems. 
 

 
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