Gelcoat issues

Questions about boat repairs with our resins and fiberglass: hull patches, transoms and stringers, foam, rot etc.
Mheltun
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Gelcoat issues

Post by Mheltun » Sun Apr 15, 2018 5:25 pm

Hello everyone and thanks for accepting me to your forum. Ive been restoring (well ,fixing up) a 1994 Parker 2320. I just finished with a roof recore and now ive been working on chip and crack repairs. For my repairs so far ive used epoxy. Now that the repairs are all finished ive started top coating with factory color matched gelcoat. The problem im now running into is the gelcoat will not cure (dry) direcly over the repairs. Ive even tryed using high build primer over the repairs and the gel still will not setup in areas (direcly over the epoxy). All other areas the gel sets up nicely. Ive observed all the ratios and my temps im working in are between 55-75 deg F. The humidity is low as well (inside a building). The gelcoat i have been using has the wax mixed in and ive also tryed covering the stubborn areas with PVA as well. Any help or advice is greatly appriciated.

Thanks,
Mark



DAYTRIP
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Re: Gelcoat issues

Post by DAYTRIP » Sun Apr 15, 2018 6:09 pm

First off ....gelcoat is a pain! My son and I build hatch and gutters and the single biggest issue is gelcoat related.

Is the stuff that is not curing from the same batch as the stuff that is curing? In other words when you catalyze a batch is some of it kicking and other not? Are you gelcoating over epoxy? Does heating it or putting it in the sun get it to kick? If you are going over epoxy I wonder if you are getting a blush that effects the gelcoat? You likely know it is not best practice the gelcoat ove4 epoxy but I have seen info that it will work. Maybe respond and I give you some more thoughts.

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Re: Gelcoat issues

Post by Fuzz » Sun Apr 15, 2018 6:13 pm

Hello Mark and welcome.
Not many folks around here use gelcoat so I am not sure how much help you will get. That being said I will tell the little I know. The amine in the epoxy does not play well with gelcoat and keeps it from curing. You need to make sure the epoxy is fully cured and then wash it with warm water and scrub it. Then coat the epoxy with a primer that is made for what you are trying to do. I do not know what primer you need but a little time with Google should give you an answer.

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Re: Gelcoat issues

Post by Fuzz » Sun Apr 15, 2018 6:25 pm

I posted at the same time as DayTrip. He has lots of experience with this sort of stuff so I would listen to what he has to say.

Mheltun
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Re: Gelcoat issues

Post by Mheltun » Sun Apr 15, 2018 7:51 pm

DAYTRIP wrote:
Sun Apr 15, 2018 6:09 pm
First off ....gelcoat is a pain! My son and I build hatch and gutters and the single biggest issue is gelcoat related.

Is the stuff that is not curing from the same batch as the stuff that is curing? In other words when you catalyze a batch is some of it kicking and other not? Are you gelcoating over epoxy? Does heating it or putting it in the sun get it to kick? If you are going over epoxy I wonder if you are getting a blush that effects the gelcoat? You likely know it is not best practice the gelcoat ove4 epoxy but I have seen info that it will work. Maybe respond and I give you some more thoughts.

The gel that is not curing is all part of the same batch. It’s the areas over the (primed) epoxy that won’t cure properly. The rest of the gel cures just fine. For example if I had a repair the size of a quarter done with epoxy I’m able to see the outline of the repair in the gelcoat, the “quarter” area is wet/tacky and the rest is fully cured. I had some concerns about blush as well so I wiped down the sanded epoxy with ammonia and water before priming then did the same on the primer before applying the gel. I have not tried heating the area yet and sunlight is not an option. I’m in northern Michigan and we have 30+” of snow on the ground and more falling 😡. Hindsight is always 20/20 and if I was to do it differently I would have used a poly resin. Consider me a rookie just trying to find my way.

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Re: Gelcoat issues

Post by DAYTRIP » Sun Apr 15, 2018 9:30 pm

It must be what fuzz outlined. Somehow you are getting blushing or a reaction with the epoxy. Might have to give the epoxy sometime to cure. Heat will excellerate it but don’t go nuts with that. I would let the epoxy cure for a week before you try to overcoat it. How long was the epoxy cured before you gel coated?

Mheltun
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Re: Gelcoat issues

Post by Mheltun » Sun Apr 15, 2018 10:14 pm

DAYTRIP wrote:
Sun Apr 15, 2018 9:30 pm
It must be what fuzz outlined. Somehow you are getting blushing or a reaction with the epoxy. Might have to give the epoxy sometime to cure. Heat will excellerate it but don’t go nuts with that. I would let the epoxy cure for a week before you try to overcoat it. How long was the epoxy cured before you gel coated?

The epoxy has had 2-4 weeks of cure time so far. The work has been carried out indoors with temps from 50-75 deg. I would guess majority of the time the temps are around 60deg. I sure do appreciate the feedback from you all. Hopefully I get this sorted out. One other clue and it may fit with the slow cure theory. On one of the first repairs I did I applied gelcoat after one week. The same problem occurred; no curing over the repair. I removed the gel and retryed a couple days later. The same thing happened again but the affected area was smaller. This time the gel over the edges of the repair (thinner) seemed to cure leaving only the thicker areas with uncured gel on top.

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Re: Gelcoat issues

Post by TomW1 » Sun Apr 15, 2018 11:41 pm

Epoxy and Gelcoat don't work well together. You need to apply a primer over the epoxy that works with the Gelcoat. That should solve your problem.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Mheltun
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Re: Gelcoat issues

Post by Mheltun » Mon Apr 16, 2018 6:47 am

TomW1 wrote:
Sun Apr 15, 2018 11:41 pm
Epoxy and Gelcoat don't work well together. You need to apply a primer over the epoxy that works with the Gelcoat. That should solve your problem.

Tom
Tom,

I agree and have heard the same thing. Before applying the gelcoat I did coat the repairs with a primer to hopefully avoid an adhesion issue.

silentneko
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Re: Gelcoat issues

Post by silentneko » Mon Apr 16, 2018 9:44 am

Just curious, but did you try adjusting the catalyst/MEKP? Just as a test I think I would first clean an area well, first water or alcohol then maybe acetone and let it dry, then I would add another 0.5% MEKP. You will know if it works within a few hours. I had issues with gelcoat curing correctly as the weather shifted before.
Built: 15ft Skiff, 16ft Skiff, Modified Cheap Canoe.....FS17 coming soon!

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