Epoxy, Gel Coat, Bondo, fiberglass repair - Fiberglass RV

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Old 12-03-2011, 11:45 PM   #1
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Name: kevin
Trailer: 13' Scamp
Posts: 170
Epoxy, Gel Coat, Bondo, fiberglass repair

I started with a simple project and it has gotton more and more miserable due to incomplete information here and in a bunch of marine forums. All I wanted to do was to repair a few minor gel coat chips as shown in the picture. So I happily set off chipping off all the loose gel coat to find that there was actually a large void under the gel coat. This is not uncommon with Scamps and is due to improper building technique that allowed air to remain trapped under the fiberglass when it was applied to the mold.

Once I removed all the gel coat that would come off easily with a scraper, I then ground the entire area down with the flap sand paper attachment on my grinder for a nice surface to fill. When choosing filler I did a lot of research on this site and others. A lot of people here have had luck with glass filled Bondo filler. All the information on marine forums said "DO NOT USE BONDO" because of issues with water absorption. Therefore I used West System Epoxy based on a recommendation from some people here and boat people love that stuff. I mixed in the colloidal silica filler until it was a nice peanut butter consistency and filled the void. Three layers later of epoxy I had a perfect surface. Everything was going well (I thought)

I then sanded my last layer of epoxy, washed with acetone and painted on some Evercoat single step gel coat and walked away figuring I was done with that repair. I should point out that the container of Evercoat gel coat says in large letters "DO NOT USE OVER EPOXY." However, there is a white paper on the West System website saying "go right ahead and ignore Evercoat, it works fine." I listened to the advice from West System because I had already bought the gel coat. I came back the next night only to see that my gel coat had gone all drippy and had not cured in most of the repair. Using that same batch of Gel coat I had also touched up one or two other areas. Those areas were fantastic, with a little sanding they were done. Therefore I know it was not a mixing problem. What had happened??

Well my first guess that I had simply blotted on too much and it had prevented proper curing was NOT correct, because my second attempt did the same thing. More internet research led me to a new conclusion: amine blush. Apparently epoxy when it cures can emit a waxy residue that needs to be washed off with soap and water (NOT Acetone, acetone will not remove it), before epoxy can be finished. This is especially true if you are using it has cooler temperatures or if the temperature is dropping during the cure (the exact conditions in my semi-heated garage). My next attempt will be to heat gun the epoxy for a little (hopefully not getting it too hot) to make damn sure it is fully cured, then wash repeatedly with soap and water, then gel coat one last time. If that doesn't work I will start looking into painting options, or maybe I will just grind out all the epoxy and start again, but that does not seem like a good idea and I may just end up with a bunch of new holes in the camper that I need to fix.

The reason I hadn't gone straight to paint was because it seemed easier and cheaper to simply repair a few spots and blend it into the rest of the camper rather than painting over the entire shebang. If anybody has any suggestions for a paint that I can use in a few spots that will blend into the present gel coat that would be great.

Here a few conclusions on gel coat repair that I have come to so far the hard way. First thing, use a Polyester based filler like Bondo to do the repair. Your Scamp is made using a polyester based resin with fiberglass, not epoxy. It is better to keep everything Polyester based, because paints, gelcoat etc. work well with this base. If you are worried about water absorption causing issues in the future (very unlikely, but you never know), use a marine polyester resin instead of the Bondo, but DO NOT use epoxy if you want to gel coat to match the rest of the camper. Even painting over epoxy is not the best idea because even if you sand it with 80 grit sand paper to get good physical adhesion between the paint and epoxy, it will never be as durable because epoxy hates forming new chemical bonds with anything once it has cured. Painting is probably your best choice once you have erred and used epoxy for the repair.
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Old 12-04-2011, 04:37 AM   #2
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Name: Raz
Trailer: Trillium 2010
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Hi Kevin. Although it is at your expense, this kind of post is very useful. Thanks for taking the time. A while back I had to do some interior sealing at the belly band on our Trillium. Everything I read said not to use polyester resin on polyester resin as it would not bond well??? I too went the epoxy resin route. So far so good. At the West Marine store where I bought my supplies a very knowledgeable salesman gave me lots of first hand advice. While I didn't do any gel coat work I recall him saying something about it not drying if exposed to air. To get it to dry he covered it with plastic wrap. As I was working inside the trailer , I really didn't pay that close attention. Might be something to check out. Good luck, Raz

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Old 12-04-2011, 08:56 AM   #3
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Name: kevin
Trailer: 13' Scamp
Posts: 170
Hi Raz,

I know you are trying to be helpful, but I do know how to follow the directions. You are correct that most gel coats require a PVA air inhibitor or to be covered in plastic immediately after application for complete cure. However, the Evercoat single step is not supposed to require it. In fact it seems to cure fine on everything and anything besides my epoxy repair. For instance I pointed out it cured fine elsewhere on the trailer. Icurrently have a patch work of cured, not quite cured, and completely uncured gel coat on different parts of my camper to clean/sand off today. It looks great!!

Oh and if you want some more advice. DO NOT USE 3M 5200 (slow cure) to seal the gap between the upper and lower half of the camper once removing the the belly band if you live in Colorado. Although this stuff is recommended everywhere and even sold at Home Despot, it requires moisture to dry. So it says it will take 48 hours to be tack free and 7 days to fully cure. Well I'm at 5 days to tack free on my way at a snail's pace to full cure. I found some people claiming 2 and 3 week cure times in dry places. I have learned my lesson and next time I will use a fast cure product like 5200 fast cure or the 4200. Neither of which are available anywhere near me and needed to be ordered. This advice applies to all polyurathane sealants/adhesives I think, not really sure, nor do I care. The 4200 I ordered will work. On the plus side the 5200 (slow cure) is sticky as hell and all the marine guys love it for permanent bonding and sealing of through hull applications.
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Old 12-04-2011, 10:01 AM   #4
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Name: Mike
Trailer: 1977 13' Trillium
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Good write-up! I'm a car/house/industrial/commercial painter and have painted all my life. I just learned something....

I have a fiberglass top on my '74 VW camper. I used (3 1/2 years ago) urethane primer and paint. It's still holding up.
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Old 12-04-2011, 12:34 PM   #5
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Trailer: 1979 Trillium 4500
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I'm sorry to hear that you are having grief in your fiberglass repairs. You have described potential problems we may all face. I had extensive repairs to do on our Trillium, including glassing over the joint at the belly band, and I made all the repairs with epoxy and suitable fillers. After the repairs I sanded w/ 150 grit, wiped with wax and grease remover and primed with an epoxy primer and painted with acrylic urethane. Except for some miner orange peel in a spot or two it came out great. I have no experience with gel coat but ,from my experience, you shouldn't have concerns painting over epoxy repairs.
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Old 12-04-2011, 02:04 PM   #6
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Two decades ago I was buying epoxy for flooring and installing it for customers in their blue farm silos (Harvestores). I recall the epoxy people telling a bunch of us dealers at a dealer meeting that epoxies are mostly polyamine or polyamide resins, but they even referred to polyester epoxies. Each type has somewhat different properties and applications. You mention amine blush, so I take it the West resin is a polyamine? Bondo is supposed to be a polyester base, I think. If the different types have problems interfacing with one another sometimes, that's good to know.
To every thing there is a season, and a time to every purpose under the heaven... --Ecclesiastes 3
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Old 12-04-2011, 05:30 PM   #7
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What a bummer.
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Old 12-04-2011, 05:31 PM   #8
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Trailer: 2008 13' Scamp
British Columbia
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I took my boat across Europe from the south of France to Holland through some 300 plus rough concrete locks. I can't even begin to estimate how many gelcoat chips that I've repaired.

As simply put as possible this is the process that I use for non-structural repairs.

1. remove any loose chips and slightly feather the edges

2. cut approx. 3" squares of thick sheet poly, not painting drop cloths. The sheets from old style overhead projectors are excellent but not too available anymore.

3. if the damage is deeper than the gelcoat use some bondo to fill but do not fill higher than the bottom of the existing gelcoat.

4. mix ordinary gelcoat, waxed or unwaxed, doesn't matter.

5. tape the bottom of the poly below the repair and let it hang down

6. use a stick to dap gelcoat into the repair, not too much at first, you can add some as you smooth the poly up the repair.

7. smoothing the poly upwards removes the air and the contact with the poly will leave a glass smooth surface. Hold poly in place with tape on all four edges.

8. With practice you will judge the amount of gelcoat required and it is possible to end up with an almost finished repair.

9. More likely is you will need to use some wet and dry to feather the repair into the existing surface and then buff to a gloss finish.

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Old 12-04-2011, 07:34 PM   #9
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For clarification - is the poly lifted up over the "fix" and then held over it?
I'm real new to this and will be doing some chip(s) repair when the weather is better so trying to get all the info on this as I can.
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Old 12-04-2011, 07:53 PM   #10
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Name: David
Trailer: 16 foot Scamp
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I've used plastic sheeting as described to get a nice smooth and level finish. I actually have several teflon (PTFE) sheets that I use. The teflon will pop free of anything. It can be used over and over.

Here is one source:

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Old 12-04-2011, 11:39 PM   #11
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Name: Ron
Trailer: 2008 13' Scamp
British Columbia
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Yes, the poly ends up taped in place and is left there until the gelcoat sets up.

Since the surface is sealed from air it doesn't matter if you use unwaxed gelcoat.

This process is a mini version of old time "cello finishing" where they used to glass over plywood and wanted a smooth finished surface.

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Old 12-14-2011, 12:38 PM   #12
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Name: kevin
Trailer: 13' Scamp
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Thanks Ron in BC. I used your method for some of the other chips that did not require filler and it seems to have worked great, with much less sanding required.

As a footnote to my previous posts about gel coating over epoxy. My third and final attempt has worked very well. Once the amine blush has been removed with soap and water (acetone no worky) the gel coat cures hard as a rock. The adhesion between the epoxy and gel coat is excellent. I tried to scrape some off and could not for the life of me and ended up sanding it off. A hard earned lesson.
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Old 09-19-2016, 03:47 PM   #13
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Name: Melody
Trailer: Beachcomber
Posts: 25
old thread, but I'm finding it very helpful. Any updating or tips out there?

I started the recent Marine-Tex thread and I may only need to repair brittle cracked gel coat, not the underlying fiberglass. However, the gel coat would need to be molded somewhat as the repair is on a top corner, where there's lots of it.

Marine-Tex is an epoxy? If it just needs some filler in that corner, no fiberglass repair, perhaps Marine-Tex would work best to mold the corner shape....just thought that gel coat wouldn't work overtop of Marine-Tex. Maybe it would if washing it with soap and water after it's set?
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Old 09-19-2016, 04:30 PM   #14
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Name: Steve
Trailer: Scamp 13
Posts: 1,036
Marine tex is an epoxy. You would be better served using Duraglass. It won't soak up water like Bondo which isn't really an issue on a trailer since the repair doesn't sit under water. Duraglass is much harder to finish and adds strength to the repair which Bondo won't do. Its a superior product to Bondo.
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