Polyester or Epoxy. Can you tell just by looking? - Fiberglass RV
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Old 09-08-2020, 04:47 PM   #1
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Name: Tim
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Polyester or Epoxy. Can you tell just by looking?

It is so much cheaper to do repairs using polyester....but I canít tell if the original Fiberglass omg is poly or epoxy. The trailer is from 1975...not sure if that helps. Here is a picture of some Fiberglass if people can tell just by looking.
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Old 09-08-2020, 05:03 PM   #2
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1975 will not be epoxy. At that time epoxy woud not be in the open civillian market.
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Old 09-08-2020, 05:59 PM   #3
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Thank you very much
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Old 09-09-2020, 09:36 AM   #4
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I am not going to start an argument. That being said I have used epoxy resin since the early 60,s.. Use epoxy . While it is more expensive it adheres better, is stronger, is waterproof (polyester resin is not waterproof) and most of all the fumes from epoxy are much less toxic than polyester. Overall epoxy will make a better job.
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Old 09-09-2020, 10:33 AM   #5
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I use epoxy for the reasons above, but some people will develop sensitivity or allergy to Epoxies so be aware of that possibility.
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Old 10-17-2020, 10:25 AM   #6
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I've used both and the epoxy systems are easier to use. Epoxy systems will also let you choose between slow, medium and fast setup depending on the catalyst. I will argue that polyester is fine for smaller jobs on a Fiberglass camper if you prep properly and put a top coat over the repair. Also polyester has less shrinkage so it is less likely to pull away from the repair.
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Old 10-19-2020, 09:01 AM   #7
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Name: Dave W
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To use epoxy on what is almost certainly a polyester fibreglass trailer is just silly. To mix polyester and epoxy is just asking for trouble. Sand where you want to add more fibreglass to get through any wax or other residue, then start glassing, with a polyester resin.

For good info, check out this thread: https://www.fiberglassrv.com/forums/...ass-52498.html

Steve Lankford, What are you talking about? Since most, (all?) fibreglass trailers use polyester resin, and the resin is not prone to leaking, I call that waterproof. I do believe you are looking for an argument. If your experience is with constant immersion in water, like a boat, then you are on the wrong fibreglass site. Your advice is inappropriate for the users of this site, and not helpful.
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Old 10-19-2020, 09:03 AM   #8
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I found two gallons of west system marine epoxy and hardner on my buy/sell sight for cheap. So I’ve been using that. I have sanded and ace toned the area before glassing. The stuff is making great adhesion. Thanks to all the advice.
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Old 10-19-2020, 11:23 AM   #9
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It is very unlikely your trailer was made with epoxy, but epoxy is an excellent material to do any repairs with. I've used a lot of it on polyester boats and never had any problems, and as mentioned, you can pick the curing speed and the viscosity with epoxy. That can really help. Epoxy can be as thin as paint thinner, or as thick as peanut butter. It can be made to cure in a couple of minutes, or over a 48 hour time frame.

However, remember that epoxy adheres well to polyester, but polyester does not adhere well to epoxy. So, if you use epoxy, stay with it on all future repairs.
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Old 10-19-2020, 11:27 AM   #10
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Quote:
Originally Posted by Steve Lankford View Post
(polyester resin is not waterproof)

I wonder how many thousands, or millions, of boats have been made with polyester? Are they not waterproof?
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Old 10-19-2020, 12:09 PM   #11
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boats are not water proof they resist water but fill them up with water they sink. submarines are water proof but they are made of steel. almost no one builds with epoxy unless you are rich epoxy with hardener costs 4 times as much as polyester resin but it does have better environmental and health concerns for the people working with it. Osha has pretty much driven polyester resin out of California. and the few places still here using it are very small operations or just patch and repair places. the facility where I work uses 5 different epoxy systems with a net usage of 50,000 lbs a year. its strengths are good but its weaknesses in using it with cured polyester are problems not easily overcome. its not a perfect solution for everyone especially if your planning to over coat your repair with polyester gellcoat.
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Old 10-19-2020, 12:31 PM   #12
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Quote:
Originally Posted by stevebaz View Post
boats are not water proof they resist water but fill them up with water they sink. submarines are water proof but they are made of steel.

I'm afraid I don't understand this: Fill a boat with water and it sinks, means it is not waterproof, or that the resin dissolves? Submarines are waterproof? Does that mean they can't sink, or that steel doesn't rust?

I'm puzzled.
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Old 10-19-2020, 02:13 PM   #13
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Water will migrate through polyester, but slowly. That is enough to let the wooden stringers in boats rot out and is very common.
Here is a link to the breakdown of polyester fiberglass in the presence of water.
Ideally there would be no issue in a FRG trailer, but if there is a leak and the water stands it will migrate through the fiberglass and attack the wood. One answer is no leaks, the other is seal the whole floor with epoxy glass and spend the extra money.
I got a good price on the epoxy I used so I did all of my repairs with it.

The Real Story of Osmosis Blistering
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Old 10-19-2020, 06:07 PM   #14
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Originally Posted by redbarron55 View Post
Water will migrate through polyester, but slowly. That is enough to let the wooden stringers in boats rot out and is very common.
Here is a link to the breakdown of polyester fiberglass in the presence of water.
Ideally there would be no issue in a FRG trailer, but if there is a leak and the water stands it will migrate through the fiberglass and attack the wood. One answer is no leaks, the other is seal the whole floor with epoxy glass and spend the extra money.
I got a good price on the epoxy I used so I did all of my repairs with it.

The Real Story of Osmosis Blistering
Gelcoat is a lot harder to get to adhere to epoxy than Polyester. These trailers are made using polyester,so why would you think epoxy is needed or "Better"?
The amine blush residue needs to be removed from epoxy prior to any sanding or recoating.
polyester can be thickened just as well as epoxy can...up to peanut butter consistency,think hull and deck putty.
I have used tons of epoxy and wouldn't use it on these trailers,not needed and more expensive.

Perhaps the fanatics in the republik of Kalifornia are doing great work in restoring the environment....Just as banning plastic straws has made a world of difference.......
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Old 10-19-2020, 06:22 PM   #15
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Originally Posted by stevebaz View Post
1975 will not be epoxy. At that time epoxy woud not be in the open civillian market.
Sounds about right.
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Old 10-20-2020, 07:54 AM   #16
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I don't know about anyone else's Scamp, but I don't have gelcoat inside where the floor id bonded to the shell and the floor is not gel coated either.
I mean to indicate that the floor is the point of failure due to rot from leaks, not the shell.
For repairs to the shell polyester would be fine, but for me and the floor where water may go undetected for a while I would and did use epoxy and fiberglass cloth to seal the floor, top, bottom and sides.
So far I have not seen the fiberglass shell rot out, but I have seen many floors rotted from water collecting on the inside and not detected.
Well they may have been detected, covered and sold down the river as I think about it now.
Investing so much time and labor into the repairs a little more for the epoxy resin is a small expense with a fairly big return (at least for whoever has this trailer after we pass away). I won't have to fix the floor again, of that I am sure.
As to gelcoat adhesion I painted my trailer with epoxy primer (sticks to anything) and polyurethane top coat.
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