Epoxy vs. fiberglass - SailNet Community

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Old 04-16-2010
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Epoxy vs. fiberglass

I've read a lot of the prevoius threads on repairing fiberglass and gelcoat. I don't recall seeing one that mentioned using fiberglass as the repair. Is there a reason not to use fiberglass or is epoxy simply that much better?

Reason I ask is I'm pretty good at fiberglass but have never used the epoxies mentioned. And, quite frankly, there is no place locally that is likely to have them unless Lowes might. I'd have to order everything I believe.

The repairs I'm concerned about are some cracks that go thru the gelcoat into the glass but not very far. Less than 1/4 in. and are on the deck of a Buccaneer, if that information makes any difference.

One other question I have, how hard is the epoxy to sand as compared to fiberglass?

Thanks.

Vic
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Old 04-16-2010
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I don't quite understand your question. I think that you may be looking for the difference in polyester, vinylester and epoxy resins. A quick google search may help.
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Old 04-16-2010
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Vic,

I think you may have misunderstood some of what you read previously.

Fiberglass, or GRP (glass reinforced plastic), or FRP (fiber reinforced plastic) is the term used to describe in generic terms any combination of fiber impregnated with a plastic resin.

What most here are saying is that when making fiberglass repairs, using epoxy resin as the impregnating plastic agent instead of polyester or vinylester resins. Epoxy is superior in terms of bonding strength and resistence to water intrusion.

Take a gander at the West Systems' instructions, which are available on-line here, or download the entire PDF manual here. You can also pick up one of their inexpensive manuals at somelace like West Marine.

Good luck. It's not that hard to do.

Last edited by PorFin; 04-16-2010 at 02:45 PM.
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Old 04-16-2010
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The term fiberglass can be a bit misleading. Generally a fiberglass boat is made using glass fabrics or cloth and a resin that hardens and holds it all together. The resin used can be a vinyl, vinylester or even epoxy based resin. Most boat builders use a vinyl based resin when building their hulls in a mold.
Boats made in this way are said to be made with FRP construction (fiber reinforced plastic) or GRP, if you happen to be in the UK (glass reinforced plastic).
For making repairs to boats like this you could use a vinyl based resin but epoxy resin is generally used as it has superior adhesive and bonding qualities when compared to vinyl resins.
And finally, sanding cured epoxy should be no different then sanding cured vinyl or vinyl-ester resin.
If you have worked with 'fiberglass' before you have probably used a vinyl based resin.
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Old 04-16-2010
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And I thought fiberglass was fiberglass.....but, learning being one of my favorite things to do, I now learn there's more to it than fiberglass, the generic. If I understand correctly, any resin reinforced with glass could be called fiberglass. The things you learn when you aren't even looking to learn about them......

I have previously read a couple sections of the West Marine repair pages for cracks and small holes and those I read only mentioned epoxy. I understand the concept of repair and it is essentially what I've done on snowmobiles and cars and lots of step ladders. I suppose my real question is below......

Ok...from what I understand from the replys, (and thanks to everyone. You added to my knowledge of the stuff my boat is made of), my boat is vinlyester or polyester resin. And from what Caleb said I can use either of these for minor repairs, is that correct? What I won't be getting from the repair is the greater strength and water invasion protection of an epoxy resin, correct? As my use of the boat will not entail any racing or rough weather sailing, will be on a trailer, covered when I'm not actually sailing and will be used a few times a year on small, inland lakes am I sacrificing anything, for all practical puposes, if I use a vinyl or poly based resin instead of epoxy?

Another reason for wanting to use vinyl or poly is because I have a lot of it on hand...but, if it isn't at least suitable for my intended use I'll spring for and learn to use the epoxy.

I never cease to be amazed at the knowledge available here and the willingness of those who know to share that knowledge with those like me who are so ignorant of all things related to sail. Thanks to all of you and to all on the board who so share.

Vic
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Old 04-16-2010
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Quote:
Originally Posted by sharps4590 View Post
A
Ok...from what I understand from the replys, (and thanks to everyone. You added to my knowledge of the stuff my boat is made of), my boat is vinlyester or polyester resin. And from what Caleb said I can use either of these for minor repairs, is that correct? What I won't be getting from the repair is the greater strength and water invasion protection of an epoxy resin, correct? As my use of the boat will not entail any racing or rough weather sailing, will be on a trailer, covered when I'm not actually sailing and will be used a few times a year on small, inland lakes am I sacrificing anything, for all practical puposes, if I use a vinyl or poly based resin instead of epoxy?

Another reason for wanting to use vinyl or poly is because I have a lot of it on hand...but, if it isn't at least suitable for my intended use I'll spring for and learn to use the epoxy.


Vic
The reason you want to use epoxy and not a poly or vinyl based resin is that they will not bond properly and your repair will fail. I wouldn't use what you have on hand for the repair.
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Old 04-16-2010
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Actually I beg to differ, a couple friends of mine used to work for a Fibreglass company that made a lot of the resin that many North American boats are made from. They say that while epoxy is superior there is not that much difference.
I also have some friends that are boat builders and they always use Polyester resin when making repairs. If you are comfortable with resin then go for it.
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Old 04-16-2010
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I believe the difference has to do with secondary bonding. If you build a hull and use polyester and build it all wet it is very strong almost as strong as epoxy. If however you let the glass dry then try to bond another piece to it like a bulkhead or a repair the epoxy has significantly better adhesive properties.
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Old 04-16-2010
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Sharps -
Are you aware that West Marine has no relation to the company that makes WEST Systems Epoxy? The WEST Systems folk have very good books on repairs.
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Old 04-16-2010
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Quote:
Originally Posted by davidpm View Post
I believe the difference has to do with secondary bonding. If you build a hull and use polyester and build it all wet it is very strong almost as strong as epoxy. If however you let the glass dry then try to bond another piece to it like a bulkhead or a repair the epoxy has significantly better adhesive properties.
Exactly !
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