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Old 08-03-2009, 13:55   #16
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I never indicated that the plan was to gelcoat over bare plywood. I was hoping that somewhere from the forum I was going to get some information from a professional that had some real world experince with the exact application I have described. While most professionals would never think of coating over epoxy with a poly or vinylester based gelcoat it is true that epoxy forms a better bond with wood. That issue is made up for by priming the plywood with an acetone thined polyester resin that will be rolled or sprayed on the plywood, when that is tack hard followup coats of polyester will be applied to achieve a base to spray muliple coats of gelcoat to 20mls thick. An issue of importance here is to achieve a chemical bond between all the layers, that will never be achieved between epoxy and gelcoat. 90% of all fibergalss boats are made from fiberglass and polyester resins and should always be repaired with products of the same chemical composition. Don't take my word for this see LBI's website
@ www.lbifiberglass.com, they have been in the businees of supplying both epoxy, polyester and vinylester resins to the boat building and manufacturing industry for over 30years and speak very clearly about waht should go with what. Regarding Awlgripping vs gelcoat, gelcoat is signifigantly tougher than paint as well as easily repairable, just buff a scrtach out, try that with Awlgrip.
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Old 08-03-2009, 14:30   #17
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Capt Cook, kinda what I was leaning towards. FYI for the rest of group epoxy and gelcoat are not compatable with each other
Are you Rip Van Winkle? Articles written in the last several years directly contradict this statement. You've already been pointed to one such article. I suggest you read it before telling all of us how wrong we are.

As to your project. You can do it the cheap way, or the right way. It's your reputation, not ours.

Use the cloth.
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Old 08-03-2009, 14:34   #18
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I mentioned Awlgrip (or any 2-part LPU) in relation to using epoxy instead of polyester. I think Awlgrip over epoxy would do better than gelcoat over epoxy.

cheers,
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Old 08-03-2009, 14:52   #19
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... 90% of all fibergalss boats are made from fiberglass and polyester resins and should always be repaired with products of the same chemical composition. Don't take my word for this see LBI's website
@ www.lbifiberglass.com.
This caught my eye and in looking through their site, I couldn't find where they mentioned it. I saw they recommended not mixing resins of different compositions when doing repairs, but never could find where they recommended staying with materials of the same chemical composition when doing repairs. In fact I thought their suggestion on reinforcers, etc. suggested otherwise. I also felt their discussion of epoxy suggested it was a good material for many applications and I wonder why they'd say that if they feel it's incompatible with most every boat ever built.

Can you please point out the section where they discuss repairs only being made with the same products as the original construction? I'd like to read more about their thinking on that, especially since Epoxyworks in the link Christian provided starts out by saying how wonderful epoxy is as a repair material, which has also reflects my experience with it.
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Old 08-03-2009, 14:55   #20
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I prefer to always follow the manufacturers reccomendations. As the boat is already coated with vinylester epoxy is not an option. Regradless of epoxy vs vinyl the question was regarding wether a cloth was required to do this project not what coating to use.
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Old 08-03-2009, 17:26   #21
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- Consider awlgrip instead of gelcoat for reason above. Or consider use of polyester instead of epoxy.
Awlgrip awlgrip awlgrip

BAH, is it really any better than other brands?
It is certainly a whole lot more expensive.

Or are you just saying Awlgrip as an all encompassing meaning for two pack paint like many people seem to call boats built in epoxy as the "West System" even though west resin isnt allowed within 1000 metres of the build.


I do agree in the idea of using a good quality urethane or poly urethane over epoxy primer over epoxy and light glass for the ply, but don't agree that awlgrip is the be all and end all having seen plenty of examples of under performance for the $$$ spend over the years

Quote:
My pref would be epoxy + awlgrip but it is the more expensive one.
So don't use awlgrip,

Use Ameron, Jotun or another brand, preferably with pictures of mining and industrial equipment on it instead of boats.

gets down off soapbox


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Old 08-03-2009, 17:32   #22
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I mentioned Awlgrip (or any 2-part LPU) in relation to using epoxy instead of polyester. I think Awlgrip over epoxy would do better than gelcoat over epoxy.

cheers,
Nick.
Ahh, just saw this comment

Still not a fan of LPU, urethanes , in my experience are very easy to blend repair and buff back in compared to other breeds that can require a repaint

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Old 08-03-2009, 17:50   #23
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A lot of VERY bright people believe that, NO MATTER WHAT resin your boat is built with, EPOXY is THE choice for repair and any type of bonding. Boats are repaired every day with epoxy, and when the repair is complete, gelcoat is sprayed on...I would never use any other type of resin. You are looking for a professional opinion? Funny, I just saw a "professional" at my marina use auto body putty and polyester resin for a repair...
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Old 08-03-2009, 18:04   #24
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Of course they are. Gelcoat adheres to epoxy just as well as it adheres to polyester.
Only as a secondary (mechanical) bond. Not as a primary (chemical) bond.
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Old 08-03-2009, 18:04   #25
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How did I know that this would turn into a @#$$ing contest...I did my best to answer the question at hand. I would not recommend thinning with acetone as some funky things can happen...use styrene. If I were glassing in tabbing or say installing a shelf I would use epoxy and no you don't thin epoxy, yes it is stonger and perhaps a better bond. I use Awlgrip all the time, I know what to expect with it. I still like gelcoat for many projects for speed/repairability. I always give customers a choice of materials and explain the differences. Epoxy/LPU will at least triple the material and labor costs, turning a $700 job into $2000 or more...I think the gelcoat will yield a respectable result at a reasonable price. I doubt the customer wants a $2000 finish in his shower.
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Old 08-03-2009, 18:34   #26
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A lot of VERY bright people believe that, NO MATTER WHAT resin your boat is built with, EPOXY is THE choice for repair and any type of bonding. Boats are repaired every day with epoxy, and when the repair is complete, gelcoat is sprayed on...I would never use any other type of resin.
Totally agree


Quote:
You are looking for a professional opinion? Funny, I just saw a "professional" at my marina use auto body putty and polyester resin for a repair...
I have seen some stuff holes with newspaper and then top up with bog (putty)

It was a good newspaper though

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Old 08-03-2009, 18:35   #27
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Epoxy/LPU will at least triple the material and labor costs, turning a $700 job into $2000 or more...I think the gelcoat will yield a respectable result at a reasonable price. I doubt the customer wants a $2000 finish in his shower.
Can you enlighten us as to how you figured out these calculations?

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Old 08-03-2009, 19:03   #28
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Captjcook,

"pissing contest"???-- the tone was set in post #3 !!!
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Old 08-03-2009, 19:07   #29
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Is the hull smooth enough, simple enough, so that instead of doing glass work you could bond a sheet of formica or similar material to it instead? Cheaper, faster, equally durable and probably a way smoother more professional finish. (I'd bond it with an expanding urethane glue for a permanent and void-free bond.)

Doing a smooth job with FRP, and then spraying with gelcoat (air-curable, or coating the real thing) has got to be a way more expensive way to go.
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Old 09-03-2009, 06:31   #30
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The reason for not using epoxy for repairs on polyester hulls (hulls, decks) is that it would create hard spots. I think it also depends on how big the repair is.

I'm lucky enough that I never needed a hull repair so I don't have any experience with this theory but hear and read it often so guess it's "general knowledge".

cheers,
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