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PostPosted: Tue Aug 24, 2010 8:16 am 
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I know that polyester material is recommended for Hobie repairs by all those in the know. What happens when epoxy is used? I've searched in the forum here, but only seen warnings against using it, not the results. My last (professionally done) bottom job blew out pretty spectacularly last week and I'm getting advice from guys on the beach who swear by a surfers sun curing repair kit. I'm pretty sure that stuff is epoxy. They say they've used it for years with great results.

Thanks.


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PostPosted: Tue Aug 24, 2010 9:17 am 
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I'm not a chemist, but my understanding is that epoxy resin will bond to (cured) polyester with no problems, but polyester resin will not bond properly to epoxy. So what that means is that you can do repairs on your polyester resin based Hobie Cat using epoxy, but if you later do any additional repairs to that same area, you must continue to use epoxy. So, its a much better policy to always use the same resin that the boat is made from - then you don't have to remember and there aren't issues. You also can't get a good bond using gelcoat over epoxy.

As far as your bottom job failing, I would guess it's almost certainly the result of poor surface preparation. The repair area must be properly "roughed up" and cleaned of dirt, dust, and grease prior to laminating.

Sun cure is polyester based, but I would not use it. It cures way too quickly. I would use a proper polyester resin to laminate fiberglass tape.

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PostPosted: Tue Aug 24, 2010 10:13 am 
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From what I've learned on this forum you should use polyester for cosmetic repairs and epoxy for structural repairs/mods. Gel coat does not adhere to epoxy resin very well, if at all. Many people, including me, use epoxy to "glue" the boat together. I'm certainly not the most knowledgeable on this though.

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PostPosted: Tue Aug 24, 2010 8:27 pm 
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Epoxy for bonding, polyester for laminating and where any gelcoat will be applied later. That's a good general rule.

Edit:
Just saw your other post. The UV cure resin is probably polyester, but check it. Does it smell like "fiberglass"? If so, it's polyester. If it doesn't have a strong odor, it's epo. Search for amine blush to find out the problems with epoxy/ gelcoat. Not to mention, it costs a lot more.

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PostPosted: Wed Aug 25, 2010 7:38 am 
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Thanks guys -

Here's a pic

http://flic.kr/p/8viB8D

I think that when the job was done before, they didn't build up the keel. It looks like the surface gel cracked when there was some flexing. Flooded the hull pretty well!

I did fund an interesting page on amine blush http://www.epoxyproducts.com/blush4u.html


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PostPosted: Sun Oct 03, 2010 8:57 am 
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Okay, so then, polyester for delam fix? Is that what I am getting form this? :?:

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PostPosted: Sun Oct 03, 2010 9:51 am 
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I used West System Epoxy on the bottom of my hulls because it is much stronger and will hold up to abuse better. If I was filling in holes topside or something maybe would use poly. Gel Coat is also supposed to stick to the West System Epoxy.


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