Fiberglass repair the right way? - Page 3 - SailNet Community
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post #21 of 32 Old 11-11-2007
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and ( just to make people think im even more simple), you should 90% of the time work from the outside of your hull in,, most boats are made with the heaviest glass on the inside, and compromising that the least is the strongest way,and safest patch.

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post #22 of 32 Old 11-11-2007
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LOL... actually, physics also supports that idea... the water pressure would help hold an external patch in place, but would be working against an internally place patch, since the water would be pressing itw away from the repaired surface, not into the repaired surface.

BTW, I don't see where the OP (davidpm) ever said how large the patched area in question was... if you did, please quote it for me... since you said that the patch in question was significantly larger.
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and ( just to make people think im even more simple), you should 90% of the time work from the outside of your hull in,, most boats are made with the heaviest glass on the inside, and compromising that the least is the strongest way,and safest patch.

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post #23 of 32 Old 11-11-2007
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what haffiman is saying is, that rock hard epoxy doesnt flex the same as the poly,,,there lies ya problem and where ya cracks are going to be. so to keep that from happening you need to use what everything around the patch, is made from poly,,,,, and the mechanical bond is bout the same for poly as epoxy,,, its just that the epoxy is harder,,it doesnt mean it "sticks" any better
The mechanical bonding/adhesive properties of polyester isn't even in the same ballpark as epoxy, and if your expierience has shown polyester to be as strong in an adhesive role as epoxy, I'll submit that you epoxy was either not mixed correctly or the surface was not prepared very well.

For normal repairs, I have seen the high shrinkage of a polyester repair cause many more "cracking" probelms than any flexing issues with epoxy. I agree that epoxy is harder, but I would also suspect that you would have more issues with stiffness or flexing due to the fact that the typical repair is made of a differant layup material than the original hull, ie a patch made with biaxial glass will be more rigid than a chopper gun hull, regardless of the resin used.
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post #24 of 32 Old 11-12-2007
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Working from Inside
If the damage area is small and above the waterline, make the repair from inside the hull, if possible. You are going to bevel the edge of the hole with a 12-to-1 chamfer, so if you repair a 3-inch diameter hole through a 1/2-inch-thick hull from the outside, you end up with about 15 inches (diameter) of surface damage to refinish. Repair it from the inside and you have only a 3-inch hole to refinish.<<< 15 inch hole , quoted from the casey page,,, and nowhere did i say that poly adheres stronger then epoxy i said the mechanical bond is bout same hehe ( how deep into the poly does epoxy melt into, and if it does that isnt it a chemical bond?),, just because something is stronger or does something better doesnt mean its ALWAYS the right answer,,and if your any kind of fiberglasser you know there is shrinkage and you deal with that and it ends up right,,,,,,take a 3 foot square of glass,,lay it up with poly,,, cut a hole bout say,,5 inches,,repair it with epoxy,, now take it and bend it,,,,,what flies?,, that epoxy patch does,,,,now do the same with epoxy and glass,,,fix the hole with epoxy,, bend,,, what flies??? nothing.

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Last edited by the1much; 11-12-2007 at 08:59 AM.
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post #25 of 32 Old 11-12-2007
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and i fergots bout the way the epoxy was mixed,,, all 3 guys have been doing glass work for over 30 years each,, they tried telling the owner not to use epoxy,, but he got it in his head that it was stronger so it had to be better,, and i cant imagine they did ALL 8 port lights in 1 batch of resin,, and i cant imagine they could mix it wrong all 8 times. and i know them slow old dudes didnt do it on same day.

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While it may not have been mixed incorrectly each time, the person, if unfamiliar with epoxy work, may have used the wrong type of hardener or done something else, like mix epoxy in the wrong type of container, and contaminated the epoxy each time. In one case, down at my marina, a guy was using waxed paper cups to mix epoxy... with somewhat unpredictable results.
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and i fergots bout the way the epoxy was mixed,,, all 3 guys have been doing glass work for over 30 years each,, they tried telling the owner not to use epoxy,, but he got it in his head that it was stronger so it had to be better,, and i cant imagine they did ALL 8 port lights in 1 batch of resin,, and i cant imagine they could mix it wrong all 8 times. and i know them slow old dudes didnt do it on same day.

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post #27 of 32 Old 11-12-2007
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i cant say what they did,, i wasnt helping, but i do know they knew a very lot bout epoxy, and worked with it for years. as of me i've used epoxy maybe enough times all together to stick 10 boards together ( short boards) , and it was them same oldies that told me how to repair it and why it happened, then handed me a 9 inch wildcat and said cut-em out.lol the perks of seniority
so when it comes to epoxy im a idiot,,and will be learning forever,, but i do know what i've had to deal with and how the "teachers" taught me to do it so i didnt have to do it again lol

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post #28 of 32 Old 11-15-2007 Thread Starter
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So what is the bottom line here?
There seems to be two basic disagreements.
1. If you have a 4" hole in a 1/4" thick hull tapered out to a 10" depression do you put in a 5" piece first (1/2" overlap) or do you put the the 10" piece first and let it belly to the bottom of the hole?
2. Are you better off using epoxy for extra strength or poly to match hardness and shrinkage of hull?

If I got the questions right I may be able to find someone with an engineering answer.
It looks like any combination will work as we have two experienced people with different takes. The bottom line may be that it dosn't matter much. Or there may be certain conditions that favor one approach over another. I just want to make sure I have the question right before I take it to the engineers.
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post #29 of 32 Old 11-15-2007
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The lager piece goes in first.

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post #30 of 32 Old 11-15-2007
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we usually go small first, that way your largest piece is usually just mat, there basically for the fairing,,thats why we go from small to big, and because if you start from inside where the strongest glass is, you only take out a little of what matters, leaving the cosmetic (largest) outside piece last. this i think gonna turn into the " chicken or the egg" threads haha
as for #2 heh,,you got opinion

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