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Old 10-08-2012, 21:46   #1
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Stress Crack Repair

I have a number of stress cracks to repair on an old boat. I know the usual procedure using gelcoat paste, but I am more interested in strength and durability than in appearance. Besides, the cracks are in the nonskid area, so it is not going to look like new. I just want a strong bond that will keep water out. Are there some products that are stronger than gelcoat paste but not absolutely ugly? Perhaps an epoxy product, such as G/flex (with white coloring)?
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Old 10-08-2012, 22:21   #2
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Re: Stress crack repair

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Originally Posted by Mike Sibley View Post
I have a number of stress cracks to repair on an old boat. I know the usual procedure using gelcoat paste, but I am more interested in strength and durability than in appearance. Besides, the cracks are in the nonskid area, so it is not going to look like new. I just want a strong bond that will keep water out. Are there some products that are stronger than gelcoat paste but not absolutely ugly? Perhaps an epoxy product, such as G/flex (with white coloring)?

The only thing which will keep stress fractures from returning guaranteed forever is to grind and glass them. If you have a bunch on your decks, which is quite common, you can grind and glass them all and fair them out, then sand the existing skid pattern off and paint the whole deck with new skid. Anything else and the cracks will eventually reappear. Stress fractures often lead to wet core.
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Old 10-08-2012, 22:49   #3
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Re: Stress crack repair

I 2nd minaret's recommendation and add that doing any and all preventative maintenance ahead of time (like dealing with the stress fractures now as opposed to putting it off til next season...) is always a lot less work in the end (especially if your core materials are potentially subject to rot..).
In working on my boat I've had to do A LOT of grinding and glassing and depending on your set up it can be horrible dusty work or not that bad at all so I would would highly recommend using dust collection on an angle grinder (personally I use the "dustbuddie" and I no commercial affiliation with them) with a router speed controller and metal flapper disks. The router speed allows you to slow down the angle grinder when you want to improve the effectiveness of the dust collection and metal flapper disks (grit dependent on how aggressively you need to remove material but initially 120 is probably good given that you can remove a lot of material pretty fast) and since they are designed to grind metal so they last a really long time...
Good luck,
Dave
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Old 10-08-2012, 23:08   #4
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Re: Stress crack repair

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I 2nd minaret's recommendation and add that doing any and all preventative maintenance ahead of time (like dealing with the stress fractures now as opposed to putting it off til next season...) is always a lot less work in the end (especially if your core materials are potentially subject to rot..).
In working on my boat I've had to do A LOT of grinding and glassing and depending on your set up it can be horrible dusty work or not that bad at all so I would would highly recommend using dust collection on an angle grinder (personally I use the "dustbuddie" and I no commercial affiliation with them) with a router speed controller and metal flapper disks. The router speed allows you to slow down the angle grinder when you want to improve the effectiveness of the dust collection and metal flapper disks (grit dependent on how aggressively you need to remove material but initially 120 is probably good given that you can remove a lot of material pretty fast) and since they are designed to grind metal so they last a really long time...
Good luck,
Dave
Too slow for me. I use a variable speed Milwaukee mini-grinder with 16 grit discs and no shroud (which lets you get much closer to corners and edges and have much better control), I just have a single huge grind session with lots of tenting and masking beforehand and lots of vac attack afterword. Then glass everything a little high and grind again close to fair. Then instead of bondo for fairing I am already close enough to just brush on 3-4 coats of gel coat and block it out fair. This gives you a bomber glass repair with no bondo or other fairing compound, just glass and gelcoat as it was when it came from the factory. With practice and planning it is also faster than working in bondo. When finished it is ready for either paint or new gel, and the surface will already be pinhole free for a nice shoot. I don't like flapper wheels because you can't grind fair with them. Sometimes I even use a 7" grinder instead of a 5" on small repairs, because it will grind fairer faster, even though it's harder work. The 7" has more flat surface area. The flapper has none.
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Old 10-08-2012, 23:50   #5
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Re: Stress crack repair

Sounds like you've got an entirely different but equally functional system already. :-) I've got an epoxy boat and so I mix fillers (wholesale mixed epoxy + appropriate mix of mill fibers, silica, chopped fibers, dicaperl, etc) appropriate for the task at hand as I need them so I haven't used bondo since land-based projects, and in the case of an epoxy boat mixing my own fillers lets me avoid the very expensive fairing compounds on the the market, and then if I fair with a fairing board while the epoxy is still somewhat green it's incredibly quick and easy..
Dave
P.S. Admittedly for the truly small projects and/or spaces I always go to my Milwaukee M12 multitool and related accessories gets into the spaces an angle grinder or 6" sander can't get into.. :-)
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Old 11-08-2012, 09:35   #6
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Re: Stress crack repair

To be clear, in our boatyard "bondo" is a derogatory term for any fairing compound whatsoever, epoxy included.
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Old 11-08-2012, 09:41   #7
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Re: Stress crack repair

Mike, a pic is worth a thousand words. You dont say if these are just hairline gel cracks or gaping ones, or in between. Personally, I doubt hairline gel fractures are an issue. Boats flex, reinforced glass/resin flexes pretty forgivingly. Gelcoat on the other hand is not reinforced and brittle, so over time it may show hairline cracks.......
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Old 11-08-2012, 09:43   #8
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Re: Stress crack repair

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To be clear, in our boatyard "bondo" is a derogatory term for any fairing compound whatsoever, epoxy included.
and yet.... high build primer seems like a much softer, more powdery product than Bondo.... yet yards love to use it.....
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Old 11-08-2012, 09:46   #9
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Re: Stress crack repair

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Mike, a pic is worth a thousand words. You dont say if these are just hairline gel cracks or gaping ones, or in between. Personally, I doubt hairline gel fractures are an issue. Boats flex, reinforced glass/resin flexes pretty forgivingly. Gelcoat on the other hand is not reinforced and brittle, so over time it may show hairline cracks.......

I would say about 90 percent of the stress fractures I grind out go well into the glass. Probably half go right through. I can't count the clients who have told me "the broker said the cracks were only cosmetic and don't go into the glass". Probably about 30 percent of the wet core I replace is caused by stress fractures instead of poor or failed bedding.
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Old 11-08-2012, 09:51   #10
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Re: Stress crack repair

Stress cracks in gelcoat will keep coming back if the area under the gelcoat keeps flexing. The area under the gelcoat will need to be reinforced to stop the flexing....if it is a practical thing to do.

Otherwise you may consider paint, which is more flexible than gelcoat.
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