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Thread: Repairing cracked epoxy on bottom of hull

  1. #1
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    Default Repairing cracked epoxy on bottom of hull

    After running over quite a few rocks, the bottom of my hull which is a few layers of graphite mixed epoxy, the epoxy has some gouges down to the fiberglass which I plan on repairing with some thickened epoxy but there are several ares where the epoxy has cracked.

    Should I use a paint scraper to scrape away the loose cracks or sand them down or both?

    I'm going to try the Wetlander product and they said using over epoxy is fine as long as the epoxy is in good condition and sanded down with 150 grit.

    Thanks in advance.

  2. #2
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    Default Re: Repairing cracked epoxy on bottom of hull

    We could use a bit more info here. What exactly is the hull made of? When you say that the epoxy is cracked, how thick is it and are these cracks down into the fiberglass or in some sort of unreinforced layers on top of the glass? While being lower friction, one of the problems with graphite/epoxy mixtures is that they are noticeably softer than plain epoxy is. This is one reason why it isn't uncommon for them to be prescribed in a mixture of only around 10% by volume. Loading the mixture up with substantially more graphite can make a very nice-looking substance, but it is also much less resistant to abrasion and weaker than plain resin. If they are just cracks in the coating and the glass under them is still OK, I'd probably repair them the way we would repair cracks in fiberglass gelcoat. You take a small "V"-shaped grinder bit (Dremel-sized) and follow the crack, widening it at the surface into a V-shaped trench. Then that gets filled, is allowed to harden and is finally sanded and polished to match the original surface. Anything that requires a lot of sanding on a graphite/epoxy surface tends to make an unbelievable mess, so excessive sanding is to be avoided.

  3. #3
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    Default Re: Repairing cracked epoxy on bottom of hull

    Can you share a pic of what a crack means? Does it go through to the wood?

  4. #4
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    Default Re: Repairing cracked epoxy on bottom of hull

    Some of them were deep enough to get down to glass which I plan on fixing with some thickened epoxy and others on on the top film which I think would go away when I sand it down with 150 grit before putting on wetlander.

    20221204_155935.jpg20221204_163727.jpg

  5. #5
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    Default Re: Repairing cracked epoxy on bottom of hull

    A couple thoughts:

    The damage to the bottom coating would have been much easier to repair it the FG had been simply painted, without the thick layer of graphite/epoxy. Epoxy/FG is pretty darn abrasion resistant and really doesn't need an additional thick layer of epoxy to protect it.

    If you anticipate this type of damage might occur in the future, you should consider adding sacrificial strips of a decent hardwood that can be easily replaced when damaged.

  6. #6
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    Default Re: Repairing cracked epoxy on bottom of hull

    From the looks of the edges of what came away I'd be very suspicious of what kind of bond there is between the fiberglass and the graphite-bearing layer on top.

    Depending on just how pervasive this kind of damage is on your hull and how long you expect to keep using it, you may be best advised to start sanding as much as you can off down to the 'glass and starting over.

    If you can scrape anything off, anything you put on over it isn't going to last. Proper epoxy bond won't ever be scraped off.

  7. #7
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    Default Re: Repairing cracked epoxy on bottom of hull

    Fix it like you posted...scrape, sand, clean, apply new coating...with cloth if the cloth is fractured.

    What type of boat is this?

  8. #8
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    Default Re: Repairing cracked epoxy on bottom of hull

    It's a drift boat that I use on rivers so it gets scraped up a lot.

    Last winter was the first winter for me to do repairs after a season of use.

    Instead of fixing only the spots where the epoxy scraped down to the glass, I had roughed up the entire bottom and applied two think coats of epoxy/graphite mix.
    After doing that, I had realized I should have just did the spot touchups.

    I want to get it to a good point to be able to put down the Wetlander product.

    I hope I don't have to sand it all the way down to the glass.
    I did see an youtube video by Ross Lillistone where he used a scraper and heat gun to scrape away cured epoxy which looks easier and less of mess than sanding.

  9. #9
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    Default Re: Repairing cracked epoxy on bottom of hull

    In this instance a heat gun is a Good Idea. Maybe some heat-resistant gloves as well.

    Cured epoxy over 160F ought to become soft enough to yield to being scraped off fairly easily. What surprises me is how clean the exposed 'glass/epoxy material is where the graphite-augmented stuff got knocked off. With a proper bond I'd expect to see some evidence of black stuff remaining behind, not what looks like pretty clean, undamaged (save for the evident abrasion) 'glass left exposed.

    As Todd's related, sanding graphite-bearing epoxy's about as nasty an undertaking as I'd ever imagine having to tackle. I'd certainly try the heat gun + scraper first before getting out a sander & donning proper PPE.

  10. #10
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    Default Re: Repairing cracked epoxy on bottom of hull

    Thank you all for the replies.

    A heat gun and scraper are wonders, just tried it, glad to know about this rather than have to sand like crazy.

    There are only a few patches I need to repair so I'm may just touch those up with epoxy and give it a go another couple of seasons rather than take it all off and replace it.

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