Fiberglass Crack repair

Discussion in 'Materials' started by muskymania, Sep 29, 2013.

  1. muskymania
    Joined: Nov 2012
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    muskymania Junior Member

    I searched the forum and saw that there were already several other similar threads, however I wanted to post pictures of the crack to give a better idea of what exactly I'm trying to repair. I can't tell how deep it is I just know that it leaks probably around a few gallons an hour. Any advice on how I should go about repairing it would be appreciated.
     

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  2. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    I'm assuming it is a vertical crack. Is there any way you can get leverage and clamps to close the width down? Where is this on the boat? How thick is the fiberglass on each side? How wide is the seperation?
     
  3. muskymania
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    muskymania Junior Member

    I don't think there would be any way to clamp it, its about 5-6 inches long running parallel to one the trailer bunks.
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    This appears to be along one of the lift strakes. Since access from the inside is likely difficult, you'll need to do it from below the boat. Grind back the gelcoat for 3" all around the crack. Next continue grinding the laminate, until it's at least half as thick as it was previously, tapering away from the crack as you go. This will provide a place for the replacement fabrics to live, without standing proud of the surface. Lastly on the prep, grind out the crack, making it bigger, but more importantly clean and well toothed to receive repair materials.

    Now you should have a big gash, where the old one was, the area around it feathered out in a taper to the existing gelcoat, a few inches away.

    Next is the choice of epoxy of polyester. Either will work. The portions of laminate need to be replaced, so you'll need some CSM and some cloth if using polyester or just some cloth if epoxy. Wet out the whole area with whichever resin you choose and apply enough fabric, to fill the depression you've ground into the hull. Stop when you're just shy of the surface, so there's a place for surface fillers, to smooth things out.

    When the first round of reinforcement is glued on, grind it down a bit then apply a filler, so you have something to smooth out. Continue with the surface finishing, until you've go it where you want it, then prep for gelcoat or paint.

    This is the "Cliff's Notes" version. There are lots of previous threads to cover these types of repairs as well as many online videos, books, etc. It's a three step process - first is to grind back to good laminate, removing gelcoat and cleaning out the damage. Second is the application of replacement materials (cloth, CSM, goo, etc.) and lastly is the surface finishing aspects of the job, which has you fair the surface then finish it.
     
  5. muskymania
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    muskymania Junior Member

    Hey PAR thanks for the response. You were correct that its near a lift strake, would you still grind 3 inches even though that will take me over the edge of the lift strake? And also you said generally you sand half way through the laminate layer, any idea about how deep the laminate layer would be on a 16 ft tri-hull?
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You could stop grinding just before you go over the rounded bottom edge of the strake. This will make fairing a lot easier, just working the two surfaces. Since you can only get at one side of the damage (my assumption), you'll need to offer a good bit of reinforcement to the cracked laminate. You can grind down a little, slap on some CSM and hope to get lucky, but usually you just have to come back and do it again (it reappears). As to how thick, well it depends on how it was done, damage location, resin type, etc. The easy way to find out is drill a small hole through the crack and using a hooked wire, get an idea of the laminate thickness. This area will need to be filled anyway, so no real damage from the hole. It could be 3/8" of an inch to quite a bit thicker, so look to remove about a 1/4" of material right at the crack, tapering to near surface level as you move away from the crack. If you had access to both sides (preferred) you wouldn't have to remove as much.
     
  7. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    Most likely Paul's procedure is what is needed. However, if you can get at the inside, an easier repair is possible doing pretty much the same thing on the inside. If working on the inside, you can grind down almost to the gelcoat and do as he said. The easier part is that you don't have to do any finish work on the outside if you only add a few layers of glass at a time to begin with so exotherm doesn't distort the gelcoat.
     

  8. muskymania
    Joined: Nov 2012
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    muskymania Junior Member

    Thanks guys, I ended up going with marine TeX epoxy for the repair.It turns out the laminate was only 1/4 inch thick and I grounded through a small section, hopefully using an injector to get epoxy up inside the hole with the cloth on the outside will give me a solid repair.
     
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