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Thread: Sealing leaking fiberglass fuel tank

  1. #11

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    Nov 2011
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    Thanks to everyone for your input and suggestions. I have now have better plan to go about repairing my leak.
    T Madison

  2. #12

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    Sep 2011
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    When I bought a fiberglass homebuilt awhile back it had tank leaks. I tried sloshing something (red) from PolyFiber that a friend gave me and that was a large mistake. Never cured well, etc. I have no experience with the compounds that are mentioned in this thread and they may work well (fuel & alcohol resistant, adhesion, curing well), but I wound up having to remove my tank, cut it open, sand the surfaces, and coat with PolyEsther Resin. It's impervious to ethanol, bonds with epoxy resin. I have had no leaks in the 3 yrs since and am flying with mogas (Chevron). A big pointer that is mentioned in the thread is that the pinhole you find on the outside is not neccessarily where the inside hole begins. The vacuum method is not going to suck compound all the way along that path.

  3. #13
    Anymouse's Avatar
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    Quote Originally Posted by flyrgreen View Post
    The vacuum method is not going to suck compound all the way along that path.
    It doesn't need to. It just needs to do it enough to plug the leak. Pin hole leaks aren't very big and normally don't take much resin to seal.
    Someday I'll come up with something profound to put here.

  4. #14

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    Sep 2011
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    Polyesters are low viscosity, cheap and are not as fuel resistant as epoxies. Many tanks for kitplanes are made from it because of cost and you can identify polyesters by sanding a tiny corner and smelling for styrene. Epoxies would have no styrene odor.
    The novolac (epoxy/phenolic) is lower viscosity and more fuel resistant, so it would be a better choice. If your tank is sealed and working, just keep the material choices in mind for next resealing.

  5. #15

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    Sep 2011
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    In my previous reply I mis-identified the compound I used to repair my fiberglass tank. I in fact used Vinyl Ester Resin, from reading in one of the EAA publications, that recommended Vinyl Ester for it's resistance to ethanol (and alcohol in general). I'm hoping to hear from some of you that this was the right move. -rg-

  6. #16

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    Sep 2011
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    If you used a vinyl ester resin to repair a structural issue in tank and left it bare, it will eventually breakdown in ethanol mogas over several years. It also depends on the concentration of the ethanol. In Calif, it's 10% ethanol. If you used the vinyl ester and coated it with novolac to keep ethanol from contacting the ester, tank will last much longer. So it depends on how ester was appiied and it's exposure. If you can still coat tank interior, no matter what the structural resin system, it wold be beneficial to avoid breakdown over time.

    If you put a tank into service and monitor the fuel filter, gradual breakdown will produce a fine sludge and then small bits of glass fibers. By the time fibers are showing, the breakdown is progressing. Coating at that point may keep damage from accelerating and save tank. I feel it's better to coat first and avoid any breakdown.

    Often on threads like this, people come from different situations so it's hard to give an overall answer to every question. Some will swear that bare structure of any resin will withstand mogas exposure, only to find that their mogas has no ethanol or a very low concentration so they really have no dissolution issues. Others with high concentrations will eventually have a problem. My recommendations are based on a high ethanol (10%) continuous exposure.

  7. #17

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    Re the last post: This is simply not true... Vinylester IS impervious to fuel and needs noadditional coating. How do I know this? I own a Glasair III that is constructed using Vinylester resin (yes, even the fuel tanks) and there is no need to coat the tanks with anything. Hundreds of Glasairs have been flying for the last 25+ years without a problem.

  8. #18

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    The problem concerned mogas with ethanol. If you are using avgas without ethanol, no problem, as almost all of the tank resin systems will work. But if you are using mogas, there will be gradual degradation without a coating.

  9. #19

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    Oct 2018
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    Franklinton, Louisiana
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    Do Not Use Sloshing compound of any type.

    Quote Originally Posted by Brian E. Evans View Post
    You can buy sloshing compounds from the usual suspects. they do take several days to dry, and are ideal if you cannot locate the source of the leak.
    If you know where the leak is, then it would be quicker to cut the fabric, do a fiberglass cloth and polyester ( or epoxy.) resin repair. Double check for more leaks then repair and repaint the fabric.
    Brian Evans.

    A P-51 Test pilot with over 13,000 hours died in Florida on his second flight in a Stewart P-51 and this was due to the lack of integrity of all sloshing compound sealants. I do not recommend ANYONE using this product for ANY application whatsoever. It will desegregate and clog causing fuel starvation.

    Sincerely and Respectfully,

    Yellowhammer

  10. #20

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    Feb 2019
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    Quote Originally Posted by Yellowhammer View Post
    A P-51 Test pilot with over 13,000 hours died in Florida on his second flight in a Stewart P-51 and this was due to the lack of integrity of all sloshing compound sealants. I do not recommend ANYONE using this product for ANY application whatsoever. It will desegregate and clog causing fuel starvation.

    Sincerely and Respectfully,

    Yellowhammer
    Can you provide some specifics on the cause of that fatal crash?

    Thanks,


    BJC

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