Acceptable method of extending the life of wood in GRP

Discussion in 'Boatbuilding' started by Magnus W, May 5, 2019.

  1. Magnus W
    Joined: Nov 2017
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    Magnus W Senior Member

    With increasing age there comes a time when the cost of labor and materials for doing a "proper" repair on a boat becomes to great.
    In addition to the cost perspective, one can argue that doing it properly might be over the top for other reasons too. If the boat on a 0-10 scale (with 0 being scrap, 1 is barely working and 10 being mint) is an overall 3 a proper repair of a component, thereby lifting to 10, can be overkill as the boat in general will be just as rough regardless.

    I've fixed up a few windows and garden furniture by diluting epoxi with methanol and applying it on the affected wood (early to moderate stages of rot). It takes very little methanol to make the epoxi watery and the dry wood really literally sucks it up.
    The oldest window is now on the tenth year since the "repair" and it's just as good (or bad) as it was when I treated it.

    I was worried that the the transition between treated wood and untreated wood would be a weak spot, or that the treated wood/rot, would be brittle but as far as windows and furniture goes that doesn't seem to be the case. But a window is not a boat.

    I'm wondering if the same method can be used on boats, like for fixing a soft spot in a transom or a rotten stringer?
    Opening up a small part of say a transom and letting the damaged wood dry before epoxi treatment and then sealing it up would be much smaller affair than cutting it up completely. Perhaps "good enough" and certainly better than doing nothing.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Bodgie jobs always have to be seen in the context of safety, if it compromises safety, and some other steps are not taken to compensate ( like installation of buoyancy foam), then it is flirting with danger.
     
  3. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    Some good info here: Thinning WEST SYSTEM Epoxy https://www.epoxyworks.com/index.php/thinning-west-system-epoxy/

    So if the wood fibers are damaged epoxy won't make it as strong, only hard. And diluted epoxy won't have the strength or moisture resistance.

    The guy from Sail Life who is fixing up a sailboat is planning to coat rotten stringers with 3mm fiberglass. The fiberglass will basically take over the structural load for the stringers. Kind of crazy but apparently he talked with an engineer.

    PS: I should add I have zero experience, just curious about this as well.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    That makes more sense than painting rotten timber with "magic" restoratives. A bonding coat of resin rich mat can be followed by unidirectional glass, without adding too much weight, but of course the boat won't be like new, and will have gained unwanted weight.
     
  5. Dejay
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    Dejay Senior Newbie

    Yeah, in his case the weight is down at the bottom and only like a hundred kg.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    You are basically using the old framing as a former for your glass, I think it is viable, at least in some situations. The idea of rotten wood festering away seems to be a deterrent for many, but obviously strength requirements have to be met, and transom repairs are not approachable in quite the same way.
     
  7. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    Several decades ago the idea of thinning epoxy seemed like a good idea, too bad the chemistry didn’t follow the the same line of thought.

    Covering the existing stringer with more glass works well, but.....

    You need to make sure the old stringer is still attached securely to the hull, the workmanship on of some these old boats is so bad that the reason for the rotten wood is the miserable attempt they made at glassing them in place. Often times the old laminate is barely attached to the hull.
     
    Last edited: May 5, 2019
  8. Rumars
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    Rumars Senior Member

    There is no method to repair structural wood without replacing it. You can do that with wood or you can use other materials. In the example above the woods strenght is replaced with fiberglass. Leaving the rotting wood in place is just a work saving feature. If the wood is really rotten removing it can be as simple as drilling two holes and vacuuming it out (a piece of wire on a drill will turn it to dust beforehand if needed). Pressure washing it out is also an option but a really messy one. If the wood is only partially rotten removing it is more involved.

    What constitutes a cost effective repair depends on ones expectations. A boats value is not in her hull but in her systems. A sound but bare hull is worth nothing. This nothing only increases as the boat gets bigger. Every repair has to be valued against the boats total value.
    The classic example are sheated wooden boats. They were usually buildt with a 20-30 years life expectancy before major structural overhauls, and depending on owner care they reached and even surpassed that. But at some point in their life the needed repairs would have exceeded their market value and sometimes even the replacement value. But they still were functioning boats with nice interiors and good systems so they got sheated for little money and got a new life of 10-20 years. This was the most cost effective method then, and it still can be today. Of course 10-20 years after the sheating most boats are completley rotten (there are always exceptions). They can be repaired either by removing the fiberglass and replacing the wood, or by removing the wood and adding more fiberglass. But again this repair has to make some sense to someone.
     

  9. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    CPES comes to mind.

    Along with the banana smell...
     
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