Soft wood epoxy soak

Discussion in 'Boatbuilding' started by nedgrater, Sep 1, 2009.

  1. PAR
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    PAR Yacht Designer/Builder

    As I mentioned in a previous post. Reheating is self defeating and likely driving out resin, not letting more in. I guess it depends on how badly you'd like this to succeed.
     
  2. nedgrater
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    nedgrater Junior Member

    Test results-
    In short the vaccum method did the job.... brilliantly.
    Thanks for the help as it really wouldn't have occured to me to use this method.
    I was particually suprised because I have vaced on balsa before and don't remember the balsa skins becoming satuarated.
    I did a few different tests and as most of you said penetraing epoxy does nothing for strength... True.
    I think the exact method I will use when I do it for real is to heat the wood before I epoxy, to drive out any moisture, warm the epoxy so the viscosity is a little less then apply very librally to the wood, then get it in the bag asp.
    The test peice was so good the 2mm poplar wood was 100% saturated and tough as old boots.
    many thanks I'm a happy man!
     
  3. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I imagine pressurizing the camber would increase the pentration

    for the same reason that using a vacuum starting at low pressure would be less effective.

    Less 'air' to replace.
     
  4. nedgrater
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    nedgrater Junior Member

    Hey Squidly Diddly, Wow, I think I follow what you saying.... This is crazy stuff!
    So if I pressurize the wood in a chamber before painting with epoxy and putting in a vac bag the vaccum would be more effective....
    This had definatly never occured to me.
    Wouldn't the whole room need to be pressurised though because as soon as you take the wood out of the chamber the pressure would release back to your local atmospheric pressure and the vacumm not be any more effective, or would the wood stay pressurized some how?
    This is a very interesting concept though, have I got the gist of what your saying or am I off track?
     
  5. rwatson
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    rwatson Senior Member

    I have no idea what Mr Sq was trying to say, but if you take the wood out of a Vac, it would not "stay pressurized some how"

    But I think it would have removed a lot of the water already, so during the "real" pressurisation that should allow an even better penetraton I would suspect.

    I am following your experimentaion with real interest. What it would mean is that a lot poorer woods can be used for boatbuilding, and considering the prices of "good" woods, that aint a bad thing
     
  6. PAR
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    PAR Yacht Designer/Builder

    To dispel some disinformation and misunderstanding of what is actually happening.

    In a vacuum bag you aren't placing the goo in a "suction" type of environment, you are placing it under pressure and frankly lots of it. The pressure comes from the atmosphere bearing down on the bag. Pulling 15 PSI on a pump seems like it's not much, but it's over one atmosphere and if you think about it differently, it's over a ton per sq. foot (2,160 PSI). Now that is a lot of pressure.

    Heating the wood causes the wood and the things inside the wood to expand. When epoxy is applied and most importantly (as I mentioned earlier) the wood is cooling down, the now contracting wood fibers and cellular structure will draw in epoxy, if it's viscosity is low enough.

    You can improve (lower) the epoxy viscosity by heating, of course at the risk of kicking it off much faster.

    There is no benefit to reheating the wood or epoxy, in fact there is a high potential for problems if you do so.

    Again, none of this is new and all is covered in several texts and manufacture's "product user guides".

    The "restored" wood, isn't restored at all. It's still the weak knee, red headed step sister to it's former self, but the surface and several mils into the surface have been soaked with epoxy, which makes it seem as if it's tougher. You'll find, under reasonable testing, very little of the physical qualities have been returned to the wood. It will be a fraction of it's former, compressive, tension, elongation, etc., strength self, though it's surface will be considerably better then the rotted mess it once was, not even remotely close to an "intact" piece.
     
  7. rwatson
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    rwatson Senior Member

    I dont think this bit is on subject. He is not restoring rotten timber, he is strengthening soft timber.

    The concept has protential for being able to utilize soft timber in higher exposure areas.

    Many timbers have excellent strength, but low endurance in marine environments. This might be a usefull technique given how expensive timber is these days
     
  8. PAR
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    PAR Yacht Designer/Builder

    Think of this treatment as the crust on a loaf of bread. Trust me, nothing is strengthened, it's just a surface treatment. Rap it with a knuckle and you'll find the real story, let alone give it a good swat with anything firmer then mashed potatoes.
     
  9. rwatson
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    rwatson Senior Member

    Hmm, I respect your point of view Par, but I cant see that having an incompressable, waterprooof coating on both sides of a piece of Poplar wouldnt represent a significant improvement.

    Everyone knows that a coating of just epoxy will crack if banged (the loaf of bread analogy), but if he is getting 2mm of impregnation, then the timber will be contributing with its fibres to form much more than a crust. It certainly wont just sheer off the surface when the wood is bent.

    But, I await further testing and evidence with interest.
     
  10. nedgrater
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    nedgrater Junior Member

    Hi, Yes I agree it is just a surface treatment, but what I wanted it for was give dent resistance to new 2mm poplar strutural venner and it penetrated it completely. This is great for what I want to use it for and I am not looking for the timber to provide any real strength, (that is provided elswere).
    I think this could have lots of uses though, for example, as a core material for sandwich contruction, as epoxy saturated poplar seams alot more durable than corecell or most PVC foams, and heaps cheeper too.
    I have not tryed it on any thicker peices of timber yet, but because of the good results so far I think I and going to do some more experments.
    I imagine different timbers will give very different results and I imagine softer wood will give better results because there is more air and possibly moisture to extract to be replaced with epoxy.
    I'm just doing some experments here, I'm not saying what I'm doing is right or even good practice, I'm just grateful of the advice you have given me so far.
    Thanks
     
  11. PAR
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    PAR Yacht Designer/Builder

    Core materials are selected for a few basic physical attributes. Light weight, an ability to accept the epoxy bond, peel strength from it's sheathing and most importantly compressive strength, which is why balsa is so widely used.
     

  12. hoytedow
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    hoytedow Wood Butcher

    Is it too late to go to a harder wood? Oak is harder and more open grained at comparable price. You didn't say what is the function of the piece.
     
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