Thinning polyester resin for penetration

Discussion in 'Materials' started by Owly, Sep 6, 2017.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    Thanks ondarvr. I guess the best plan if attempting to get better adhesion, is to test the materials on the particular timber substrate first, on a small scale first. I have heard of Duratec, slipped the mind.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    I am thinking of applications where lessening the prospects of delamination of GRP from ply is desirable. It certainly seems an easy precaution to have a more penetrating priming coat. Waterproofing can be attended to by other coatings.
     
  3. PAR
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    PAR Yacht Designer/Builder

    This debate has been ongoing for some decades, but testing has proven penetration with diluted resins doesn't do much. Those that haven't performed the tests continue the argument, but I've done is several times and the results always fall in line with industry results. This said, if you can use a non-reactive diluent, then penetration has some merit, but not as much as you might think. The problem is, when you thin a resin, you lower, usually dramatically its physical attributes, so it's grip, though deeper into the substrate is actually weaker. There are "lines" you can stay below in regard to dilution, while retaining enough of the tensional modulus, but it's not much of a cut. In most cases (resin formulations) once you go much over 10%, you've weakened the goo by as much as 50% (depends on formulation). Then there's the overcoat issue that you've mentioned. The over coat (waterproof or not) has to "tie" to this weakened resin on and in the substrate. This is an over simplification to the discussion, though the premises are valid and supported by testing.

    If you want to improve the polyester bond with plywood, use a better resin.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Ondarvr is talking about specific products that have low viscosity, not thinned laminating resins, as I understand it, but I'd want to see how it fared comparatively on a batch of ply before declaring it an improvement.
     
  5. PAR
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    PAR Yacht Designer/Builder

    I understand what David is saying, I'm just saying penetration has little to do with anything, except perception or as a marketing ploy. Lower viscosity resin systems do penetrate better, but it's a moot point, in terms of subsequent bonding needs. With polyester products, it would be wise to conduct a few tests to see which resin maintained reasonable tensional modulus.
     
  6. ondarvr
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    ondarvr Senior Member

    I wouldn't say these sealers do much to increase the water resistance, that's not their intended purpose.
     

  7. ondarvr
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    ondarvr Senior Member

    Got interrupted, had to get on the plane in Shanghai

    They're used to improve surface profile and bonding of top coats. On MDF or other wood plugs and shapes they help prevent changes in the dimensions and shape due to humidify fluctuations.

    I guess short term you could say they are waterproof, but nothing like epoxy.
     
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