could i use poly insteat of epoxy

Discussion in 'Materials' started by mkpardy, Jan 19, 2007.

  1. mkpardy
    Joined: Jan 2007
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    mkpardy Junior Member

    polyester resin


    thanks for input. i'm thinking of the glen l console skiff 15'6".
    what if i used 24oz roven as a layer along with a few layers of
    mat on the exterior and 2 or 3 layers of mat on the interior .also did i mention that poly resin is $28 gallon and epoxy is
    about $135 gallon. what do you think.and again thanks for the input
    its greatly apprecieted
  2. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    Yes, you can use polyester. It is, however, a much more finicky resin, harder to mix and harder to work with, and the fumes are somewhat nasty. It is also not as strong, durable or waterproof. But I've used it successfully on a similar boat. You just need to make sure you know exactly what you're doing and make sure your mixing ratios are PERFECT.
    Why would you want to use chop-strand mat? It's a weak, porous filler with little structural value. Plus it's a pain in the backside to wet out properly, and it sucks up far more resin than real cloth. The slight cost saving compared to real cloth is not worth the much greater hassle; I understand this is a stitch-and-glue boat and this technique works a lot better with moderately heavy cloths than with mat.
  3. fiberglass jack
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    fiberglass jack Senior Member

    poly resin will cure even if you dont have the ratio right, you have a lot of room to play with 1% to 2% just make sure you mix it well , alot of the resins will change color once catalised
  4. SamSam
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    SamSam Senior Member

    I think if a person is going to use polyester that the use of mat before cloth or woven roven and between the two is recommended to make them stick better without delamination. I've also 'heard' that csm is more waterproof when using poly, as water will wick alongside fibers and the nature of csm somewhat limits that as compared to continous fibers of cloth and wr. Sam
  5. dougfrolich
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    dougfrolich Senior Member

    Epoxy is a much better "glue", it is less brittle, much easier to work with, and much less nasty for your head (no styrene) you do not have to worry about the strength of your secondary bonds as much, you really do not need to use mat at all, I would use Epoxy for your project. it will be better and it is not like you need 100gallons--Live a little spend the extra $$.
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You will be much better off if using vinylester rather than polyester resin. It's much stronger and more water resistant. My God, 24 ounce roving, plus a few layers of mat, as well as the suggested laminate schedule for the inside (both of which will be quite heavy and relatively weak), you don't need the plywood stitch and glue parts for that layup!

    Not for nothing, but stick with the plans or very close to them. The engineered structures (like the laminate schedule, for one) isn't particularly tolerant of heavy deviation. As suggested, your boat will be much heavier (read, less load carrying capacity, lack luster performance, ill handling, etc.) likely quite brittle and not as strong as the suggested arrangement set down in the plans.

    Over building (for what ever reason) is the hall mark of home built boats and what usually is their biggest problem. Weight will kill the abilities of a small boat real quick. Making things thicker, stouter or of heavier construction, in the hope it will be a stronger craft, just isn't the case for the most part. It's a physics thing and does require substantial understanding, before changes like this can be thought through.

    Stitch and glue boat construction exists only because of the properties of epoxy, it's related reinforcements (fillers) and 'glass cloth. Without epoxy, there would be no real stitch and glue methods. That's how much better a resin it is, compared to other types used in the industry.

    You don't have to use $135 per gallon of goo, do a search for epoxy and you'll find some at much less then that. Also, skip the mat, use cloth as mat is just a bulking material and offers little in the strength department.
  7. jimslade
    Joined: Aug 2005
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    jimslade Senior Member

    If you use marine ply, stay away from poly. The oil in the ply does'nt like poly. If it's regular ply you could go with a good isophalic poly. It's a little better than an orthophalic resin
  8. JR-Shine
    Joined: May 2004
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    JR-Shine SHINE

    Also, you can buy good epoxy for half what you list.

    Mat soaks up resin (poly or epoxy), so it soaks up your $$$ also without providing much strength.

    If the designer depends on the far superior bonding of the epoxy, then there could be trouble in substituting poly.

  9. compwest boats
    Joined: Mar 2004
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    compwest boats Junior Member

    ..not simple math!!

    ....the superior strength,,bond,,flexibility of epoxy will allow ~50% less mass of cloth,,and therefore a LOT less resin will be used,,,,,and therefore significantly less weight in your final product,,,so you need to factor the fuel-cost saved for years into the budget choice:p
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