epoxy and poly?

Discussion in 'Fiberglass and Composite Boat Building' started by COLD-EH', Dec 11, 2005.

  1. COLD-EH'
    Joined: Dec 2005
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    Location: Edmonton, Alberta, Canada

    COLD-EH' Junior Member

    I was thinking about doing a "STYROFOAM" one off hull and since epoxy is expensive I was wondering if after you had a layer of epoxy/glass on the foam if there is any negative problems to switching to poly? Adhesion etc. Epoxy would glue everything together and prevent melting of the foam and do the buildup with poly. I'm sure I read about a Vancouver manufacture that was using poly for main mass and covering with epoxy for water protection. Epoxy in this situation would have a different role but therefor don't see adhesion being a problem. What do you think?
     
  2. Deering
    Joined: Feb 2005
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    Location: Juneau, Alaska

    Deering Senior Member

    There's a couple problems with your plan:

    1. Epoxy sticks fine to poly with some surface prep. Poly does NOT stick fine to epoxy. You'll have delamination nightmares.

    2. Styrofoam probably isn't the material you want to use for a core. A foam core generally needs good shear stress characteristics. Get the physical properties for the styrofoam you plan to use off of the manufacturer's web site. Compare them to a foam designed for this purpose - Airex or Corecell for instance - you'll find that there's a big difference in the strength properties of these materials. It might work for awhile in a low-demand application... but it might not.

    Consider your time on this project. It's usually worth a lot more than the material costs. Do you want to spend all that time only to have a material failure? Lots of opportunities to be innovative with boats - that's why most of us mess with them - but going too cheap on materials seldom pays off.
     
  3. skoc
    Joined: May 2005
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    Location: Croatia

    skoc New Member

    Beside a mechanical properties, big disadvantage of polystyrene foam is lack of any resistance to organic solvent, e.g., MEK, styrol (in polyester resin), gasoline etc.

    Skoc
     
  4. thesom
    Joined: Nov 2005
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    Location: greece

    thesom Junior Member

    You are lucky, I am doing this time my thesis about "Application and Maintenance of Marine Coating System

    You should use epoxy polyamide which fits good with a previous coating such as
    acrylic, alkyd, or urethane.

    Epoxy has good adhesion, flexibility and hardness and also a very good resistance to heat,abrasion,strong solvents etc But NOT to UV radiation.
    And of course epoxy has unlimited colour availability.
     
  5. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    In the long term, you're considerably better off to splurge on the epoxy. It's simply a better resin. It's stronger, more reliable, doesn't require nearly as much care in mixing and is much less sensitive to temperature and humidity than the ester-based resins. Not to mention it won't dissolve foam. What exactly are you thinking of doing with the foam- using it as a core, or using it as a plug?
     
  6. COLD-EH'
    Joined: Dec 2005
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    Location: Edmonton, Alberta, Canada

    COLD-EH' Junior Member

    I was going to use it as a core, I saw some articles on the subject on this site and I thought it was an interesting option. Same thing my thoughts for "Styrofoam" instead of "Corcell" or other core materials designed for the purpose was economy. I think I will stick with plywood for this one. I already have a ski boat for the lake but I want this one for home as I live a block from the boat launch on the river. I thought an airboat would be cool as I don't like the maintanance costs ive seen when the jets suck rocks. I used epoxy on a really big repair on my ski boat, 2 lift strakes cracked open 4 feet long. Lots of delamination and the stringers wern't even really held in by the chopped glass. AND a pool of clear resin at the back of the boat from running off the chop.That boat was built like crap, some people just don't have any pride in workmanship.The epoxy was great to work with and it's a better boat than it was originally however unless I can find epoxy at a better price I'll have to go with poly. Only so much disposable income to go around with a wife and 3 kids!
     
  7. makeitfly
    Joined: Dec 2005
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    Location: new zealand

    makeitfly Junior Member

    poly, vinyl, epoxy,

    Resins usage should go in the order above . Poly is the bottom of the scale on quality , Vinylester is in the middle and has a lot going for it . Epoxy is the top of the heap .
    Remember . Vinylester and polyester dont adhere to epoxy . Polyester dosent adhere to vinylester. I know i am going to be shot at for these comments .
     
  8. War Whoop
    Joined: Jun 2003
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    War Whoop Senior Member

    Some of the CNC guys use a Styrofoam armature (cost effective)once cut to say shape one then coated with epoxy , now a coupling agent is applied I have used clear dura tec before after that a polyester putty sprayed on that is machined and dura tec for the final surface. As for the compatibility of vinyl ester there are many boats out there with a vinyl ester skin-out and a polyester build up it works fine!
     
  9. zerogara
    Joined: Aug 2004
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    Location: Preveza

    zerogara build it and sail it

    Using styrofoam as a structural core is probably as good as not usuing a core at all. It might be helpfull as a boyancy or filling voids to form the outer skin of stringers but you should keep in mind that the only strength you have is the skin.
    Any shear will make it disintigrate or compress to the point it will delaminate from the one or the other side of the skin, or separate in two pieces itself. Polyurethane is really worth its higher cost, as long as you know which density and what qualities to use at the right place.
    I used styrofoam a couple of times in my earlier days of experimenting with plug materials (insulation panels) and the amount of work to prepare and fill imperfections and have them crack at the last phase of mold making was not worth its while.
     

  10. War Whoop
    Joined: Jun 2003
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    Location: Sunny Ft Lauderdale Fla

    War Whoop Senior Member

    Like I said some of the CNC guys use a Styrofoam built up armature using spray PU to “Glue” the blocks together as long as it is handled by professionals it works just fine! I have done a couple sets of tooling 38’ and 41’ with the plugs having that exact build-up… The ones I had problems with were the ones done with spray PU foam!!
     
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