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  • John B. Trussell
    I have an intuitive concern about mixing epoxy and polyester resins, but... I build a number of boats in the early 70 s using stitch and glue and stripper
    Message 1 of 4 , Dec 29, 2005
      I have an intuitive concern about mixing epoxy and polyester resins, but...

      I build a number of boats in the early 70's using stitch and glue and
      "stripper" construction, using polyester resin. The boats in question were
      kayaks and canoes used in white water which is fairly abusive. I punched
      holes and abraded the boats, but I never experienced any failure of a
      polyester/glass cloth/plywood matrix.

      I think the problem of bubbles when saturating glass cloth with epoxy are
      caused by the absorption of resin by the softer areas of the plywood veneer.
      A solution is to seal the plywood before applying the cloth. Perhaps the
      best way to do this is to apply a coat of epoxy resin to the hull, let it
      cure, sand it smooth, wash it, dry it, and then apply the glass cloth and
      epoxy resin.

      I periodically shoot off about material costs being only a small fraction of
      the total cost of building a boat and how it makes sense to use the best
      materials. There have been periods in my life when this was not an option
      and the choice was to go cheap or not build at all. If I were forced to
      economize in a boat building project, I would give serious thought to
      substituting polyester for epoxy in stitch and glue construction and using
      powdered weldwood for those parts that needed to be glued. I will not argue
      that either of these products is superior to epoxy (they aren't), but they
      are good enough and they are a lot cheaper than epoxy.

      For what it is worth, filling, sanding, and painting are my least favorite
      parts of boat building, and I do everything possible tomake the process as
      short as possible. I find that it is easier to fill and grind down
      imperfections before I start applying finish coats (and fg sheathing is the
      start of a finish coat). The idea is to have smaller imperfections at each
      level of the finish until the imperfections disappear or (in my case) you
      say, "Hell with it; that's good enough!"

      John T
      ----- Original Message -----
      From: "Nels" <arvent@...>
      To: <bolger@yahoogroups.com>
      Sent: Thursday, December 29, 2005 11:00 AM
      Subject: [bolger] Re: QUESTION ON GLASSING

      > --- In bolger@yahoogroups.com, James Greene <jg6892@g...> wrote:
      >> On Tue, 27 Dec 2005 20:39:09 -0000, Richard Jernigan wrote:
      >> > I've found that I have better luck with avoiding gaps and voids if
      >> > I coat the wood or plywood with kicked polyester resin and allow
      > it to
      >> > cure before coating with epoxee and glass.
      >> I would never do this. Epoxy is an adhesive, polyester is not.
      > Epoxy bonds far better to wood than polyester. I think you're
      > sacrificing structural integrity and/or longevity for a nice finish.
      > Sorry to disagree with your technique, but that's just how I feel. Of
      > course I could be wrong ...
      >> James Greene
      > Here is what the Cold Cure manual says...
      > "Cold Cure epoxy is a much better choice over wood than polyester
      > resin. Polyester is a poor adhesive because it shrinks and delaminates
      > then it lets moisture get between the fiberglas and the wood
      > substrate."
      > Obviously this is a biased comment since the makers of Cold Cure wrote
      > the manual. And Dynamite Payson used polyester for glassing his line
      > of small Bolger boats for years and many of them are still going.
      > However he now recommends using epoxy instead.
      > My understanding is that epoxy is composed of a smaller molecular
      > structure than polyester resin and is able to make a more even and
      > waterproof bond with the cellular structure of wood than polyester
      > resin and therefor has a stronger bond. This claim was made by Ted
      > Moores, considered a "guru" in the cedar strip canoe building realm.
      > http://www.bearmountainboats.com/
      > The Cold Cure manual also shows how to do your own testing to see
      > which choice of methods works best for your particular combination of
      > materials. Take some small pieces of your chosen plywood and laminate
      > strips of glass onto them, leaving the strip loose on one end so you
      > can grab with some pliers and see which choice adheres to the wood
      > best.
      > Nels
      > Bolger rules!!!
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      > - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax:
      > (978) 282-1349
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