polyester resin stitch and glue

Discussion in 'Boatbuilding' started by Jamesblack, Aug 16, 2013.

  1. Jamesblack
    Joined: Jun 2013
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    Location: Victoria, Australia

    Jamesblack Junior Member

    can polyester resin be used instead of epoxy resin for a low cost stitch and glue boat? it costs about half as much.

    i'm sure it cant be used, but all help is appreciated
    thanks
     
  2. lewisboats
    Joined: Oct 2002
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    lewisboats Obsessed Member

    You can use poly to tape the seams but it is not a good substitute for epoxy as a filleting material (it is a crappy glue)... and that is half of the stitch and glue process. Substituting a chine log as your inner support with tape and poly on the outside to seal the deal is OK. You should make sure the surface is very clean and roughened up with something like 80 grit paper, especially across the grain of the ply to scratch it up properly so the poly can bond. If the design isn't too radical, with fairly smooth curves or straights to the panel edges then adapting a chine log is a fairly straight forward process. You stitch the sides, transom and bow together, spaced with some temp spreaders, fit the chine logs so they extend past the edges of the sides, get your bottom ready to go on and then pare away the chine logs with a plane until the bottom fits. If it is a Vee bottom you will have to deal with the centerline seam too, but shaping a chunk of 2x to fit as a keelson is just a matter of paring and fitting also. Of course... if you weigh time vs money... enough epoxy to do the filleting then poly for the taping might be the better option... costing more but only for a portion of the total amount of resin needed/used.
     
  3. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Epoxy is a relatively recent invention, and literally thousands of 'stitch 'n glue' boats were built in the 60's and 70's with glass tape and polyester resin.
    One of the best known perhaps being the Mirror dinghy - they were all built from kits, and I think at least 50,000 were produced.

    But they only used polyester resin because there wasn't anything better available at the time.

    In the grand scheme of things, when you consider all the advantages of epoxy over polyester, it is well worthwhile spending a bit more on the epoxy.
     
  4. El_Guero

    El_Guero Previous Member

  5. Chenier
    Joined: Oct 2012
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    Chenier Junior Member

    Pardon me, I posted to the wrong thread!
     
    Last edited: Aug 17, 2013
  6. PAR
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    PAR Yacht Designer/Builder

    This is completely incorrect. Epoxy in it's original forms (bisphenol-A) where developed in WWII, though epichlorohydrin derived formulations date back to 1937. Polyesters developed slightly before, with a Dupont patent in 1936, but the first real modern formulation (recognizable formulation) was 1942 and was easier and cheaper to formulate, so it's adoption into manufacturing processes came quickly (Arion in 1951 was the first production run, though several small one offs where done as far back as 1943). The Gougeon brothers started decanting epoxy in 1958 and had their first boat built, using epoxy as an adhesive only in 1960. This was typical of early epoxy formulations. In the 60's epoxy viscosity modifiers, became commonly employed and tapes seam building as well as coatings took off, once engineers understood the concepts (early 70's). Previous attempts with polyester littered the marinas of the world for a few decades, eventually getting plowed under in land fills in the 80's and 90's. In fact, tapes seam building didn't gain any real acceptance until epoxy was employed and a reliable bond could be had on wood, which polyester repeatably proved wasn't possible. There would be no taped seam industry without epoxy.

    So, to answer the question, sure you can use polyester and a few diehards insist it can work, but the physical attributes of these two resin systems are well known and epoxy is the only real choice, in a taped seam build with wooden substrates.
     
  7. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Ummm, I did say 'relatively'...... :)
    But it would have been more accurate if I had instead said that epoxy has become popular for stitch and glue construction relatively recently.
    I have a copy of 'Build The New Instant Boats' by Dynamite Payson from 1985, and although he does acknowledge epoxy, all of his boats then were built with polyester resin and glass tape.

    Mirror dinghies are still being built in England now, but mostly in fibreglass rather than plywood, although plywood kits are still available -
    www.mirrorsailing.org/buy.asp
    I am sure that they must have made the transition from polyester to epoxy at some stage on the plywood kits, but I suspect it was probably fairly late - my Dad built a Mirror from a kit in the mid 60's, and even then the sail number was almost 11,000 (and they are up around 70,000 now - although I am sure that almost all of the early Mirrors have fallen apart by now).

    Epoxy is definitely the way to go now though - James, don't even think about polyester! Although epoxy costs twice as much, I don't think that epoxy prices have increased much over the years, at least not here. A gallon cost about US$200 here 15 years ago, and still is around that (perhaps due to more competition?), whereas the cost of polyester here has more than doubled, making the difference much smaller.
     
  8. pauloman
    Joined: Jun 2010
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    Location: New Hampshire

    pauloman Epoxy Vendor

    polyester resin tends to disbond from wood in 5 -10 years (from my experience and that of my customers). There is a reason why fiberglass boats are 100% fiberglass - polyester resin only bonds well to itself.

    Paul Oman - MS. MBA
    A.K.A. “Professor E. Poxy”
    www.epoxyfacts.com
    epoxies since 1994
    Member: NACE (National Assoc. of Corrosion Engineers) -- SSPC (Soc. of Protective Coatings)
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    From a technical stand point, polyester doesn't bond to itself very well, though sufficiently enough. Epoxy bonds to polyester better then polyester bods to itself.

    I guess relative is a relative term, as after 30 to 40 years of implementation, I consider this pretty well established. Payson was a dieheard about polyester, but just one of the few. His techniques produced much heavier products then that done in epoxy. He had good results, but again it came at a cost.
     
  10. Jamesblack
    Joined: Jun 2013
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    Jamesblack Junior Member

    i think i will 'stick' with epoxy then. thanks for all the help
     
    1 person likes this.
  11. Vulkyn
    Joined: Jun 2010
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    Vulkyn Senior Member

    Well the more experienced members have replied, i have indeed came across boat builders in Egypt that do exactly that. My boat is built by them the same way with polyresin and fibreglass but as indicated its only used for wetting the fibreglass not as glue or filler.

    The boats will have a relatively short life span and it will not be of high quality, but it works to a degree and its very cheap as well. (I will eventually build a proper boat with epoxy but this was a stepping stone ... )

    I have attached some pictures ...
     

    Attached Files:

  12. ancient kayaker
    Joined: Aug 2006
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    ancient kayaker aka Terry Haines

    Steve gave good advice in post #2, use chine logs. The wood is probably cheaper than fillets, the method is faster than taping and the results looks great without hours of sanding. The skill to make neat fillets eventually comes but not with the first boat!

    Depending on what size boat you are making, for smaller sizes (canoes, small row and sailboats) the logs can be glued to the sheer planks while flat but once the boat gets too big it becomes too difficult to bend the stiffened plank to shape.

    If you really don't care about appearances or the inside is not visible, there's really no reason why a chine log should be one continuous piece - it can just be a series of short blocks installed after stitching the planks together, instead of glass tape. To reduce weight or make applying glass clth to the inside easier, the log or blocks can be triagular section or even concave (arris).
     
  13. El_Guero

    El_Guero Previous Member

    AK,

    So you would use the chine log like a stringer?
     
  14. ancient kayaker
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    ancient kayaker aka Terry Haines

    Not the same thing, is it? Stringer supports mid-plank, chine log reinforces joint between planks. Or did I misunderstand the question . . . ?
     

  15. El_Guero

    El_Guero Previous Member

    You got the question, I still do not know all of the terms.

    OK, so it would run longitudinally, like a stringer would. But, would give support in a different place, for a different reason.

    Would you screw these in place, or epoxy, or both?

    And would using ribs and stringers give that much additional support that they would be worth the extra effort - completely different question.

    Thanks

    wayne
     
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