Vinylester vs Epoxy on new plywood?

Discussion in 'Fiberglass and Composite Boat Building' started by ImaginaryNumber, Jun 16, 2017.

  1. ImaginaryNumber
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    ImaginaryNumber An Imaginary Member

    In the interest of saving money, can vinylester be used to replace epoxy when laminating fiberglass to new plywood? Will the vinylester be substantially as durable as epoxy? This would be for a new 24' catamaran.

    IF YES, can/should the vinylester/fiberglass be vacuum bagged or resin infused? Is it cost effective to purchase the vacuum equipment for a single project, vs using epoxy?

    If YES, can the vinylester/fiberglass be applied to the hull sides where the sides are more or less vertical? Or should the hull be rotated so that the working side is more or less horizontal?

    Are there online or print guides to the process, and selecting the proper resin and equipment, etc?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    What do the plans for the boat say regarding sheathing ?
     
  3. ImaginaryNumber
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    ImaginaryNumber An Imaginary Member

    The plans have not been purchased, but most designers specify epoxy. My question is generic -- can vinylester be economically substituted for epoxy when bonding fiberglass to plywood?
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Why sheath the boat with glass particularly ? Are you looking to increase the strength, rather than abrasion resistance ? The usual sheathing materials like dynel are basically used to give a tough skin, that is easier to apply than glass fabrics, and offers more abrasion resistance, the required strength and stiffness already provided by the structure.
     
  5. ImaginaryNumber
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    ImaginaryNumber An Imaginary Member

    Fiberglass is what I've typically seen listed in BOMs. Your suggesting using dynel in place of fiberglass is a different question than mine -- which is using vinylester vs epoxy? Is dynel compatible with vinylester?
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I am not suggesting anything, other than caution ! :) But I really would not trust a closely woven cloth of any kind to reliably bond directly to ply, other than with epoxy. A catamaran has a lot of corners, as well, and getting glass cloth to drape around them is another likely
    headache. The stretchy sheathing fabrics are less handicapped in that regard.
     
  7. gonzo
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    gonzo Senior Member

    If you use vinylester, the laminate will be heavier because ideally the first layer will be mat, which absorbs a lot of resin. Ultimately, if the laminate is structural, ask the designer for the equivalent schedule and compare total price and weight. As far as laminating over vertical panels, it is not a problem. It is possible to laminate overhead with a bit of planning.
     
  8. missinginaction
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    missinginaction Senior Member

    Epoxy is waterproof. Seven years ago I did a restoration of a fiberglass hull, wood deck/cabin cruiser. Last year I noticed a couple of cracks in the paint caused by two hard spots. When I did the repair on the original epoxy/glass sheathing I found absolutely no water intrusion anywhere in the deck. I had to grind out the area, pretty extensively, to make the repair. My understanding is that vinyl ester resins are better than polyester but still not as good as epoxy. Epoxy costs a bit more but it works. I won't use anything else.
    Follow the instructions given by PAR and others here. Three coats of resin on all 6 sides. Apply resin in time to get a chemical bond between coats. Apply sheathing, if desired, fill, fair and paint.
    Done right, done once and done for good.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Resin choices are application dependant, as you've seen. Polyester is at the bottom of the list, epoxy at the top with vinyl in between, but far better than polyester. Application technique (hand, bagged, etc.) can fall into what you're most comfortable with, but generally it's a weight savings (and some costs) thing. Intrusion will produce the lowest resin to fiber ratios, though most designs can't benefit from this. Bagging is more user friendly and better than hand laid laminates in terms of weight, fiber ratios, etc. A trained monkey can do hand laminates, which can be an advantage.

    The money you might save in resin costs comparing epoxy to vinyl isn't as much as you might think, I've found. As Gonzo points out, you'll use more resin with the alternating layers of mat with vinyl. Strength wise, all the resin systems can be used on a taped seam build, though the lightest (read less materials) will be epoxy. Additionally, shear strength on wood, particularly plywood with its "tabbing" and taped seams, using the other resins (poly, vinyl) will be weaker, unless the laminate is thicker/heavier to accommodate the modulus reduction, typical of these resin systems.

    Sheathings on the usual taped seam design is for abrasion protection and to some degree, improved waterproofing (especially along seams). Strength and stiffness requires much more laminate thickness than a light sheathing, so polyester and modi-acrylic fabrics (Dynel & Xynol) can be employed, knowing they're not adding anything other than improved abrasion resistance, compaired to 'glass fabrics. Most BOM's tend to employ commonly available fabrics, so this is why you see lots of cloth, but in many cases, you can decrease the laminate stack with biax in selected areas, which saves some resin and material.

    In the end, other than doing a laminate study, so see how much of what you might save is a crap shoot in regard to resin systems. Will you use less resin, maybe, maybe not, but does the savings get offset in thicker laminate stacks, when comparing apples to apples?
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    The way to go with a weight-critical application is epoxy. A catamaran is weight-sensitive, and has a lot of surface area to cover, in the long run the extra weight of resin-rich could cost in performance what you save in the initial $ outlay.
     
  11. ImaginaryNumber
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    ImaginaryNumber An Imaginary Member

    Thanks to all for sharing your experience. The consensus seems to be not to fool with vinylester and just use the proven epoxy.

    On to a different topic...

    Both Gonzo and PAR mentioned using a mat (which soaks up a lot of resin) when applying Dynel. What is the purpose of the mat? Must you use the mat anytime you use Dynel, or is the mat specific to a vinylester system?

    The catamaran designs I'm considering are all single or double chine plywood hulls (designs by Woods and Kohler, etc). Is the fiberglass (or dynel) sheathing generally just for abrasion resistance, or is it structural as well? If only for abrasion resistance are other fabrics (Dynel and Xynol have been mentioned) better than fiberglass? Or might it be best to cover the underwater hull sections with one fabric, and the topsides and decks with another fabric? Or maybe use a multi-fabric laminate?

    I know someone will say "ask the designer", and I will. But I'd like to first get myself up to speed on the options available.
     
  12. PAR
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    PAR Yacht Designer/Builder

    Mat is used on poly and vinylester resins, not epoxy and alternate with most laminate stacks using the polyester or vinyl. Mat isn't necessary on Xynole or Dynel. As mentioned, 'glass fabrics need to be relatively thick to offer some stiffness and strength to a sheet of plywood, so a typical sheathing is just abrasion resistance. Dynel and Xynole are solely abrasion resistance fabrics. As to the structural aspect, well yes, the taped seams form part of the hull shell and do contribute to the shells watertightness and stiffness, though much of this is in concert with the fillets and plywood, as a cured homogeneous unit. As to the laminate schedule, well you'd be best advised with the recommendations on the plans, though yes, with some experience you can change the stack to be more suitable to your needs.
     
  13. ondarvr
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    ondarvr Senior Member

    Sticking with epoxy (pun intended) is probably a good idea, but I'll add to the CSM and VE discussion.

    When hand laminating using CSM is important, but when infusing it's not needed in the same way.

    The reason for the CSM in hand lamination is the resin rich layer formed between the substrate or individual layers of glass, the loft of the fabric holds it up off the surface or interface, and with fewer fibers being in this zone it's weak and brittle. With infusion the layers of glass are consolidated very well so the fibers are very close to the substrate or each ply of glass, so there is no weak resin rich layer to fail. This helps make infusion much lighter for the same strength aside from just getting a better resin to glass ratio.

    Epoxy is strong enough to not fail in the resin rich zone.
     
    Last edited: Jun 19, 2017
  14. rwatson
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    rwatson Senior Member

    PS - Epoxy is the best solution as previously discussed, but please note - - Vinylester STINKS !!!.. If you can work in a shed that smells like someone has blowtorched a dozen plastic chairs for a week, you are a better man than me.
     

  15. ImaginaryNumber
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    ImaginaryNumber An Imaginary Member

    ondarvr,
    Thanks for the added information. I now understand more clearly what the purpose of the matting is.

    rwatson,
    I understood that the smell from vinylester was greatly reduced by using a bagging technique, which was why I asked about that in my initial query.

    I am wondering now if either the savings in epoxy resin cost or the enhanced fiber to resin ratio economically justifies vacuum bagging with epoxy. This would be for a recreational cruising catamaran, not a high-tech racing boat. I'm guessing not, so I should just embrace the KISS principle.
     
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