Yet another epoxy vs vinylester ...

Discussion in 'Fiberglass and Composite Boat Building' started by fcfc, Nov 3, 2011.

  1. fcfc
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    fcfc Senior Member

    I would like to know how epoxy and vinylester compare for the following points :

    -aspect and coating (print through, gelcoat ...)

    -structural bonding (ie structural bonding of 2 vinylester parts).

    -aging.


    What I am interested in is fatigue, aging, debonding and required maintenance (paint life, UV), in fact longuest useful life with minimum maintenance.

    Both would be used infused, and glass as only fiber.

    Thanks.
     
  2. Sand crab
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    Sand crab Junior Member

  3. ondarvr
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    ondarvr Senior Member

    You need to narrow it down on the exact formula of each product.

    While epoxies in general have superior properties when compare to VE's, this can change when you start using low viscosity infusion epoxies.

    As you lower the viscosity of epoxy to the point where it flows easily and infuses quickly, you also lower the physical properties rapidly. So depending on which epoxy you use for the comparison the epoxy may have lesser or greater physical properties than the VE.
     
  4. jim lee
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    jim lee Senior Member

    Really??! Now they tell me!

    -jim lee
     
  5. rwatson
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    rwatson Senior Member

    Well you havnt been following the dozens of threads on the Forum much, nor reading the actual tech sheets eg

    http://www.westsystem.com/ss/thinning-west-system-epoxy/

    "Thinning epoxy with solvent

    Adding solvent is a quick, simple method of thinning epoxy, but unlike using heat to thin it, the strength and moisture resistance of the cured epoxy are drastically affected. Below are some of the effects adding solvent has on WEST SYSTEM epoxy. While there are a large number of chemicals available to thin epoxy, we selected acetone, lacquer thinner and denatured alcohol for this discussion because they are commonly available and do a good job of reducing viscosity. Additionally, these solvents evaporate quickly and are less likely to be trapped in the cured epoxy—an important characteristic. For a variety of reasons, fast evaporating lacquer thinner appears to be more appropriate for thinning purposes than acetone or alcohol.

    * Adding a small amount of one of these solvents has a significant effect on the viscosity of the epoxy. For example, adding 5% lacquer thinner makes about a 60% reduction in viscosity (Figure 4).


    * Adding 5% lacquer thinner to epoxy reduces the epoxy’s compressive strength by 35%—a big hit in the mechanical properties of WEST SYSTEM epoxy (Figure 5). The addition of more than 5% solvent results in an excessively flexible cured material. Thinning epoxy with solvent causes enough loss of strength that we (and most other reputable epoxy formulators) cannot recommend using it as a structural adhesive.
    "
     
  6. jim lee
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    jim lee Senior Member

    We're taking about store bought infusion epoxy. Not "thin it yourself" epoxy. I'd figured store bought was going to be fine.

    Well, at least I was talking about store bought..

    -jim lee
     
  7. ondarvr
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    ondarvr Senior Member

    The manufactures have reactive and non reactive diluents to use in epoxy, they both reduce the physical properties, just at different rates.

    It's fairly easy to reduce the viscosity of polyesters and VE's to where they infuse with excellent results, epoxies tend to be much higher in viscosity to start with and can be difficult to get down to levels where large parts can be infused quickly. So when the viscosity of epoxy is lowered the strength can be reduced to levels closer to, or even lower than VE.

    This is why when someone asks about which type of resin is stronger for an infused hull you need to know the exact resin they plan to use.
     
  8. rwatson
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    rwatson Senior Member

    Fair enough Jim, but as i understood it, High Viscosity epoxies were just 'thinned' at the factory.

    I did a bit if checking though

    For example, West Systems only hi viscosity product G'Flex,

    http://www.westsystem.com/ss/typical-physical-properties/

    has much lower compression and tensile strength than their 'standard' range.
    eg Tensile 7846 to 3440

    I havnt looked up any other manufacturers, but I would expect to see similar figures - if they publish them. Some dont.
     
  9. ondarvr
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    ondarvr Senior Member

    G Flex is formulated for better adheshion and flex than a typical epoxy, this results in the lower physical properties.
     
  10. fcfc
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    fcfc Senior Member

    I fear my question are way more basic that that.

    It can be shortened to :

    How to structurally bond infused vinylester parts, at what price and long term reliability. Epoxy bonds ???? , bonding after cure ????

    How to coat infused epoxy parts, at what price and long term reliability. Gelcoat for epoxy ????

    Thanks.
     
  11. rwatson
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    rwatson Senior Member

    as Ondarvr mentions, the G'Flex by West Systems is especially designed to adhesion and flexibility.

    The other parts of your question are so dependent on the parts size, usage, shape etc etc

    its really not possible to get a detailed guide in this thread. You need to get local professional assesment.
     
  12. jim lee
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    jim lee Senior Member

    fcfc : Sorry about hijacking your thread there..

    Bonding infused vinylester parts : We use plexus for this. Works great, stinks horrible.

    -If- you use plexus and want to gelcoat over it, you need to coat the plexus with marine filler. It uses a different type of cataylst that is compatible to both chemicals. (Comp 1 guy told me this, seems to work.)

    If I was to infuse an epoxy part I would not use gelcoat, I'd just paint it. Gelcoat does not go over epoxy well. Not tried it, but everyone says it won't work.

    I've been told that they tried some sort of tie coat on the Farr 40s to infuse epoxy over gelcoat. It ended up a disaster. Basically the boat skins fell off after shipping to customers.

    Good luck!

    -jim lee
     
  13. idkfa
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    idkfa Senior Member

    Attached Files:

  14. jim lee
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    jim lee Senior Member

    "Recommended for building prototypes and scale models…"

    Doesn't leave you with a feeling of great confidence.

    -jim lee
     

  15. ondarvr
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    ondarvr Senior Member

    We make an epoxy compatible gel coat.

    When you say bonding do you mean gluing two laminates together, or laminating over an infused part?

    Gluing two pieces of VE together can be done with a VE adhesive (not putty), epoxy or a methacrylate.

    If you want to laminate over an infused VE part, just grind the surface, with the correct overlap it will be plenty strong.
     
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