PVA + Gelcoat in mould, for adhesion to epoxy laminate

Discussion in 'Materials' started by idkfa, Dec 20, 2016.

  1. idkfa
    Joined: Sep 2005
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    Location: Windward islands, Caribbean

    idkfa Senior Member

    Since epoxy is used to bond polyester parts together... Epoxy laminate over gelcoat in mould should be fine.

    But it isnt,

    Unwaxed gelcoat is used in moulds, so the surface cures very slowly, presenting ready bond for polyester laminate...

    Waxed gelcoat in a mould will cure, in hrs... but then there is wax inhibiting laminate bond....

    What if PVA is used over the gelcoat... it will fully cure, allowing for good adhesion to epoxy laminate????...with some light sanding to key surface.
     
  2. ondarvr
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    ondarvr Senior Member

    And...you need to wash the PVA off with water, then sand.

    There are epoxy compatible gel coats.
     
  3. idkfa
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    idkfa Senior Member

    Guess I'm testing the premise that chemically gelcoat is coloured, thickened polyester resin....

    Cause all polyester laminates are compatible with epoxy.... if surface preped correctly...

    Then all gelcoats are also compatible with epoxy....

    In a commerical setting, no one is going to PVA-sand or use peelply...Hence the "compatibility" problems.

    But for smaller parts PVA is an option. Tks
     
  4. ondarvr
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    ondarvr Senior Member

    What I'm saying is that while yes it could be done, there are much easier ways to get a gel coat finish on an epoxy part.

    Duratec products are designed for this type of application, they cure tack free for in-mold use with epoxy (they work with Polyester and VE too).
     
  5. Jim Caldwell
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    Jim Caldwell Senior Member

    I was told epoxy only bonds well to old polyester products as in no strine smell.
     
  6. trekker
    Joined: Jan 2016
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    trekker Junior Member

    In a mold, would an epoxy lamimate bond better to poly gelcoat that has had the Duratec high gloss additive mixed in?
     
  7. ondarvr
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    ondarvr Senior Member

    You need to add enough for the surface to cure tack free, or just use a high ratio of clear additive in the final pass.
     
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  8. PBC
    Joined: Aug 2020
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    Location: South Africa

    PBC Junior Member

    50FDD68F-4BBF-46B7-B23A-BB9611E1B76F.png
    Hi Ondarvr,
    I am looking to infuse epoxy over gelcoat for my hull. What Duratec product would you recommend. I can get Duratec products but can’t find a epoxy compatible gelcoat that is UV stable and can be submerged in water for long periods. I was looking at Duratec Sunshield but this is expensive. It sounds like you are talking about a Duratec product that can be added to polyester gelcoat to make it compatible with epoxy? Is this the product below?
    Thanks
     
    Last edited: Sep 5, 2021
  9. ondarvr
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    ondarvr Senior Member

    What size boat and will it be kept on a trailer or in the water for extended periods of time?
     
  10. PBC
    Joined: Aug 2020
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    Location: South Africa

    PBC Junior Member

    24.5 foot boat. It will be a production boat. So some will live on trailers and others will live on a mooring so will be in water for extended periods.
    Thanks
     

  11. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    Constant immersion is the toughest situation, it tests the bond more than anything else.

    You need to test it with the exact epoxy you plan to use, not all epoxies are created equal.
     
    trekker likes this.
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