Fiber glass resin bare in water?

Discussion in 'Materials' started by Matthew petruescu, Jul 14, 2020.

  1. Matthew petruescu
    Joined: Jul 2020
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    Matthew petruescu New Member

    Hello. Im doing some work on my boat on the outside and using fiberglass repair with epoxy. I was wondering do i have to lay down Gel coat before going into water on the fiberglass resin. Or can I go in bare with my epoxy fiberglass resin thing.? Just wondering because I want to go out in the water already and do the gel coat in a week or two
     
  2. ondarvr
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    ondarvr Senior Member

    You don't need to coat it right away, but....

    Epoxy has very poor UV resistance, so if this area is in direct sunlight it will turn yellow and over time it will degrade the resin.

    Even just a coat of some cheap rattle can paint will protect it.
     
  3. fallguy
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    fallguy Senior Member

    I thought poly gelcoat was a no-no on epoxy, too.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    I wonder why epoxy is being used for the repair.
     
  5. DCockey
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    DCockey Senior Member

    fallguy likes this.
  6. gonzo
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    gonzo Senior Member

    Polyester gelcoat works fine over epoxy as long as it gets properly clean and de-waxed. I have experimented with it and after several years it is holding.
     
  7. ondarvr
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    ondarvr Senior Member

    We sell polyester and VE products that are epoxy compatible, they work both in-mold, and post applied to epoxy.

    Here's the thing, in an uncured state the two different chemistries are not compatible.

    So a full cure is required for a good bond. If the epoxy isn't fully cured for any reason, the gel coat won't bond that well.

    Also, I've run into epoxies that other coatings won't stick to very well. These were mostly special epoxy formulations for certain high temp applications.

    So while normal gel coat can frequently work good enough over epoxy, it's not a sure thing. Some gel coats and some epoxies just don't play well together, and not every combination can be tested.

    There are enough failures that people shy away from recommending using the two together.
     
  8. fallguy
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    fallguy Senior Member

    This is helpful. At least I am not going insane as I was sure I had read/was told to not gelcoat my boat.
     
  9. gonzo
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    gonzo Senior Member

    I was told and also read the same advice. However, no one could tell me of any tests that proved their opinion. Instead of believing blindly, I gelcoat over a large epoxy repair on a boat that was given to me as a trade-in for an engine installation. It had a large hole (3' by 5') and several small ones. I patched them and gelcoated over 11 years ago. The gelcoat has not peeled, cracked or otherwise exhibited any other defect, except for fading due to UV.
     

  10. ondarvr
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    ondarvr Senior Member

    I've done the testing, and had both good and bad results. More good than bad, but some were complete failures.
     
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