Gelcoat problem after releasing a rim from the mold

Discussion in 'Fiberglass and Composite Boat Building' started by mrdebian, Jan 19, 2022.

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  1. mrdebian
    Joined: Apr 2021
    Posts: 98
    Likes: 11, Points: 8
    Location: Greece

    mrdebian Junior Member

    Hi all,

    I got a kayak rim out of the mold today and was horrible. Like it has pumps all over it plus a few more signs in the gelcoat. Anyone with an idea why that happened?

    I added two coats of gelcoat on this (by brush) with no lower than 2% catalyst. The first left 12 hours to cure and the 2nd less. The second was a tiny bit of gelcoat to solve here and there some places that it wasn't enough in the first coat.
    Any ideas?

    Thanks
     

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  2. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Pre-release, if gel coat is left sitting on the mold for extended periods of time it's not uncommon. And having odd shapes and contours can make it more likely.

    Apply the two coats of gel coat closer together, and put the laminate on the same day.
     
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  3. mrdebian
    Joined: Apr 2021
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    Likes: 11, Points: 8
    Location: Greece

    mrdebian Junior Member

    Thank you @ondarvr
    I will try as you suggested and see how it goes.
    May I ask please also what is the recommended time to leave it to the mold until I release it?
    It is a small mold for the rim and after a couple of hours (12 more or less) on it under 60-61F it looks really solid. Would it cause a problem to release it after that amount of time or is recommended up to 24 hours?
     
  4. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    I would wait for 24 hours, but the time-frame can vary a great deal depending on the exact resin.
     
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  5. mrdebian
    Joined: Apr 2021
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    Location: Greece

    mrdebian Junior Member

    @ondarvr just an update to say thanks a lot. The problem was exactly what you were outlined; pre-release.
    I've build 8 of them after that and all came fine.

    One more question please. What is the recommend time between applying a second layer of gelcoat in more or less 60F (16oC)?
     
  6. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    There are too many variables involved, exact gel coat, exact catalyst, catalyst percent, humidity, how thick it was applied, etc.

    If it doesn't come off on your finger you're typically safe, but thin areas will take longer, so check many locations.

    At 60F it can be a few hours sometimes.
     
    Last edited: Mar 18, 2022
  7. mrdebian
    Joined: Apr 2021
    Posts: 98
    Likes: 11, Points: 8
    Location: Greece

    mrdebian Junior Member

    At 60f the black gel coat that I used last time in 4 hours it was completely dry. I get the 16f with air conditioning so no humid at all as it dries the atmosphere.
    That was with 2% catalyst.
     

  8. KD8NPB
    Joined: Mar 2018
    Posts: 162
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    Location: South Carolina

    KD8NPB Senior Member

    Gelcoat should be applied and covered with 300g to 900g of fiberglass in less than 8 hours. Ideally within 4 hours of cure.

    Standard gelcoat is a 20-24 minute gel time (100g lab cup), which translates to cure at 90-120 min at 0.5mm / 25C.

    It should be reinforced once it no longer transfers to a gloved finger. It is recommended to put a fan blowing across it to aid removing styrene vapor during cure (which is heavier than air and will retard cure times).
     
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