Gelcoat Brands (one sticks, the other doesn't)

Discussion in 'Fiberglass and Composite Boat Building' started by itchyglass, Oct 20, 2023.

  1. itchyglass
    Joined: Aug 2022
    Posts: 34
    Likes: 2, Points: 8
    Location: MA

    itchyglass Junior Member

    Hi all, I thought this was interesting and really do not know why this happens. I tested two different brands of gelcoat on a brand new mold that was prepared using a sealer, and then wax applications. I have found the seafoam green brand of gel bonds easy to the mold where the white flakes off as usual.

    Any ideas? I did not expect to see such a difference in the brands. Maybe one has a different ingredient that happens to be incompatible with my preferred wax?
     

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  2. ondarvr
    Joined: Dec 2005
    Posts: 2,935
    Likes: 581, Points: 113, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    You'll need to explain "bonds easy to the mold" and "flakes off as usual". The pic doesn't tell the whole story.
     
  3. itchyglass
    Joined: Aug 2022
    Posts: 34
    Likes: 2, Points: 8
    Location: MA

    itchyglass Junior Member

    The seafoam green needs to be scrapped off with a brass paint scraper... even then it is hard to get off, chip by chip it can be "hammered" off. The white comes off as expected. Once a blade gets underneath an edge the entire patch of white gelcoat can be lifted off the surface.

    You can see a small patch of haze where the white gelcoat was. I am assuming this is from stryrene migration. I have not encountered this problem in previous molds. This particular mold is brand new. I went with a 2% catalyst ratio on the layup and post cured it at 90 degrees for 3 days. The past week it has been sitting at 73 degrees while I wax it up. (Only five coast so far... I usually aim for 7-8).
     
  4. ondarvr
    Joined: Dec 2005
    Posts: 2,935
    Likes: 581, Points: 113, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    It looks like the tooling gel coat isn't fully cured, or the mold isn't wax good enough.

    The difference in cure rate between the green and white can cause the difference between the two. The green is most likely a white tint base with green pigment added. Green pigments can have a big affect on the gel time, the longer the gel time, the more chance of it bonding to even a fully cured and prepped mold surface.
     

  5. itchyglass
    Joined: Aug 2022
    Posts: 34
    Likes: 2, Points: 8
    Location: MA

    itchyglass Junior Member

    Interesting. I did not know that about green pigments. I have used the exact seafoam green gelcoat in other molds of mine with no issues. It just seems to be really hard to use on brand new molds... I had a previous mold completely ruined by it. Hopefully after a few more wax and buffs I'll run another test with the white before spraying the entire mold.
     
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