New Gelcoat on a 1970 boat. Strange Yellow ring

Discussion in 'Materials' started by 500Lonepine, Jun 12, 2015.

  1. 500Lonepine
    Joined: Sep 2013
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    Location: Lake Leelanau Mi

    500Lonepine Junior Member

    I did a fiberglass repair on a 1970 sailboat. I purchased Westbay Marine Finish Gelcoat. I carefully mixed and matched the color. After application the edges of the Gelcoat turned a distinct yellow.

    Anyone have a thought on why this is happening?

  2. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Several things come into play.

    Did you thin the gel coat with something?

    Catalyst ratio?

    What colors did you tint the gel coat with?

    Were the pigments designed for gel coat?

    How much pigment did you add?
  3. Jamie Kennedy
    Joined: Jun 2015
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    Location: Saint John New Brunswick

    Jamie Kennedy Senior Member

    I was curious about this also. I think ondarvr is on the right track. I also wonder if it cooked off a little hotter is some spots than others, and if that can effect colour.
  4. SprayAway
    Joined: Jul 2015
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    Location: Manchester, UK

    SprayAway New Member

    Hi there' I repair GRP and FRP hulls often,
    It looks to me like tannin bleed.
    If the solvent is reacting to the hull, could it be that its seen paint before?

    Ive seen this before, where ive used 2 pack products on top of hulls that people think were 'original GRP'.
    When in fact, theyve seen paint before. Usually during drying you get this colour as above.

    May i suggest you bop a sander over the area, use a 1 pack vinyl primer, followed by an oil based paint topcoat to match..

    Hope that helps :)
  5. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    You may be right about the paint, although most 2k systems are pretty stable once cured. I've run into (and done) lots of repairs and it is hard to tell sometimes if they are post sprayed or proper gelcoat. Sometimes 2 or 3 times on the same hull!!.
    A one pack may well be more reactive however.

  6. SprayAway
    Joined: Jul 2015
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    Location: Manchester, UK

    SprayAway New Member

    Okay, 1 pack vinyl primer is ph neutral and doesnt react to anything. Its a sealant. It blocks out the underneath.
    If you put it on thick its a great primer with loads of adhesion.
    Vinyguard silvergrey is one id single out as top notch.

    Using a top coat like Pilot 2 over the top with a xylene based thinner will also be productive as it doesnt react with oil or grease.

    If youre using 2k you better make sure its on a bareboat.
    Ive had great work done on many yachts with 2k but usually you have to strip every bit of paint from the hull before considering it.

    Ive also had issues where ive declined work because people have asked me to paint 2k over existing paintwork.

    Those people generally come back 2 months later as the solvents in the catalysts eat away at the oils when at sea.
    They just dont understand the complexity of ph scales with water proof paints.
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