Hi build primer over FG laminate

Discussion in 'Fiberglass and Composite Boat Building' started by burke, Mar 15, 2017.

  1. burke
    Joined: May 2014
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    burke Junior Member

    I have finished applying and sanding poly fairing compound applications to the final FG cloth surface of a crowned composite roof panel. It's close but not ready to paint. Who can recommend a high build, non-resin based primer. After applying and sanding several coats I will apply an exterior acrylic enamel.

    I'm aware of Petit 6149. Pricey.

    Thanks
     
  2. ondarvr
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    ondarvr Senior Member

  3. burke
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    burke Junior Member

    I think you're talking about high build polyester resin based primer/surfacers. Like the one you referenced. I'm looking for a paint type high build likely alkyd primer, like Petit 6149.

    Thanks
     
  4. ondarvr
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    ondarvr Senior Member

    If you are looking for an actual high build product to hide all the nasty's and fair the surface, you need something that will build up more than just a few mils per application. The polyester products can be built up in 20-30 mil layers, and much thicker if needed to get the surface looking good. They also tend to be more durable.

    This is a real high build product.

    http://duratec1.com/pdf/DS 707-051.pdf


    When I said they're all resin based, it means even typical "paints" are resin based, just a different type of resin.
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    This is correct, inasmuch as all paints are resin based, though there are various types. If you're going to use an acrylic top coat, why bother with anything other than an acrylic primer?

    I like to seal down fairing compounds with a tough primer and the usual choice is an epoxy base. These sand easily initially, but become quite hard after a few days, so get your sanding done in this time frame. There are also waterborne epoxy primers now and System Three has one that's not too bad (cost). It dries hard, but with the same precautions as the other epoxies (sand it within a few days).
     
  6. burke
    Joined: May 2014
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    burke Junior Member

    Thanks all.

    I am looking at non-poly/epoxy resin based primer/surfacers due to the time constraints on post sanding. I want to prepare the panel for paint first. Later I will be butt joining this panel into the existing roof, requiring more glassing, fairing compound and sanding at the join. Don't want to face a product which will be hard/impossible to hand sand.

    At this point I just want to gain experience with high build, above waterline paint-type primers. I want to see if they coat/incapsulate any unseen FG hairs well enough. For this and other projects.

    And yes, a water-based high build primer would be fine. I don't know of any.

    Thanks
     
  7. jorgepease
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    jorgepease Senior Member

    If I am understanding right, I don't think you will save any time doing it that way. Especially if your join goes proud of the primer. How do you butt join without taping anyway, just adhesive?
     
  8. ondarvr
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    ondarvr Senior Member

    There are no time constraints on sanding these products, plus they will be 100% compatible with whatever you do in the future, paint type primers aren't. I'm not saying paint primers can't be used, they just have a narrower window of uses due to methods and products used with them.
     
  9. burke
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    burke Junior Member

    No, I'm not just butt gluing it together. Grinding the 12 to 1 taper, fabric, resin, fairing compound. On top and bottom laminates. The pre-finishing and priming of the new panel will stop within a few inches of the areas where I will tape. I'm pre-finishing most of the 3 by 7' panel as it's much easier to do it in my basement than in colder weather on the boat with a winter cover close to the work.

    Understand your last point if I use paint-type primer, I can't gelcoat ever in the future. It's something I had to consider before deciding. I appreciate very much the advice- but I want try a high build primer and see its value and limitations for future work.

    FYI, the manufacturer of one of the poly fairing compounds advised, hand sand within 2-4 hours and if you wait 1-2 days, it will be too hard to hand sand. They probably wouldn't want me to say their name online- I'll just say it's one of the major 4 companies who distribute polyester fairing compounds. I'm using Merton's Poly-Fair now and it's very easy to apply and easy to sand, at any time.
     
  10. Sparky568
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    Sparky568 Junior Member

    A former boat builder in Maine advised me to keep the poly fair to less that 1/4" thick. He had it crack on a few boats after a year.
     
  11. ondarvr
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    ondarvr Senior Member

    Polly Fair is not what we're talking about, and is a very different product compared to the high build sanding primers that are being discussed.
     
  12. SukiSolo
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    SukiSolo Senior Member

    Polyester 2K primers/hi build are fine to sand - the key is in the timing. To savea lot of work start cutting preferably wet as soon as the paint has cured enough. this is often a few hours only as it will continue to harden. If you leave it a day, your work wil take a lot longer...
     

  13. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Yes, you buddy is correct, you don't want heavy thicknesses of putty on a surface and 1/4" is about as thick as you dare, preferably an 1/8th is better.
     
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