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Thread: Fairing and Paint question

  1. #1
    Join Date
    Sep 2015
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    Ellsworth, ME
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    Default Fairing and Paint question

    It's April vacation, so my 13 yo daughter and I are back working on her Candlefish 16. We've filled the weave today with a 2nd coat of epoxy, and we'll be fairing tomorrow. Tried to get QuikFair at Hamilton, but they were out, so I got Microlight Filler (410) instead.

    After sanding the 410, can we prime with Multi-Marine Primer (Epifanes), and skip any epoxy seal coat? Seems like another epoxy coat would make the surface rough again.

    We'll be top-coating with Epifanes Polyurethane topside paint (above waterline), and Aquaguard bottom paint (directly on the epoxy) below the waterline.

    Thanks, Nate

  2. #2
    Join Date
    Oct 2010
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    Central Vermont
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    219

    Default Re: Fairing and Paint question

    The guidance from West is that you must put a layer of epoxy on top of 410 Filler. If I recall correctly, there was a concern that the 410 could compromise the finish of the paint if that wasn't done.

    However, the guidance for 407 Filler doesn't require a layer on top of it, but says something to the effect that it could be done.

    407 is less fine than 410, and is more difficult to sand, but, if you really want to save the epoxy layer step, maybe you could take your 410 back and exchange it for 407.

  3. #3
    Join Date
    Jun 2000
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    Madison Wisconsin
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    Default Re: Fairing and Paint question

    Any filler using microballoons (including 407) should ideally be resin top-coated for best results. The reason is that sanding microballoon fillers fair tends to cut open some of the hollow balloons at the surface. The following coating (resin, paint, etc.) won't fill these tiny hollow spaces. It will bridge them. When the bridge is just paint it can heat up from the sun, expand the air inside and pop the bridge, leaving a tiny but visible pinhole in your paint job. A resin sealer coat is generally strong enough to make bridges that won't pop. I've even seen two-tone paint jobs where one color ended up pin-holed all over and the other color had more pigment, thickness or film strength and the bridges held up. The strange thing was that the color that pin-holed was white. The color that didn't was dark green, which you would think would have heated up a lot more in the sun. I don't know whether or not your primer is strong or thick enough to skip the sealer coat of epoxy, but those are the principles at play. An epoxy top coat does need sanding if you want a nice surface to paint on that won't show as lumpy through your paint, though it goes pretty quickly.

  4. #4

    Default Re: Fairing and Paint question

    That is why I no longer use microballoons. Sure, they result in a fairing that is a little bit easier to sand. But they require an extra session of epoxy coating and an extra session of sanding. Omitting microballoons results in a fairing that is a bit harder to sand but eliminates the added session of epoxy coating and the added session of sanding.

  5. #5
    Join Date
    Nov 2010
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    Wellington, NZ
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    Default Re: Fairing and Paint question

    I was advised by someone more experienced than me that the 410 leaves a soft surface, so the epoxy topcoat hardens the surface as well as sealing all the popped balloons.

  6. #6
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    Default Re: Fairing and Paint question

    Yes, it's pretty soft. Sometimes there is another advantage to the epoxy top-coating that can make the additional sanding job worth the trouble. If your fairing job turned out a fair shape, but one which shows patches of filler in some spots, and patches with no filler in other places they may or may not finish up looking the same under your paint. It's as if your paint sits nicely in some spots, but looks like it has a different texture in the filled areas, giving the entire paint job a rather blotchy look. A consistent and sanded epoxy top coat eliminates this, as well as making a base coat to paint on which is often better than the vast majority of primers - usually making them unnecessary. If I can have my paint sitting on a tough, extremely moisture and abrasion resistant, evenly sanded epoxy surface, or on a primer which is formulated to sand off easily, I'll put in the extra effort and choose the epoxy every time.

  7. #7
    Join Date
    Dec 2003
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    Portland, Oregon
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    40,234

    Default Re: Fairing and Paint question

    Quote Originally Posted by Todd Bradshaw View Post
    Yes, it's pretty soft. Sometimes there is another advantage to the epoxy top-coating that can make the additional sanding job worth the trouble. If your fairing job turned out a fair shape, but one which shows patches of filler in some spots, and patches with no filler in other places they may or may not finish up looking the same under your paint. It's as if your paint sits nicely in some spots, but looks like it has a different texture in the filled areas, giving the entire paint job a rather blotchy look. A consistent and sanded epoxy top coat eliminates this, as well as making a base coat to paint on which is often better than the vast majority of primers - usually making them unnecessary. If I can have my paint sitting on a tough, extremely moisture and abrasion resistant, evenly sanded epoxy surface, or on a primer which is formulated to sand off easily, I'll put in the extra effort and choose the epoxy every time.
    Horses for courses, and budgets do come into play (both time and $$). But in general, I concur. As with much about finishing - the prep work is a case of, 'pay me now... or pay me (slightly, or tons) more later.
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  8. #8
    Join Date
    Dec 2009
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    Default Re: Fairing and Paint question

    I use both 407 and 410 West fillers. I find 407 better for filling the weave and the colour is helpful when you want to sand down to face of cloth. I like a 6" drywallers knife for the majority of my epoxy applications and would use it for a skim coat application over the sanded filler, assuming you are working down. Complete your fairing before you get to this stage.

    The 410 will be fine for your application: it might scratch a little easier than 407 but you have the technology to repair that. Good luck with your paint job! / Jim

  9. #9
    Join Date
    Nov 2016
    Location
    Nokesville, VA, USA
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    42

    Default Re: Fairing and Paint question

    I have not worked with this specific product, but I have done a lot of "filling." Generally speaking, fillers are some sort of pigment or dust that get shoved into voids to make a smooth surface. In this case, it sounds like the filler is microbaloons. Whatever the substance is, it needs something to hold it in place. Otherwise, it'll come right back out. If the product instructions say to apply another coat of epoxy, I'd take their advice. It sounds like it doesn't have enough sticky stuff already in it to keep the microbaloons in place. I'd be worried about adhesion problems with the primer.

  10. #10
    Join Date
    Jun 2000
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    Madison Wisconsin
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    Default Re: Fairing and Paint question

    If all I'm filling is cloth weave, I just use plain epoxy. It's a lot tougher than something like 407, 410 or any other balloon-based substance, and it eliminates any surface with dissimilar materials exposed. The rule of thumb is to apply thin filler coats, rapid-fire, as soon as the previous one is stiff enough that you won't disturb it and to apply enough coats to completely hide the weave - plus one more as a sanding cushion. Assuming that the surface you glassed was fair (which it should have been before glassing) sanding the final filler coat smooth is pretty quick and easy. Give it a week to fully cure (health hazard if you don't) and a $50 random orbit sander will make it baby butt smooth. I don't understand why so many people are afraid of sanding epoxy unless it's been dramatically softened with a lot of filler powders. Plain resin actually sands pretty well, and you can finish sand a small-to medium-sized boat in a couple of hours with 80 grit, followed by something in the 120 grit range and be smooth and ready to paint or varnish.

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