Epoxy/paint questions

Discussion in 'Boatbuilding' started by Travis Grauel, Mar 31, 2020.

  1. Travis Grauel
    Joined: Jan 2020
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    Location: Maryland

    Travis Grauel Junior Member

    So I’m currently to the point of fiberglass and epoxying my boat...my current issue is how to Acheive a smoothish finish? I’ve put 1 layers of 7018 biaxal cloth and 2 separate coats of epoxy and have tons of rather large dips and belly’s in the epoxy even though my layup was bubble free? I thickened my last coat with silica and skimmed it on but I think that may have made it actually worse because the thickened epoxy didn’t self level... my next question is I know I will not achieve a perfect Finnish before paint so I was going to use a build up primer for any small imperfections and fairing compound where needed but what paint do you guys recommend for a boat that will be pulled in and out of the wate r when used and was a high gloss finish? I imagine standard topside paint will not suffice? Thanks !
     

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  2. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    How tall are the lumps?
    How thick is the layer of silicanized epoxy?

    Unfortunately, you probably did create more work for yourself. Silica not only thickens epoxy but also makes it harder to sand.

    I hate to advise without all the information. So my advice may change as I'm better informed.
    Suspect sanding down the Alps then fairing with a mostly MICRO-BALOON fairing mix. A bit of silica helps prevent sagging, but not too much that it impairs sanding.

    Don't be fooled into thinking hi-build primer works for fairing. It should not be applied in a thick enough for fairing. It works wonders at filling in scratches in the true fairing.

    The higher the gloss the more imperfections show up. Be prepared to spend some significant time long boarding
     
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  3. Travis Grauel
    Joined: Jan 2020
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    Travis Grauel Junior Member

    I would say from high to low spot at the biggest would probably be about an 1/8”. Would 2 or 3 thin hot coats of epoxy help smooth it out or would it just follow the imperfect surface? I’ve already used 6 gallons of epoxy up to this point on the hull alone...thanks!
     
  4. gonzo
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    gonzo Senior Member

    I would start by sanding using a grinder with a hard disc. My preference is to glue coarse grit floor sandpaper to a depressed center grinding wheel. Low strength spray adhesive is the best.
     
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  5. missinginaction
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    missinginaction Senior Member

    Well, it's not that big. I'd have a go at it with a random orbital sander. 1/8" is pretty uneven so maybe you can knock the high spots down. I've seen autobody guys shoot a thin coat of black paint (just pick up a cheap can at the hardware store) on an uneven surface. This is called a guide coat. Helps you see what you're doing. You'll sand the paint off the high spots quickly and it will remain in the low areas. Once you're close you could make yourself up a long board or fairing board and get it closer by hand. Maybe this old thread will help...

    Get hull surface even? https://www.boatdesign.net/threads/get-hull-surface-even.59424/

    As for the paint. Some people might disagree with me but if you're going to knock this one around and drag it on beaches I'd use a good two part linear polyurethane paint. Once it cures (these paints "react" like resins rather than dry) you'll have a very hard surface that's resistant to abrasion. I use Interlux Perfection on everything and I love it. I like the bright whites. Even if you bang the boat and get a ding or deep scratch the bright whites are easy to touch up. They tend to blind you in the sun so they are forgiving of little imperfections. They're a little pricy but you won't need tons of paint. I'd say two quarts would be more than enough to do the boat inside and out. Of course you'll need the recommended primer. Money well spent if you'd like to keep the boat for a few years.
     
  6. Travis Grauel
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    Travis Grauel Junior Member

    Thanks a ton ...would grey primer be no good if I was going to be putting multiple layers of whiteish color?
     
  7. Blueknarr
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    Blueknarr Senior Member

    How thick is the layer of thickened epoxy over the glass?
    How far apart are the peaks?
    Any color of aerosil paint will do. It is misted on and should be fully sanded off. graffiti-mist-speckles-in-black-over-white-vector-14149015.jpg
    What is your skill level using power tools? Agressive tools and grits are a double edged sword. In skilled hands they make quick work of lumps and bumps. However, a novice can quickly destroy a surface. I like long boarding by hand. Starting with agressive grits can remove the most agrevious issue surprising quickly while minimizing potential damage.

    What level of finished paint quality are you striving for?
    How much effort are you willing to put into it?
    What paint application techniques are available to you and at what proficiency?
     
  8. Travis Grauel
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    Travis Grauel Junior Member

    Lumps are probably inches apart scattered pretty randomly across the boat the thicker epoxy is maybe a 16” thick but total epoxy probably closer the an 1/8” over the glass....i think I’m going to try and spray paint on hull and try to knock down most of the high stuff... if I get it close to smooth with minimal small lumps do you think a layer or 2 of epoxy will help smooth it out to make even less sanding?? .I think I’m very handy with tools and am willing to put lots of work into it as I have up to this point...I’m looking for a nice smooth high gloss finish with a ice blue paint...I’m willing to come to the realization the paint won’t be FLAWLESS and I’m ok with that I will be using a spray gun for paint but will be my first time useing it..,I will be practicing before hand..I am looking at purchasing awlgrip 2 part urethane paint ...how many quarts do you think it will take to do this 18 foot hill only rather thick?? Thanks for the help big time!
     
  9. missinginaction
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    missinginaction Senior Member

    You're on the right track. Just be careful as you sand as you don't want to go through the top layer of the plywood. You may find that you don't need to coat the entire project with more resin. You may be able to get away with just a little filling in certain spots. Are you using foam rollers? I like the Wooster 1/8" nap solvent resistant foam rollers. You can get them from Amazon but may find faster shipping somewhere else. This corona thing has Amazon's shipping all messed up. Those rollers work great for the paint too.
    Awlgrip is similar to Perfection. A couple of quarts should do. You'll need the recommended primer as well. And a quart of solvent. Before you use a 2 part LPU read the instructions until you know them by memory. Follow the instructions exactly, to the letter. A lot of people hate LPU's. I've found two main reasons for this. They thin the paint too much trying to "stretch' it because it's a little expensive. The second reason is they apply too much paint and it runs. 2 part LPU's are thin but they cover well. When you're applying remember the expression "less is more". Better to apply three or four thin coats than try to do a couple of thick ones. You might want to mix up a small batch and do a practice run on a small vertical piece just to see how the paint behaves.

    Best,

    MIA
     
  10. Blueknarr
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    Blueknarr Senior Member

    An 1/8th of an inch of thickness is barely enough to fair. Wait to add any more epoxy until it is fairer and then only if it is needed. In my decades as a painter, I can't remember ever seeing a coat painted on smoothing anything, add problems from poor application. Each variance in epoxy will sand differently. Slicing through different epoxy compositions will become difficult to fair.

    Three common fairing mistakes:
    1 relying on power tools over longboards
    2 using coarse grits for too long
    3 starting with the fine grits too soon
     
  11. fallguy
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    fallguy Senior Member

    You need to longboard the boat.

     
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  12. fallguy
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    fallguy Senior Member

    We use carbon guide powder. We also found abranet in 40 grit which would work well at the very start of fairing. The 80 grit cuts pretty slowly. All we had for the pictures was the 80 grit. It didn't last too long cutting epoxy paint.

    It was amateur hour for about a month here.

    You can see we painted early. See the waviness?

    E9EF91D3-CE2B-444D-9A2B-533003A68356.jpeg

    Then attack with a longboard. Should have been done prior to paint. Even this board work wasn't that great; we needed to use the board at more of an angle. It must be noted that fairinf after paint also means you are cutting harder materials!
    CD0CAB06-25AA-473E-BCBC-1C2D5201F36E.jpeg
    3666ACA6-9DEE-4F88-92A3-926C70451159.jpeg
     
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  13. fallguy
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    fallguy Senior Member

    We measured the depths and the greatest depth we had was 0.015" or so.

    If you have 1/8 highs and lows; you use fillers.

    Here is a still pic of my friend applying fillers. He tended to fill incorrectly and too vertical and I did not stand on him enough. Filling is done best on an angle like 45 degrees. This reduces the fills and the subsequent sanding. CC821FA0-A7E8-4596-9A9E-2D0EDCC4CF84.jpeg
     
  14. Travis Grauel
    Joined: Jan 2020
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    Location: Maryland

    Travis Grauel Junior Member

    Wow thanks for the awesome feedback! The pics and video do help..I am making a longboard at the moment and will fill and try a start at 80 grit if that doesn’t work I’ll go down to 40... once it’s pretty smooth should I skim some thickened epoxy on the surface and sand that down with 120? I purchased a 24 inch skimming knive that should help with smoothing out the coats thanks !
     

  15. fallguy
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    fallguy Senior Member

    The skimming knife sux. Buy a 12-14" concrete trowel. The skimming knife will leave the fairing up too high, generally. Fairing compounds are much thicker and heavier than sheetrock compounds.
     
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