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Thread: Plywood hull fairing .......

  1. #1
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    Default Plywood hull fairing .......

    Newbie here building a small catboat. I've taped the outside seams and put down a first coat of fairing compound. The hull feels smooth but I know it isn't fair yet. I've convinced myself I don't want a yacht finish but don't want the hull rippled either.

    The more I research, the more confused I am. Way too many brands and types of compounds and finish techniques.

    i would like to color the hull to help make the uneven areas stand out and then decide whether to fair more or call it good and lay the cloth. So far I've found Easy poxy white primer and West 501 white pigment additive.

    Can I put more fairing compound on top of primer if it needs it?
    Attached Images Attached Images

  2. #2
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    Default Re: Plywood hull fairing .......

    Lay the cloth. Then get back to the fairing compounds. My favorite is West System 410 Microlight. But as you've seen, there are many ways to skin this cat. (So to speak.)
    -Dave

  3. #3
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    Default Re: Plywood hull fairing .......

    be sue to fill any obvious voids, and grind off any bumps or grungle before laying cloth.

  4. #4
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    Default Re: Plywood hull fairing .......

    Well, it takes forever.

    I recently did a boat with chines (I know) that has two layers of tape and two layers of cloth over the seams.

    A longboard helps a lot.

    Lightly pigmenting successive layers of filler helps. Or coloring one layer, and not the next, etc. Get the shape as close as perfect before glassing.

    Once the glass is on, and you can prime it, then the REAL fairing will begin. My favorite method is to lightly mist the area to be faired with red spray paint. Very thinly, sparsely applied drops of color will show the contours of the white substrate excellently.

    What kind of boat is that, anywho?

    Peace,
    Robert

  5. #5
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    Default Re: Plywood hull fairing .......

    "Easy Poxy white primer"...what is that? Is it a one part alkyd undercoater?

    I have not heard of it and cannot find it with google. If its a one part coating, its a big mistake to use it under the cloth.
    Do the pre glass fairing by feel, not so much by eye.(therefor, tinting the product to spot imperfections is may be overkill in your case). Fairing is not the same as smoothing.
    Round the chines a bit. Sharpen them up after the glass if you want em sharp.
    Stay with epoxy . Use 407 or 410 fillers . They are both made for easy sanding.
    What flavor of sander do you have available?
    bruce

  6. #6
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    Default Re: Plywood hull fairing .......

    I don't see any mention that there will be cloth going over the hull,nor do I see any reason for adding any.Thousands of ply dinghies have been built without a glass sheathing.If the concern is about fairing the additional thickness of the glass tape into the ply panels,it looks as though some of the work has been done.Its a lot easier btw to chamfer the last inch and a half down by a fraction before taping,but its too late for that now.The advice to stay with epoxy is good as it sticks to itself very well.A fairing batten will be a very handy thing to have as you can hold it in contact with the surface to show the low spots.Screed your fairing mix over the low spots and in due course sand the knobbly bits off and check again.Repeat as necessary.Even a high build paint won't fill huge trenches,so don't be tempted to skip a bit of fairing.Good luck.

  7. #7
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    Default Re: Plywood hull fairing .......

    " whether to fair more or call it good and lay the cloth. "

  8. #8
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    Default Re: Plywood hull fairing .......

    I hadn't seen that part and was going on the fairing compound by the tape,which I wouldn't have bothered with as I would have been keen to get the cloth the designer specified attached at a time that gives a good bond.Fairing a glass sheathed object is my least favourite boat related task by a long way.

  9. #9
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    Default Re: Plywood hull fairing .......

    Not sure which petit primer you are using but their single parts have always been oil based. You do not want to put any type of resin over an oil based primer. Otherwise I'd use a flexible sanding block at 45 degrees each way to fair the hull. Your eyeballs and lighting will be fine. If you are hexx bent on primers or fairing compounds now is the time to use them. If glassing make sure the covering is compatible with the undercoating/fairing compound.

  10. #10
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    Default Re: Plywood hull fairing .......

    Fairing is the process of removing highs and/or filling lows.
    It starts with the lofting.
    Continues with the framing.
    And is done on the planking unless... it is plywood.
    You can't removes highs on plywood for obvious veneer concerns.
    So half of the process is taken away.
    The fabric/resin sheathing adheres better to bare wood.
    Even after the planking is "glassed" you can't (shouldn't) sand into the fabric.
    Fairing compounds adhere well to resin after proper preparation.
    So, sheath/glass first then fair by filling the lows.
    You will get a good "feel" of how fair it is after a couple of 'filling and fairing' sessions and decide what is good enough.
    At least that has been my experience, anyway.

  11. #11
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    Default Re: Plywood hull fairing .......

    You will get a good "feel" of how fair it is after a couple of 'filling and fairing' sessions and decide what is good enough.
    At least that has been my experience, anyway.
    Yes, your hand is much more sensitive than your eye in the business of fairing.
    Steve Martinsen

  12. #12
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    Default Re: Plywood hull fairing .......

    The feel, yes, plus pigment in the resin and lighting from an acute angle.
    -Dave

  13. #13
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    Default Re: Plywood hull fairing .......

    Thanks for all the valuable input everyone. I tapered the tape before the first layer of fairing compound to smooth the tape edges. No obvious bad spots so I'll lay the glass and go from there. Really appreciate people who take the time to help out. I'll update once the glass goes on.

  14. #14
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    Default Re: Plywood hull fairing .......

    Quote Originally Posted by SMARTINSEN View Post
    Yes, your hand is much more sensitive than your eye in the business of fairing.
    I respectively disagree. Holding a light up will cast shadows that are seen but not felt by hand. Example: In the frp mold plug making business, machining dye diluted in water is brushed on to show high/low spots when sanding...faster, cleaner, thinner than any other coating and doesn't clog sandpaper as fast. This method produces results far beyond feeling. I'm not saying you can't get a good surface from feel but feel isn't in the same league as eye and dye.

  15. #15
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    Default Re: Plywood hull fairing .......

    As you proceed, I recommend you avail yourself of the authoritative - and free - downloads from West System -- https://www.westsystem.com/instruction-2/

    Or... you can get advice from us internet geniuses - whose expertise ranges from... 'been doing it professionally for years' to... 'did something similar on my boat once' to... 'read a magazine article a few years back' to... 'has never picked up a tool but has some thoughts'.

    Last edited by David G; 08-10-2018 at 11:37 AM.
    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)

  16. #16
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    Default Re: Plywood hull fairing .......

    As fairing progresses, the appeal of low-gloss paint becomes more apparent.

  17. #17
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    Default Re: Plywood hull fairing .......


  18. #18
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    Default Re: Plywood hull fairing .......

    C64C822D-CDDA-4A19-B992-699634316003.jpg
    Tell me about it...

    Peace,
    Robert

  19. #19
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    Default Re: Plywood hull fairing .......

    Quote Originally Posted by David G View Post
    As you proceed, I recommend you avail yourself of the authoritative - and free - downloads from West System -- https://www.westsystem.com/instruction-2/

    Or... you can get advice from us internet geniuses - whose expertise ranges from... 'been doing it professionally for years' to... 'did something similar on my boat once' to... 'read a magazine article a few years back' to... 'has never picked up a tool but has some thoughts'.

    Very apposite post.There is another forum I occasionally visit related to a hobby activity and one of the frequent posters has a signature line that implies he is a professional.Yet from the amount of time he spends posting and the times at which he does it,it is quite apparent that he isn't doing much.

  20. #20
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    Default Re: Plywood hull fairing .......

    Quote Originally Posted by John Meachen View Post
    Very apposite post.There is another forum I occasionally visit related to a hobby activity and one of the frequent posters has a signature line that implies he is a professional.Yet from the amount of time he spends posting and the times at which he does it,it is quite apparent that he isn't doing much.
    I resemble that remark

  21. #21
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    Default Re: Plywood hull fairing .......

    My weapon of choice is a cabinet scraper. Sanding surfaces with changing densities like fiberglass and wood or pronounced grain can create an uneven surface. A sharp scraper doesn’t care.

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