Plywood mould fairing and finishing......

Discussion in 'Boatbuilding' started by wind_apparent, Oct 31, 2008.

  1. wind_apparent
    Joined: Apr 2008
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    Location: boulder colorado

    wind_apparent wind driven speed addict

    #1 Hi, I'm putting the ply skin on a mould I'm building for a sailing hydrofoil project I have going on. After the ply is on I will need to fill the holes and add material to the flat spots in preparation for fairing. Right now I see two options. Bondo , which fills quickly, is cheap, and fairs easily, and Epoxy/microlight, which is more expensive, harder to sand, but is much more durable. I'm not sure how many pulls I'm going to take off this mould, may be as few as one, but I hope more. As far as the Epoxy/microlight option, I'm building this mould in a space I have at work, so sometimes I won't have access to it for 3-4 days, will I be able to add more filler after that length of time and still have it stick?

    #2 I'm going to need to put some sort of mould finish over this, what would be a good, easy thing to do. Gelcoat? Sandable primer? Mylar packing tape? Any idea's? (If anyone has used the Mylar tape deal, I would like to hear what your experience was like. I would maybe like to use this for the first pull, then if I like the shape and want to make more hulls I can finish out the mould proper like without sinking any money into it till I know it's worth it.

    If your adding a suggestion, please include the process so I know everything I'm getting into to do it that way.



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  2. keith66
    Joined: Sep 2007
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    Location: Essex UK

    keith66 Senior Member

    I would use body filler (bondo?) in the corners or for filling screw holes followed by Durabuild, this is a grey polyester primer that can be painted on, or sprayed on. It cures fast, is easy to sand and can take a high polish, excellent stuff for mold or pattern making.
  3. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    For a low-temperature mould, Bondo is just fine. I've used it (well, 3M's version) for patching and fairing MDF plugs before taking high-temp moulds from them. What we did there was to fill the holes and divots in the MDF with Bondo, and sand the thing smooth. Alternating steps of fine sanding and coating with shellac left us with a smooth, tight surface that was then heavily waxed and polished. We took the hi-temp glass moulds (for autoclave use) from that. Although the plugs were only meant to be one-use,they survived just fine and we could have pulled another one or two moulds easily. (De-waxing the final mould was a pain, though.)

    A sandable primer would probably be a better bet; it would make it a lot easier to see flaws in the mould/plug. I'm a fan of Adtech ES-225 for this; it is, however, an expensive hi-temp system and, while sandable, is not exactly easy to sand.

  4. wind_apparent
    Joined: Apr 2008
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    Location: boulder colorado

    wind_apparent wind driven speed addict

    So, I've been looking onto it, I'm thinking epoxy/qcells as a filler/fairing compound then covering that with Durabuild sandable primer, sand and polish then vacuum bag to that, will this work well?
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