Sealing a plug

Discussion in 'Boatbuilding' started by sweetwater, Apr 26, 2010.

  1. sweetwater
    Joined: Feb 2009
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    Location: Destin, FL

    sweetwater Junior Member

    I've got a question for those with some experience making/fairing plugs. We're making a plug that has several skin coats of door skin/luan and using bondo and thickned epoxy resin to fair. Just recently with the increase in temp and humidity the exposed wood (wood that has been sanded down past the bondo and epoxy) has distorded a little. It's only obvious to the touch when running your hand over it quickly.

    My question is should I seal the whole plug with epoxy resin or something. Or maybe lay a layer of glass. I'm hesitant to lay glass because I feel that it will just add more work to cover the print through.

    I was planning on priming, then using duratec spray fair but I'm not sure if this will "seal" the absorbative qualities of the open wood grain. Anythoughts?

    I'm attaching a picture of the plug.
     

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  2. Lurvio
    Joined: Jul 2009
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    Lurvio Mad scientist

    Is the wood just coarse to the touch or has it shrunk or swelled?

    I haven't done molds like that, but I'd say if the wood hasn't gotten water on it, just recoat the whole thing with epoxy.
     
  3. sweetwater
    Joined: Feb 2009
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    sweetwater Junior Member

    The wood isn't necessarily course to the touch, it has just "warped/raised" where exposed. Just a few days ago this wasn't the case, the plug was almost fair. I assume that with an increase in moisture and the heat added through sanding caused the exposed wood to raise due to expansion.

    I'll probably end up just coating in epoxy.
     
  4. apex1

    apex1 Guest

    You MUST seal all open surface of the wooden structure (on the "backside" of the plug) it will "work" otherwise.

    Using simple exterior house paint in three layers should do the trick.


    Regards
    Richard
     
  5. sweetwater
    Joined: Feb 2009
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    sweetwater Junior Member

    By "backside" of the plug do you mean the exposed outer surface and the "internal" surfaces. I'm afraid it would be too late to coat the inside but the outside can and will be coated with something.

    Question with using exterior house paint. Should it be used with a primer so that the coatings bond to the wood and are not pulled away from the plug when pulling off the mold?
     
  6. apex1

    apex1 Guest

    God NO!

    Do NOT apply that paint on the surface of the mould!!!!

    You did already one mistake not to seal the inner sides of your plug (there the paint helps).
    The surface was sanded down into the wooden structure (that was another mistake), and should have been immediately sealed by Epoxy or whatever stuff you use for the coating.
    Leaving wood open on the backside of your "nice" surface will always end up in a distorted plug once the humidity changes.

    ALL the structure of the plug has to be sealed against humidity! So turn it and do that first, you otherwise have a never ending problem.

    Regards
    Richard
     
  7. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    Duratec is the name of the most commonly used plug surface preparation products I am aware of. Applied over whatever you have extablished, and done as directed, you will have a perfect surface to make your mould from.

    ...and yes, as Apex says, also protect the inside asap with some sort of cheap coating to protect the plug even though it will be destroyed very soon, any moisture entering the plug wil distort it, so a few litres of cheapo paint is money well worth spending.
     
  8. sweetwater
    Joined: Feb 2009
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    Location: Destin, FL

    sweetwater Junior Member

    You had me wondering as well with the house paint. I really couldn't comprehend applying house paint to the mould surface. Kind of caught me off guard. I now realize that by "backside" you meant surface inside the plug.
    I think we just had our verbage crossed.

    As I said, I am planning on re-coating in epoxy, realizing that I should have sealed immediately following the exposure of the ply.

    I guess my original question was how far should I take it. A layer of glass, then high-build, etc.. or just epoxy rolled on to seal then procede.
     
  9. apex1

    apex1 Guest

    Depends on how much stability you need to achieve, if glass fabric is recomended or not. Usually it is a waste of money, and additional labour to fair out the fabric pattern (print through).

    If your plug ist too flimsy to be turned over and sealed inside, it might be worth the effort. On the other hand, it will be cheaper I guess, just to stabilize the climate conditions until you have your mould made.
    If there (structurally) is no glassing needed, you are fine with Duratec as Lubs mentioned, and Ep would be overkill.

    Regards
    Richard
     

  10. sweetwater
    Joined: Feb 2009
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    Location: Destin, FL

    sweetwater Junior Member

    Thanks for the advice. We'll be covering with duratec.
     
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