Building a mold

Discussion in 'Boatbuilding' started by sailorboy31, Dec 7, 2009.

  1. sailorboy31
    Joined: Dec 2009
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    sailorboy31 New Member

    Hello
    I am trying to find some info on Pro's and Con's to building a mould using plaster, and do you need to lay down the gel-coat before laying up your epoxy?
    Thank so much!
    Casey
     
  2. apex1

    apex1 Guest

    It is very porous, but thats all. The brittleness can be handled by using old potatosacks as reinforcement. (might be a bit difficult to find them nowadays).

    You do NOT use gel-coat crap when using Epoxy!!!
    Just let the first layer of Ep. go gelled then lay up a very light fabric (less print through).
    Do the complete layup in one go, do´nt let the layers cure thoroughly before applying the next!!!
    Paint the hull with a UV blocker paint, otherwise your boat will disappear after a while.

    Regards
    Richard
     
  3. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    Not sure what you are trying to achieve,are you wanting to build the male plug or the female mold out of plaster? It is not uncommon to use a framework,lath,plaster,Burlap as Apex mentioned etc,whatever it takes to make the plug but make the female mold out of conventional moldmaking materials such as polyester tooling gelcoat,glass and polyester resin and some kind of supporting structure be it steel or wood depending on how big the mold and how many pulls you are expecting to do.You could use epoxy at greater expense but im not sure of any advantage,id save the epoxy for the actual product,i think you need to tell us what you want to make,mold or plug,what is the item you want to make,is this for a one off or production etc.
    Steve.
     
  4. wardd
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    wardd Senior Member

    years ago when i made plaster plugs and molds, we mixed sisal in the plaster then a layer of plaster slurry

    and as a parting coat we used simonize car wax, many coats
     
  5. SamSam
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    SamSam Senior Member

    I've made small 1 and 2 ft square molds of plaster and sealed them with cheap spray paint in a can. A coat or two of wax and some pva and they work good. They can capture an incredible amount of detail.

    Fiberglass window screen works good for reinforcement. For that matter, I've heard of window screen being used instead of glass in layups. I suppose metal window screen would add an interesting sort of strength to a "fiberglass" layup. Anyone ever tried it?
     
  6. apex1

    apex1 Guest

    What please is window screen Fiberglass???

    Do´nt let me die dumb please.
     
  7. wardd
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    wardd Senior Member

    window screen is a wire mesh to keep bugs out

    and the post was to add it to the fiberglass or instead of fiberglass

    i dont see the advantage unless fiberglass irritates you
     
  8. Landlubber
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    Landlubber Senior Member

    sailorboy,

    It would depend entirely on the number of items you wish to pull of the mould....or do you really mean the plug.

    The plug is the thing that makes the mould, though you can of course go direct, but that is rare for production work
     
  9. apex1

    apex1 Guest

    Wardd, I know what that is. But Sam said "Fiberglass window screen" and I have no clue!
     
  10. Howard N
    Joined: Apr 2008
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    Howard N New Member

    It's hard to find metal window screen in lots of places. Up here, what you find is made out of a plastic they call fiberglass.
     
  11. apex1

    apex1 Guest

    Thank you Howard!
     
  12. SamSam
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    SamSam Senior Member

    I've never used it but if resin stuck to it it might offer some structural goodies like light weight, flexible, stretchable, who knows what else. Sort of cheap also.


    [​IMG]
     
  13. sailorboy31
    Joined: Dec 2009
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    sailorboy31 New Member

    Thanks everyone for the responses
    We are going to attempt to build 3, KHD 19 foot Trimarans, and at first we were just going to cold mold them, then there was a suggestion made about using plaster and forming a female mold then laying the glass up in side the mold and popping the shell out and lay in the bulk heads and stringers in afterwards. What do you think of this idea?

    Thanks so much!
    Casey








     
  14. SamSam
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    SamSam Senior Member

    If the shape is something a sheet of ply can conform to, there are cheap sheet materials that will work. It's hard to fair a female mold with materials like plaster.

    It's way better to put the bulkheads and structure in while the shell is in the mold where it is supported in the correct shape. Once you take it out it is usually too flimsy to keep the shape.
     

  15. PAR
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    PAR Yacht Designer/Builder

    Richard, you can get aluminum, steel, painted steel, galvanized steel and stainless steel (really hard to find), bug screen in this country. The 'glass materials are easily the most common now, but only in the last few decades. The metals are still used in tougher environments, like animal enclosures. Elongation issues would cause problems if used in a resin matrix for most marine applications. The coated screens would have peel strength issues as would the aluminum, unless etched just as you applied the resin.
     
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