mold materials?

Discussion in 'Materials' started by kapnD, Nov 1, 2003.

  1. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Will surfaced particle board work as a one-time use mold? Am adding to the length of fiberglass boat, plan to cut off entire boat in straight section near transom and stretch it out 3' by screwing surfaced particle board (the kind they use for cabinet interiors) across the gap and glassing over it from the inside. I believe the surface of the particle board is vinyl. Is this compatible with PVA, or since its already vinyl, could gel coat be applied directly to it? Also will vinyl tape (package wrapping tape) be ok to use over the joints? Since this is a one-off deal, I'm not looking for a perfect finish, just a quick and effective mold.
    any thoughts/input appreciated!
     
  2. slneatboat
    Joined: Nov 2003
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    Location: Norfolk,England

    slneatboat Junior Member

    Gellcoat should release of this board but i would use pva just to play safe and it will be so much easier to release when finished,as for the tape i would use either masking tape or cellotape.This may seem obviouse but pva last after the mould has been screwed to the boat and taped up so it dosen't get rubbed or scatched off.Hope this helps.
     
  3. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    layup question

    slneatboat, thanks for the input on the mold matls, now wondering about the joint between new and old. All the overlap will necessarily be on the inside so after removing the mold, will I need to grind out the joint on the outside and glass over it there too?
     
  4. slneatboat
    Joined: Nov 2003
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    Location: Norfolk,England

    slneatboat Junior Member

    If you grind a tapered edge on the inside of your boat before you start say 4 + inches,then when you srew on the mould the join between boat and mould should pull up tight with no gap,so when its gelled and layed up it becomes one,so when the mould is taken off hopefully there should only be a small ridge which only needs rubbing down with sand paper or wet and dry,so no you don,t need to grind and bond the outside,the bond is on the inside.The inside taper you have created is so the layers of glass can be made bigger and bigger so there won't be such a big overlap on the inside.
    Two exta points, i would key up with a grinder perhaps 12-18 inches on the inside of the boat and make sure some of the layers of glass bonds over this ,if you have to screw near the edges to close up the gap don't worry once a substantial number of the layers of glass have gone hard take the screws out put some gell in the holes (from the inside)then carry on laying up,dont bang, jump around too much because the mould may start to release.
     
  5. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Thanks again for the valuable input, especially what to do with the screws!
    Another layup question: Although the hull is white, I've read that layup is much easier over black. If I apply white, then black, is there going to be any bonding problem between the gelcoat layers? Will this be too thick a gelcoat layer? Is it worth the cost/effort?
    Mahalo Nui Loa!
     

  6. slneatboat
    Joined: Nov 2003
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    Location: Norfolk,England

    slneatboat Junior Member

    DON'T DO THAT ! ! !

    The black will show through the white.It could be said laying up on black shows up the air more when laying up but,your'e boat is white!.Apply two coats of white gellcoat ,there is no problem with the bond between the two, the second gell should be applied when the first one is tacky but leaves no residue on youre finger,the same is said on the second one as to when to start to lay up.The gellcoat should remain tacky on the lay up side. (However i believe the USA has tighter limits on the use of styrene in gell and resin than the UK so it may have wax or some other additive in for this not to be the case, check with supplier)One other point lay up using clear resin so you can see the air that has got to be removed,you can always do the last couple of layers in a colour if you want to make it look nicer on the inside of the boat otherwise don't worry.
     
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