Plug mold

Discussion in 'Fiberglass and Composite Boat Building' started by LowelandSystem, Mar 22, 2016.

  1. LowelandSystem
    Joined: Nov 2015
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    LowelandSystem Junior Member

    Hello good fellas,
    I am really fighting with wood plug mold. I have finished the design, but how to give it a surface A gloss finish, is it normal enamel paint with varnish, or procedure same as car painting, please help me with this... TIA
     
  2. jorgepease
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    jorgepease Senior Member

    Most of the time Gelcoat and then sanded and polished
     
  3. gonzo
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    gonzo Senior Member

    The styrene in the resin will dissolve and lift the enamel or varnish. You need gelcoat or a urethane or polyurethane with hardener.
     
  4. steve123
    Joined: Dec 2014
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    steve123 Junior Member

    Durabuild is what you need for plug, its easy to sand then wet 'n' dry finish before polishing.
     
  5. LowelandSystem
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    LowelandSystem Junior Member

    Guys is there any alternative method, beside, will the mother mold will be in fiberglass too, I made a mother mold in sheet metal, worked preTTy well, but not much detailing I put it into. :(
     
  6. jorgepease
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    jorgepease Senior Member

    Gelcoat is pretty easy and not expensive, why do you want another method?
     
  7. LowelandSystem
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    LowelandSystem Junior Member

    I put a gelcoat in a mold, it is still sticky after 3 weeks
     
  8. gonzo
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    gonzo Senior Member

    It is air inhibited. You need to add wax to it.
     
  9. steve123
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    steve123 Junior Member

    If you put gelcoat in a mold that's the gelcoat for your molding, if that's the case you certainly do not want wax in it.
    The resin and glass will not adhere to waxed gelcoat, the mold is obviously waxed prior to applying your first gel, usually you require a fan blowing into the hull after gelcoat to remove styrene fumes. Slight tacky feel to gelcoat is normal before applying first layer which should be applied within 24 hours max.
     
  10. LowelandSystem
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    LowelandSystem Junior Member

    Thanks a lot, that will help so much.. :)
     
  11. Jamie Kennedy
    Joined: Jun 2015
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    Jamie Kennedy Senior Member

    What Gonzo is refering to is that gelcoat will not cure when exposed to air. When using a mold to make a boat, this doesn't matter, because it have the waxed mold on one side, and the rest of the layup on the other side, and so it will fully cure as it is not exposed to air.

    However, when you make the mold, and you spray that with gelcoat, it will not cure because it is exposed to air on one side. So you need to add this stuff called 'mold release agent'. I think this is some sort of a wax, or alcohol, or both, that finds its way to the exposed surface, and thus forms an air barrier and allows the gelcoat to fully cure. I think you can also spray something like polyvinyl alcohol over the gelcoat after spraying on the gelcoat. not sure which is better as I haven't done either. My brother does this stuff. I just fix boats.

    Once the gelcoat surface has hardened you still need to wax the mold before you use it, but that is a separate thing. steve123 is correct that you don't want to add mold release agent to the gelcoat of your finished product, and not just because you don't have to, but that is not what Gonzo was talking about. Gonzo was talking about gelcoat for coating a mold, or anytime you want gelcoat to fully cure, and not just gel, while exposed to air.
     
  12. jorgepease
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    jorgepease Senior Member

    Try painting another layer of gelcoat on with the wax additive and it should harden fast.
     

  13. SamSam
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    SamSam Senior Member

    I've used auto enamel and spray can enamel to finish plugs, followed by multiple coats of 'mold release agent' and one coat of PVA and had no problem. There are better things to use though, if they are available.

    http://www.fibreglast.com/

    If you want gelcoat and polyester resin to cure so it's not sticky, you block the air from the surface with a RESIN ADDITIVE consisting of paraffin wax dissolved in styrene ( http://www.fibreglast.com/product/Styrene_Wax_71/Resin_Additives ) or you can spray the surface with PVA ( http://www.fibreglast.com/product/PVA_Release_Film_13/Mold_Releases ) or you can cover the surface with plastic, such as when vacuum bagging or infusing.

    If you need to do more laminations on the surface, you need to remove the wax, or remove the PVA. With plastic there is no residue to remove, (except of course the plastic) but with all three methods you probably have to rough up the surface with sanding, etc. and you achieve at best a secondary bond. Removing wax is difficult so you get a crappy secondary bond, PVA is water soluble so you get a better bond.

    If you leave out or off the air blocks, (wax-PVA-plastic), the surface remains tacky and subsequent laminations, if done soon enough) will have a much better and deeper chemical/primary bond and be stronger than the secondary bond.

    It is much easier to work on a convex surface (outside of a bowl) as compared to a concave surface (inside of a bowl).

    When you make a plug, you want to get the finest surface you can get, ideally you get it as smooth and shiny and polished as the finished product is going to be. If the plug will have convex and concave areas, the convex areas should be finished to perfection. The concave areas should be finished as much as possible. When the mold is made, those concave areas will become convex and can be finished to perfection on the mold itself.

    So, when making the mold from the plug, the first step (after waxing and PVAing the plug) is to coat the plug with UNWAXED TOOLING gelcoat ( http://www.fibreglast.com/product/Orange_Tooling_Gel_Coat_just_gel_coats_188/Polyester_Resins ). After that is set, the rest of the laminations will be applied using UNWAXED LAMINATING resin ( http://www.fibreglast.com/product/Polyester_Molding_Resin_just_resin_77/Polyester_Resins ) so each layer will have a primary bond to the previous one. The last layer of the mold can use waxed resin, PVA, plastic to end up non-sticky, or unwaxed resin can be used and the outside of the mold painted. Latex paint works fine.

    When you take the mold off the plug, it is pretty much ready to go, maybe needing some light buffing and polishing.

    To get a part from the mold is pretty much the same process.
     
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