Final layer of mold plug?

Discussion in 'Fiberglass and Composite Boat Building' started by aaronhl, Aug 9, 2015.

  1. aaronhl
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    aaronhl Senior Member

    I used a layer of spray paint sanding compound over epoxy on the mold plug, sanded to 1500 and then added wax on top. The tooling gel coat heated the spray primer and took all of it off when I pulled the mold off.

    Can I pull a mold directly off epoxy (with wax of course)?

    Or what would be a great material to use for the final surface of the plug since I don't have spray equipment? I can only brush
     
  2. jorgepease
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    jorgepease Senior Member

    I'd gelcoat it, roll it carefully if you can't spray then you can sand her down a bit and then wax it plus use a mold release agent as well till the mold is seasoned
     
  3. aaronhl
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    aaronhl Senior Member

    Cool I'm going to try that, hopefully rolling (plus tipping) will make it somewhat smooth to start sanding
     
  4. aaronhl
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    aaronhl Senior Member

    So you wouldn't recommend pulling a poly mold from an epoxy plug?
     
  5. jorgepease
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    jorgepease Senior Member

    Im sure you could wax epoxy, never tried it. When you wax your new molds, you need to do it like 8 times. Then use PVA or other mold release agent over that. After awhile the wax buildup will require less coats.

    Im not an expert in molds, I'v just started using them myself, so maybe others will chime in with some tips.
     
  6. ondarvr
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    ondarvr Senior Member

    The reason it came off has little to do with heat, very few primers (or paints) will hold up to the styrene in gel coat.

    You can use the epoxy as a mold surface.

    If you want to use something over the epoxy, use Duratec sanding primer, it will do a good job of bonding to the epoxy, and will be easy to sand.
     
  7. gonzo
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    gonzo Senior Member

    If you use epoxy, make sure all the amines are washed off. They act as a cure inhibitor for polyester resins.
     
  8. garrybull
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    garrybull Senior Member

    i second using duratec surface primer.

    easy to use and sand and it polishes up nicely as well to take a mould from it.
     
  9. aaronhl
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    aaronhl Senior Member

    Good info guys, can I roll/brush the Duratec surface primer on?
     
  10. ondarvr
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    ondarvr Senior Member

    Yes, but it will still have some texture.

    Sand the epoxy with 80 grit prior to applying the Duratec.
     
  11. aaronhl
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    aaronhl Senior Member

    OK Good to know, I know Duratec sticks to a lot, but polyester not so much.

    If I put poly gelcoat over epoxy it wont stick? Should I sand it down to 80 grit to make sure the gelcoat sticks? Because right now I have gelcoat and not duratec
     
  12. ondarvr
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    ondarvr Senior Member

    Hard to say if it bond very well, too many variables.
     
  13. aaronhl
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    aaronhl Senior Member

    Interesting I am going to try this tonight
     
  14. jorgepease
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    jorgepease Senior Member

    aaronhl, it should bond well enough for the use if the epoxy was correctly mixed and fully cured. Wash it and sand it apply your gelcoat and make sure to wax is multiple times before you use it. multiple layers of wax will help prevent a repeat experience.
     

  15. aaronhl
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    aaronhl Senior Member

    Yea this isn't a structural project just a quick surface to pull a mold off...I just rolled the polyester gelcoat on the piece after sanding at 60 grit. This is the first time I rolled gelcoat and it was pretty neat actually I didn't think it would come out that nice and smooth. Now I see why gelcoat is used because its really stickyyy and not too thick. Epoxy just runs and is pretty thick

    If I want to build up a gelcoat surface, can I roll a coat, wait half an hour and roll another one, and so on? It seems like no matter how much gelcoat I loaded on the roller it wouldn't thicken the layer.
     
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