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Thread: Moldmaking question

  1. #1
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    Moldmaking question

    How do you cover a plastic beachball with polyester resin and mat, and not have it eat the plastic. I already tried this and the ball split at the seams.
    Has anyone ever coated the plastic with paper mache, then followed with resin/mat? Thanks
    And the joke is,<br />when he awoke his,<br />body was covered in Coke fizz !

  2. #2
    Senior Member wbnemo1's Avatar
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    Re: Moldmaking question

    paper mache' works, so does plaster

  3. #3
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    Re: Moldmaking question

    i would try coating it real good with shelac

  4. #4

    Re: Moldmaking question

    you can also cover the ball with stripes of aluminum foil. You can spray contact glue (3M super 77) to hold the pieces in place. I did it on foam sheet and it worked very well. Just make sure you don't have any uncovered areas. It's also somewhat easy to peel off the foil from the fiberglass

  5. #5

    Re: Moldmaking question

    Quote Originally Posted by Daleford
    How do you cover a plastic beachball with polyester resin and mat, and not have it eat the plastic. I already tried this and the ball split at the seams.
    Has anyone ever coated the plastic with paper mache, then followed with resin/mat? Thanks

    Masking tape will work. Not cheapo stuff either.

    ;D

  6. #6
    Senior Member RCR's Avatar
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    Re: Moldmaking question

    How about a good coat of latex paint?

    Bob
    Bob custom '84 Fiero SE --->>> custom F408
    http://www.madmechanics.com/forum/cu...ilepic37_1.gif

  7. #7
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    Re: Moldmaking question

    Thanks for the help. Lets take this a bit further. I want to build a "one time" 5 foot tall fiberglass football helmet for a local collage sports division. I will then mount the helmet on a golf cart and paint the helmet the collage colors. My plan was to cover a 6 foot tall plastic beach ball with polyester resin and mat. Then coat it with bondo and sand it out smooth before painting. One heck of a lot of sanding and all convex surfaces!
    As I said earlier, the polyester resin was too aggressive on the small plastic beach ball we tried it on so now I have to try somthing else. If I went with the paper mache I feel I could retain most of the round surface and hopefully it wouldn't take too much bondo to smooth it out.
    Questions: How long will it take to lay a couple layers of paper mache on a 6 foot ball?! How easy to lay a couple coats of mat and resin on that mache covered ball?
    Am I missing an easier method? Could I make a low cost paper mache mold, remove the beach ball liner and simply build my fiberglass helmet on the inside of it? This way I would be taking advantage af the smooth inside of the paper mache and eliminate the bondo/sanding step. Then I could discard the outer mache shell. I will try to attach a pic of an actual golf cart helmet.
    And the joke is,<br />when he awoke his,<br />body was covered in Coke fizz !

  8. #8
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    Re: Moldmaking question

    Golf cart
    Attached Images Attached Images  
    And the joke is,<br />when he awoke his,<br />body was covered in Coke fizz !

  9. #9
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    Re: Moldmaking question

    Quote Originally Posted by Daleford
    Golf cart
    Two make this helmet smooth on the inside and outside I would try on of two methods.
    1) Make two molds one the inner and one the outer and then bond them together (same idea as a car hood). Use a high build primer on shiney surfaces and cover that with dry wall plaster then shape and sand that smooth. Paint with a high gloss enamel, wax, mold release and lay up mold. If planning on more than one add flanges and make into RTM molds.
    2) Make one very smooth helmet them vacumn mold so outer surface is smooth.

    Hope this helps ....


  10. #10
    Senior Member Jets303's Avatar
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    Re: Moldmaking question

    My take:

    I would start with covering the entire ball with two layers of good masking tape. Try and layer them as smooth as you can. Spray down some PVA or mold release or both. Lay up a couple thin coats of gel coat eventually building up to a thick one but avoiding to much heat at once. Followed by some serious glass buildup. Once you've cured, pop the ball and pull your mold. Lay up the mold and pull your first shell. I would stay away from glassing it right on the ball, you're gonna have a hell of a time bondoing and glassing it from the outside, plus getting those pits out will take hours!

    I think this is your best bet or something similar. Hope that helps

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