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  1. RPF Premium Member TylerHam's Avatar
    Member Since
    Nov 2009
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    Northern California
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    Oct 19, 2011, 1:23 PM - Working with Bondo on Styrofoam tips? #1

    Hi All

    I like the theory of Bondo over foam, etc - But I can NEVER get it to work right - It always hardens too fast, wont sand well (too hard) etc -

    Is there a trick to using it? Is Bondo-glass easier to use (The Bondo fiberglass)

    Any help would be great! Thank you!
  2. RPF Premium Member slimesquare's Avatar
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    Nov 2009
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    Oct 19, 2011, 1:26 PM - Re: Working with Bondo on Styrofoam tips? #2

    try using rondo....mixture of fiberglass resin and bondo. use a half and half mixture and adding a little extra resin to it will make it pourable, or brushable
  3. RPF Premium Member TylerHam's Avatar
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    Northern California
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    Oct 19, 2011, 1:31 PM - Re: Working with Bondo on Styrofoam tips? #3

    never heard of doing that! So do you add the hardener to the "rondo" that the bondo uses after its mixed? Or do you add the hardener to the bondo before mixing?
  4. Contec's Avatar
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    Oct 19, 2011, 1:37 PM - Re: Working with Bondo on Styrofoam tips? #4

    you mix bondo and resin well first, then you use the harderner.
  5. scorpion's Avatar
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    Oct 19, 2011, 1:42 PM - Re: Working with Bondo on Styrofoam tips? #5

    i think is impossible, i use bondo over cardboard works perfect, i made this while ago card+bondo

    http://www.therpf.com/f9/patlabor-av...rs-tall-98947/
  6. aron42486's Avatar
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    Ocala, FL
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    Oct 19, 2011, 2:33 PM - Re: Working with Bondo on Styrofoam tips? #6

    If memory serves me well...

    You want to use the resin catalyst as opposed to the bondo hardener for the mixture.

    Double check that just in case I am mistaken
  7. RPF Premium Member slimesquare's Avatar
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    Oct 19, 2011, 4:07 PM - Re: Working with Bondo on Styrofoam tips? #7

    aron42486 said: View Post
    If memory serves me well...

    You want to use the resin catalyst as opposed to the bondo hardener for the mixture.

    Double check that just in case I am mistaken
    i've always mixed both hardeners and its worked fine
  8. Majestic 3 RPF Premium Member sean's Avatar
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    Jacksonville. Fl
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    Oct 19, 2011, 7:35 PM - Re: Working with Bondo on Styrofoam tips? #8

    Bondo doesn't melt Styrofoam?
  9. RPF Premium Member
    Member Since
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    NZ
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    Oct 19, 2011, 7:58 PM - Re: Working with Bondo on Styrofoam tips? #9

    I use a coarse half-round file or rasp on bondo to get the basic shape then sand. Also several thin layers to build up the shape you want is better than one thick layer.

    If it sets too fast you're probably using too much hardener.

    For foam I'd be tempted to apply a layer of fiberglass first for strength then bondo over that. Then you could melt the foam with solvent to leave a hollow shell.

    TylerHam said: View Post
    Hi All

    I like the theory of Bondo over foam, etc - But I can NEVER get it to work right - It always hardens too fast, wont sand well (too hard) etc -

    Is there a trick to using it? Is Bondo-glass easier to use (The Bondo fiberglass)

    Any help would be great! Thank you!
  10. xenobiologist RPF Premium Member Leigh's Avatar
    Member Since
    Jul 2011
    From
    Cambs, UK
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    1,096
    Oct 20, 2011, 12:33 AM - Re: Working with Bondo on Styrofoam tips? #10

    I'm assuming your Bondo is basicly the same thing as our P38 or Easysand, A polyester resin with chalk dust ?

    I've been using it in the motor trade for many years & on my foam based project. I also would have thought it would melt Styrofoam being styrene based, I used insulation foam on mine & PVA to seal the foam prior to using the filler.
    I've personaly not found the need to add more resin but you can reduce the curing time by using slightly less hardener & as said build it up in thin layers. I also always take advantage of the Semi cured time when its setting but not quite set its a bit like cheese, when its like that you can carve it really nicely to knock down the sanding work.
    I always use 80 grit aluminium oxide paper for the bulk of the shaping & then a finer 180-240 grit to remove the 80 grit scratches.
    Also if your covering a larger curved area use a rubber spreader to apply it & Dont play with it too much looking to get the perfect finnish first go.

    HTH
  11. Contec's Avatar
    Member Since
    Jun 2008
    From
    Sweden
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    Oct 20, 2011, 5:06 AM - Re: Working with Bondo on Styrofoam tips? #11

    you can cover the styrofoam with aluminumfoil before useing the rondo/bondo... Also there is another typ of foam that some people use (pink foam?) that do not melt when resin is applyed.
  12. Majestic 3 RPF Premium Member sean's Avatar
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    Jacksonville. Fl
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    Oct 20, 2011, 10:41 PM - Re: Working with Bondo on Styrofoam tips? #12

    Leigh said: View Post
    I'm assuming your Bondo is basicly the same thing as our P38 or Easysand, A polyester resin with chalk dust ?

    I've been using it in the motor trade for many years & on my foam based project. I also would have thought it would melt Styrofoam being styrene based, I used insulation foam on mine & PVA to seal the foam prior to using the filler.
    I've personaly not found the need to add more resin but you can reduce the curing time by using slightly less hardener & as said build it up in thin layers. I also always take advantage of the Semi cured time when its setting but not quite set its a bit like cheese, when its like that you can carve it really nicely to knock down the sanding work.
    I always use 80 grit aluminium oxide paper for the bulk of the shaping & then a finer 180-240 grit to remove the 80 grit scratches.
    Also if your covering a larger curved area use a rubber spreader to apply it & Dont play with it too much looking to get the perfect finnish first go.

    HTH

    what is PVA?
  13. xenobiologist RPF Premium Member Leigh's Avatar
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    Cambs, UK
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    1,096
    Oct 20, 2011, 11:52 PM - Re: Working with Bondo on Styrofoam tips? #13

    sean said: View Post
    what is PVA?
    From Wikipedia:

    "Polyvinyl acetate is a component of a widely-used type of glue, referred to variously as wood glue, white glue, carpenter's glue, school glue or PVA glue."


    http://www.homebase.co.uk/webapp/wcs...tNumber=757458

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