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Thread: body filler for styrofoam

  1. #1
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    body filler for styrofoam

    I'm very new in fiberglass and molding, so the question below is to start some self-training before going to build big fiberglass parts for a kitcar.

    My idea is to start with a styrofoam plug to take the molds from it. As I'm modelling it and sanding the model (plug), I will need to fill up gaps, imperfections and mistakes with polyester-free body filler, and I heard automotive body fillers are the wrong way to go. Is that right? Any alternative?

    So then I could use latex painting on the finished plug (well coated in thin layers, sanded in between, etc) to protect from polyester resin when laying the fabric. Would that work?

    Thanks,

    Marcio.

  2. #2
    Super Moderator Alex's Avatar
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    You are correct that anything polyester will melt Styrofoam. You can use epoxy based fillers and coat the plug with epoxy too, this will provide a good coating to take a polyester mould off (ensure epoxy is fully cured before using and don't forget release agents, obv.). So, sticking with the Styrofoam I would suggest a tin of either Petram or west system epoxy resin. Use some 409 or 407 filler to turn some of the epoxy into a bodyfiller. Use the remaining epoxy as a 'varnish' to protect the sytrofoam from the polyester solvents.

    Alternately, ditch the Styrofoam and use a polyurethane based foam like this or kingspan or celotex building insulation. They are fine with all resin types.
    Last edited by Alex; 27-04-2016 at 08:58. Reason: head not screwed in correctly

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    Hang on, is celotex insulation actually PU based? So coming back to my question, can I use celotex to get a rough shape then apply automotive body filler (e.g. bondo) to sand and get final glossy shape? Then lay up fiberglass using polyester resin, everything as a normal human being? Because it's a personal project (err, a 13ft long car body) I'm out of budget this month, but I want to buy some celotex board some time next month for some experiment. I will keep posted (either by this thread or new one, depending how long it's going to take).

    Thanks,

    Marcio.

  4. #4
    Super Moderator Alex's Avatar
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    Marcio,

    Yes to everything. My only advice with celotex is that once you have sanded your rough shape, get the surface sealed up with a coat of polyester resin. The foams surface is a bit fragile and SO absorbant it tends to dry everything out and is difficult to bond to.

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    Alex,

    Sorry to bring this thread back to life after so long.

    So, I'm carrying on the project, I have a pattern surface where I used parts of celotex and part with expanding form to shape my pattern. I have approximately the shape I want and now it’s time to apply polyester resin on it before body filler. It’s not finished yet but it’s time to work out my future spends.

    You advised to apply a coat polyester resin then body filler. What and how can I use? I might need some details, like mixing portion, specific products, tools etc. I imagine for body filler I need the past + hardener, what about the resin? Would I need to sand my pattern more in order to account the additional thickness of resin + bondo?

    http://i53.photobucket.com/albums/g6...psfvur4bbu.jpg

    Thanks,

    Marcio.

  6. #6
    Super Moderator Alex's Avatar
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    yes, you should expect the foam to be smaller and the final size will be based on the bondo. Plus, normally a coat of polyester spray surfacing primer as the final pattern surface.

    So, for priming all that dusty foam use:
    GP Polyester Resin

    Find some nice bondo here:
    Body Fillers

  7. #7
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    great stuff! thank you so much

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