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Thread: using expanding foam behind panels

  1. #1
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    using expanding foam behind panels

    this is on a 355 rebody, planning to fill the hollows with expanding foam.

    My main question, is if you put too much foam in and it tries to continue expanding does it actually exert force and potentially alter the panel shape ? ( i presume you could minimise this by providing a number of relief / vent holes )

    Or does the foam just become denser if it cant 'move' as it expands ?

    For anyone thats done their car with this , any drawbacks or comments on foam filling ?, would you recomend doing it ? ie no reactions with the grp resin etc ?

    thanks, nick


  2. #2

    Re: using expanding foam behind panels

    I saw someone do this on a first gen Viper. It did warp the door.

  3. #3
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    Re: using expanding foam behind panels

    Quote Originally Posted by nick200
    this is on a 355 rebody, planning to fill the hollows with expanding foam.

    My main question, is if you put too much foam in and it tries to continue expanding does it actually exert force and potentially alter the panel shape ? ( i presume you could minimise this by providing a number of relief / vent holes )

    Or does the foam just become denser if it cant 'move' as it expands ?

    For anyone thats done their car with this , any drawbacks or comments on foam filling ?, would you recomend doing it ? ie no reactions with the grp resin etc ?

    thanks, nick

    Nick, go to your bodyshop supplier and tell them what you are looking for. OE cars have foam in them too. But, not the home depot variety. FUSOR, SEM, and others make foams in various densities, flexible and rigid. Quality bodyshops use them all the time when replacing qtr panels, rockers, etc where there was originally factory foam. I would not use the "great stuff" or anything like that though.

  4. #4
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    Re: using expanding foam behind panels

    Quote Originally Posted by bartman
    Quote Originally Posted by nick200
    this is on a 355 rebody, planning to fill the hollows with expanding foam.

    My main question, is if you put too much foam in and it tries to continue expanding does it actually exert force and potentially alter the panel shape ? ( i presume you could minimise this by providing a number of relief / vent holes )

    Or does the foam just become denser if it cant 'move' as it expands ?

    For anyone thats done their car with this , any drawbacks or comments on foam filling ?, would you recomend doing it ? ie no reactions with the grp resin etc ?

    thanks, nick

    Nick, go to your bodyshop supplier and tell them what you are looking for. OE cars have foam in them too. But, not the home depot variety. FUSOR, SEM, and others make foams in various densities, flexible and rigid. Quality bodyshops use them all the time when replacing qtr panels, rockers, etc where there was originally factory foam. I would not use the "great stuff" or anything like that though.

    I agree. The stuff from HP or Lowe's will expand too much. You need a very low expanding foam or it will distort your parts. Even providing holes for it to expand out of will not work.

  5. #5
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    Re: using expanding foam behind panels

    Are these foams flammable? What with everything happening to Ferrari at the mo with its cars bursting into flames due to a glue used in the wheel arch. Are the foams safe to be used in panels near the engine? Will they soften with heat?

  6. #6
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    Re: using expanding foam behind panels

    This site is probably expensive but go to www.aircraftspruce.com and search for liquid foam or
    X-30 foam. We use it in aircraft, should be good for cars or boats.

  7. #7
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    Re: using expanding foam behind panels

    thank you for your replies, always good to know of any potential risks when we have all spent so long on making our cars.

    I shall seek down some low expanding foam and give that a go, nick.

  8. #8
    Senior Member lambochik's Avatar
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    Re: using expanding foam behind panels

    i actually used the lowes brand "good stuff" and it pushed out a body kit on my brothers 240sx. the driver side looked nice and clean and slinder, but the passanger side was fat, pushed out, warped, widebody looking. we tried the stuff one more time on a neon bodykit and it work perfectly. the difference; on the 240 bodykit it was sprayed in avery tight are above the wheel area, and on the neon it was sprayed behind a bumper and had 2 area it could continue to expand. if u use this stuff, make sure it has a place to go. and i suggest spray the center of what your filling let it "cure" then spray the ends. just do it in stages and it wont be able to warp the bumper. just my $2. that means it worth more then 2 cents.

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