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Insulated Hearth - Forno Bravo Forum: The Wood-Fired Oven Community


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Insulated Hearth

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  • Insulated Hearth

    I've found a product called Zonolite. It is vermiculite with an additive that reduces or prevents the vermiculite from absorbing moisture. It is manufactured and sold by GraceConstruction. It is a loose insulation that is used for insulating cement blocks by pouring it into the holes in the cement blocks.
    Has anyone else heard of this product and can I use this material and mix it with cement to make the insulated hearth?

    If nothing else, I will use it to fill in around the dome. I have been having a problem trying to find bulk vermiculite that is cheap.....
    Last edited by Spunkoid; 08-17-2009, 08:39 PM.

  • #2
    Re: Insulated Hearth

    A VERY quick google tells me to RUN! This may be old data - a common issue w/ the web. The vermiculite we are buying today is free of the nasty stuff (Or so we are told).This could be a dump

    WR Grace mined vermiculite in Libby Montana during the 1960's and 1970's and packaged it as insulation under the trade name Zonolite. Grace also had a number of processing plants around the United States where it turned the mined vermiculite into Zonolite. Zonolite was sold nationwide until about 1985. The Federal Government estimates that it may have been used as insulation in as many as 35 million homes. The Environmental Protection Agency warns that if Zonolite dust is inhaled, it can create significant health risks, including asbestos-related diseases.
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    • #3
      Re: Insulated Hearth

      Zonolite as manufactured and sold today contains no asbestos. It would be illegal to sell. In fact, I asked that question as I remember the Zonolite of old and remember the ads on TV for attic fill. I also remember the class action lawsuits that settled for big bucks.
      As an insulative material only, it should be fine and is commonly used. ...but my question remains, can or should I use it for the insulative hearth?


      • #4
        Re: Insulated Hearth

        I would imagine that whatever it is coated with would make it hard to bond with the cement, leaving the insulation too loose to support the dome. IIRC, there was some issue with silicone-impregnated vermiculite mentioned in the FB plans. Whatever the chemical agent, I would worry about it reacting at temperature.

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