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Hearth insulation layer - Forno Bravo Forum: The Wood-Fired Oven Community


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Hearth insulation layer

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  • Hearth insulation layer

    Hello all, working on foundation for an earth oven, up to the insulation layer for the hearth and had some questions,

    Just wanted be sure I understood the mix. Portland cement and vermiculite mixed ratio of 5 or six to one, (I assume the measure is by volume in dry state for both) nothing else added like sand or rock. Also, I read one of the threads where someone had better success by mixing the Portland cement separately into kind of slurry and adding it to the vermiculite in a separate container than mixing into kind of an oatmeal state. Oh, how about the reinforcing rods, I am pouring a 6.5 diameter circular base, seems some say rods on 12 inch centers and others on 8 inch centers. Or can the wire screen be substituted.

    Thanks for the advice!!

  • #2
    Re: Hearth insulation layer

    six to one is fine. No sand or gravel. Mixing a slurry first is simpler. When mixing the vermiculite and cement - mix gently (by hand not machine) so as not do break down the vermiculite particles and reduce insulation value.

    For rebar in the suspended slab, I suggest either 8 inch spacing for 1/5 inch diameter rebar or 6 inches for 3/8 inch rebar (the 3/8 is much easier to work with). Both ways, in a grid. Re-bar is cheap. Wire mesh (WWF) should not be substituted for rebar.