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Base design thoughts

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  • Base design thoughts

    G'day from Australia. I'm a new member and base work is commencing tomorrow. Great forums and comments.
    I have the foundation down and have a question for anyone with time to help. I am following the Forono Bravo Pompeii Oven Instructions. In relation to the structural support and insulation layer they state;
    "Your oven sits on a two-layer hearth, comprised of an insulating layer that rests directly under the oven cooking floor, and a structural layer that hold the oven in place. The insulating layer stops heat from leaving the oven through the cooking floor, and is made from either 2” ceramic fiber insulating board (FB Board), or 3 ” or 4” of insulating concrete (vermiculite or perlite mixed with Portland cement). The structural layer is comprised of either 3 “ of rebar reinforced concrete, or a fabricated metal tray"
    I have slightly different dimentions, 6 and 3/4 inch thickness available for structural and insulation layer. I could possibly build for additional thickness but 6 and 3/4 inch works with my current plan and they suggest the board is better. My question is;
    if I pour a 4 and 3/4 inch reinforced structural layer can I then simply at the same time position the 2 inch insulation board on top and pour concrete around that to create even flat base? I would then lay the oven floor bricks directly over this surface, that is some bricks directly on the board and the bricks around the outer edge on the concrete.
    Also, is calcium silicate board or ceramic fibre insulation board better? Can get either here in Aus.
    Thanks in advance
    Adelaide, Australia.

  • #2
    The FB plans are a good baseline but a little dated. There have been many improvements since the original edoc was published. 2" of CaSi board is the bare minimum, 3" better. The ceramic fibre insulation board you talk about, may work but you really need to look at the specs, two major specs. K value in the area of 0.55 at 500 F and compression strength of at least 75 PSI, sorry, you will have do the metric conversion. Floor and dome fire brick must "NOT" touch the concrete hearth (it will act as a heat sink) and must have insulation under the fire brick.
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    • #3
      Ok many thanks for your reply. I can source the calcium silicate board which is good. I will confirm its compressibility and if at least 75 psi would you think the whole dome and floor fire bricks should sit directly on the insulation, prevent the heat sink?
      Adelaide, Australia.