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Hearth slab size for 42" oven? - Forno Bravo Forum: The Wood-Fired Oven Community

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Hearth slab size for 42" oven?

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  • Hearth slab size for 42" oven?

    thanks, James, for the forum. But this is open to anyone with experience.

    I'm in the process of preparing the site for a 42" oven. However, I want to make some small adjustments to accomodate a 12"-thick stone facade and copper hood. How large does the hearth need to be, just to accomodate the oven dome? (42" plus thickness of the actual done and thin cladding)

    There has been some recent discussion about keeping the hearth as small as is actually needed for cooking, rather than accomodating the landing, etc. I believe I would do better to build a suspended hearth (a la Bread Builders) and let the outerstructural walls sit directly on the cinderblock base walls.

    Any direction would be helpful, especially from those who've actually built already.

    Thanks, in advance, for your help.

    Michael

  • #2
    The thermal mass of the hearth needs to be the same size as your brick hearth. The rest is entirely structural or cosmetic. I've posted some stuff on building an "island hearth" where the thermal mass concrete is placed under the oven and is surrounded by insulating concrete (vermiculite concrete mix).

    More thermal mass is excessive and will reduce the efficiency of the oven (in terms of cooking time -- more mass tends to wick heat away from the brick hearth faster than it can recharge from the fire when you're cooking pizza).

    Jim

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    • #3
      42" Dome Hearth measurements

      I'm sorry, Jim. I look back and realize I did a poor job of wording my question.

      I would like to make a 42" firebrick dome and and wondering about the optimal width and length of the hearth slab. I don't want to make it any larger than is truly beneficial, and assume that it really only needs to be directly below the dome, not extended to the sides as some of the pictures I've seen. I had intended to build a suspended (isolated) slab as recommended by The Bread Builders' plans, but am wondering what difference it makes.

      I see that the current recommendation is to build a floating slab on top of the cinderblock base walls. Is that simply because of the ease of construction, or is there an other reason for extending well beyond the actual dome walls?

      I know you have experience with both--perhaps the only one who has "swung both ways". So your input would be appreciated.

      Thanks, Michael

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      • #4
        Hi Michael,
        I've seen it written elsewhere that the rebar itself deteriorates over time(due to rust and heat) and so does not provide a safe stable support for the cooking floor slab .From comparing the two methods-it seems to me the safest way to go is over the cinder block,
        David

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        • #5
          Originally posted by PizzaMan
          I would like to make a 42" firebrick dome and and wondering about the optimal width and length of the hearth slab. I don't want to make it any larger than is truly beneficial, and assume that it really only needs to be directly below the dome, not extended to the sides as some of the pictures I've seen. I had intended to build a suspended (isolated) slab as recommended by The Bread Builders' plans, but am wondering what difference it makes.

          I see that the current recommendation is to build a floating slab on top of the cinderblock base walls. Is that simply because of the ease of construction, or is there an other reason for extending well beyond the actual dome walls?

          Thanks, Michael
          The reason Alan recommends the floating/suspended hearth is because adding 8" of concrete to all sides increases the mass even beyond what his design can effectively use. But, it is *far* easier to build than the hanging hearth and doesn't have any issues with potential rebar failure dropping the hearth on the ground. The island hearth design I posted enjoys the benefit of the ease of construction of the wall-to-wall hearth but only has the thermal mass the oven needs.

          Jim

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