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Options for oven floor insulation and construction

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  • Options for oven floor insulation and construction

    I am still at the planning stage though I have about 50% of my bricks cut before our Irish wet season started.

    I intend covering my hearth with polished granite as an impervious layer on which my underfloor insulation will sit. As the granite comes in 1m square tiles I’ll place weep holes to permit drainage.

    I would like some advice regarding insulation under the oven floor. From various pictures I see two options.
    1. The insulation it trimmed to match the shape and size of the oven ie circular.
    2. The insulation and oven floor are rectangular and much wider than the finished dimensions of the oven.
    Option 1 uses less insulation, my preference since insulation here is difficult to get and expensive. However, this involves more floor brick cutting to match the shape. I assume any oven or oven floor expansion compresses the insulation blanket around the inner oven wall.

    Option 2, If I use this method do I need to have something around the outer layer of floor bricks to keep the oven floor from moving. Would cementing the outer row of bricks to the granite keep it stable or would this inhibit floor expansion. Do I need to allow for floor expansion?

    Any suggestions as always welcome.

  • #2
    What size is your base and what size is your oven?

    Wont it be a bit wasteful and expensive laying polished granite under the dome?

    I always cut my ceramic board 5” bigger than the dome so the the bricks dont rest right on the edge of the board!

    Have you considered laying the granite at the same level as the oven landing, wont your suggested method see the granite around 7” lower than the oven floor surface?
    If you put the granite down first then 4” of insulation then 3” of brick .

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    • #3
      Originally posted by dogshark58 View Post
      I am still at the planning stage though I have about 50% of my bricks cut before our Irish wet season started.

      I intend covering my hearth with polished granite as an impervious layer on which my underfloor insulation will sit. As the granite comes in 1m square tiles I’ll place weep holes to permit drainage.

      I would like some advice regarding insulation under the oven floor. From various pictures I see two options.
      1. The insulation it trimmed to match the shape and size of the oven ie circular.
      2. The insulation and oven floor are rectangular and much wider than the finished dimensions of the oven.
      Option 1 uses less insulation, my preference since insulation here is difficult to get and expensive. However, this involves more floor brick cutting to match the shape. I assume any oven or oven floor expansion compresses the insulation blanket around the inner oven wall.

      Option 2, If I use this method do I need to have something around the outer layer of floor bricks to keep the oven floor from moving. Would cementing the outer row of bricks to the granite keep it stable or would this inhibit floor expansion. Do I need to allow for floor expansion?

      Any suggestions as always welcome.
      Option 1 is the only option. The floor bricks can not extend out past the dome bricks or will be a point of significant heat loss.

      The floor bricks can either be cut to the inside of the dome bricks or the outside. Cutting to the inside of the dome can be more meticulous whereas to the outside you can be pretty rough as they get covered by the dome insulation.

      Comment


      • #4
        I’m not sure that granite is a suitable material as it does not like heat. Particularly if the granite slab is both under the oven and extends out past the outer rendered shell. The difference in thermal expansion between that part which is being heated and the cooler outer part in ambient temperature is sufficient to crack it. This is exactly the scenario I observed on an oven I was doing repairs on last year. I think I’ve also read the same from members reports on this forum. It would be better to cut the granite so it does not sit under the floor insulation IMO. The concrete slab can be sealed to prevent wicking moisture before placing the insulation board.
        Last edited by david s; 03-02-2022, 12:37 PM.
        Kindled with zeal and fired with passion.

        Comment


        • #5
          Originally posted by dogshark58 View Post
          I am still at the planning stage though I have about 50% of my bricks cut before our Irish wet season started.

          I intend covering my hearth with polished granite as an impervious layer on which my underfloor insulation will sit. As the granite comes in 1m square tiles I’ll place weep holes to permit drainage.

          I would like some advice regarding insulation under the oven floor. From various pictures I see two options.
          1. The insulation it trimmed to match the shape and size of the oven ie circular.
          2. The insulation and oven floor are rectangular and much wider than the finished dimensions of the oven.
          Option 1 uses less insulation, my preference since insulation here is difficult to get and expensive. However, this involves more floor brick cutting to match the shape. I assume any oven or oven floor expansion compresses the insulation blanket around the inner oven wall.

          Option 2, If I use this method do I need to have something around the outer layer of floor bricks to keep the oven floor from moving. Would cementing the outer row of bricks to the granite keep it stable or would this inhibit floor expansion. Do I need to allow for floor expansion?

          Any suggestions as always welcome.
          It would be impossible to cement bricks to and underlying layer of smooth granite. Basically, you're proposing an oven that will try to slide around on a smooth granite surface. It would make far more sense to only use granite around the outside of your oven.
          My 42" build: https://community.fornobravo.com/for...ld-new-zealand
          My oven drawings: My oven drawings - Forno Bravo Forum: The Wood-Fired Oven Community

          Comment


          • #6
            Originally posted by MarkJerling View Post

            It would be impossible to cement bricks to and underlying layer of smooth granite..
            OP said the insulation was going on top the granite.

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            • #7
              Originally posted by Pizzarotic View Post

              OP said the insulation was going on top the granite.
              I was responding to this question by the OP:

              Originally posted by dogshark58 View Post
              Option 2.....Would cementing the outer row of bricks to the granite keep it stable or would this inhibit floor expansion....
              Bricks can't be cemented to smooth granite. Heat proof silicone, maybe, but cement would not work.
              My 42" build: https://community.fornobravo.com/for...ld-new-zealand
              My oven drawings: My oven drawings - Forno Bravo Forum: The Wood-Fired Oven Community

              Comment


              • #8
                The one-piece granite slab of our oven had the dome cut out. My brother-in-law got a nice round table out of it. Resting the entire oven on top of the granite is possible, I suppose, but seems a bit silly.

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