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Oven floor - Forno Bravo Forum: The Wood-Fired Oven Community


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Oven floor

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  • Oven floor

    Hi guys and gals,

    I have been thinking about my oven design before I start the building and have had some thoughts about the oven floor. In a traditional kiln the fire bricks are not cemented in and have expansion joints. What I have been wondering is should the floor actually make contact with the oven wall?

    The bricks will expand under heat and if the walls are attached to the floor wouldnt that mean that the movement will cause cracks in the dome? Is there anything stopping the oven floor from having for example a 4 mm gap between the wall and the floors all around ? and the walls actually sitting on insulation bricks along the outside of the floor.

    Has anyone tried this approach, would this design cause a longer heating time? Is there a design flaw in this approach ?? Does the floor bricks even need to be cemented down or can they just be placed inside?


  • #2
    Re: Oven floor

    Hi Imran,

    I think the official design plans actually have the floor bricks just sitting on a thin layer of sand and fire clay dust (I used what was produced from cutting the bricks in half). And someone - can't remember was it Les of Ken? - made a beautiful gap between the floor and the walls of their oven. I have a gap too, but mine is due to inexact cutting...

    So basically you are bang on line with your thoughts. Yes its a good idea to leave a gap and just place your bricks on the floor, and no it won't cause longer heat up time.

    Does anyone remember where those pics were?
    "Building a Brick oven is the most fun anyone can have by themselves." (Terry Pratchett... slightly amended)



    • #3
      Re: Oven floor

      The bricks on the floor will expand with heat, but so will the dome. I know I'm in the minority, but I think the dome should be built on the floor, rather than on the insulating layer, because the firebrick liner will expand as a unit, and the horizontal floor edge bricks will spread the weight of the dome over a larger footprint. Both methods of construction work fine.

      The floor bricks can just be laid loose on the insulating layer. If you are using a well leveled set of insulating boards, you can just lay the bricks down on this, as I did.

      By the way, any gap between floor and dome will quickly fill up with wood ash. I wouldn't worry about keeping an open expansion joint here.

      If you are using vermiculite concrete, which will have a rough and uneven surface, you put down a layer of sand and fireclay, or fire brick dust, to get a level surface to put your bricks on. Current thinking is to put this layer down dry, lay your bricks the way you want them, and then saturate the bricks with water to solidify the clay underneath.
      My geodesic oven project: part 1, part 2


      • #4
        Re: Oven floor

        Is there any reason you can't replace the floor bricks if you put the dome directly on the cooking floor? I hear alot of people say they like the dome on the insulation because they want to be able to replace the floor but it seems like you could still replace 85% of the floor bricks. The ones that would wear out seem like the ones that are not under any part of the dome and could be replaced. Am I missing something?


        • #5
          Re: Oven floor

          I've been meaning to post this graphic for a while. It shows how the precast ovens work, with the dome sitting on the insulating layer -- around the cooking floor. There is an expansion/contraction gap between the dome and floor.

          For folks building a Pompeii Oven, I think this is also helpful.

          I think it's right to say there is no "right".

          You can set the dome on the cooking floor or on the insulating layer. From a cooking and thermal perspective, it is better for the dome to wrap around the floor, and all of the FB pre-made ovens work that way The dome "fits" around the floor.

          For Pompeii Oven builders, there are other trade-offs. It is easier to build the dome directly on top of the cooking floor, and there is some thinking that the dome is more structurally solid that way, as it rests on a solid brick floor, rather than the less rigid insulating floor.

          Check out the graphic.
          Attached Files
          Last edited by james; 04-14-2008, 07:35 AM.
          Pizza Ovens
          Outdoor Fireplaces


          • #6
            Re: Oven floor

            Originally posted by james View Post

            I think it's right to say there is no "right".

            Check our the graphic.
            Hey, nice graphic...looks a lot like my oven.

            I agree on this one but lean toward David's on-hearth preference.

            There have been so many cats skinned in so many ways.

            do what feels right for you......it will cook!
            sigpicTiempo para guzarlos..... ...enjoy every sandwich!


            • #7
              Re: Oven floor

              I think that's one of the really cool aspects of the pompeii oven plans. You start out thinking: I'll build an oven exactly like that!

              But when you start building you realise there are so many decisions to make and so many variations to choose from, and what you end up with is a unique oven you created yourself.

              beaglestorm, your line of thought makes sense to me too, I'm sure it will work out well if you do it that way.

              Personally I couldn't see that it mattered much either way when I was at this stage, so I went for the version I thought would be easier to build...
              "Building a Brick oven is the most fun anyone can have by themselves." (Terry Pratchett... slightly amended)



              • #8
                Re: Oven floor

                The 4 mm gap that you suggest - is that just a random number? Someone, perhaps dmun has given the percentages of themal expansion that the firebricks undergo when heated. Something like .021?? Anyway, it sounded at the time like you should be able to calculate how much gap space to leave.

                Robert or anyone else - how did you come up with your numbers for the gaps you left?
                Everyone makes mistakes. The trick is to make mistakes when nobody is looking.