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General Question - Forno Bravo Forum: The Wood-Fired Oven Community


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General Question

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  • General Question

    This is my first post - hope I'm putting it in the right forum.

    I am planning on building a bread oven on my farm, and I would like some feedback before I go ahead and finalize my plans. I'll describe my current plans, but I welcome any advice/warnings about them from those of you who know much more about this than I do.

    Right now I'm basing my design on the one that appears in Bread Builders.

    I want to be able to bake 200 loaves per firing, but I do not plan on baking every day - once or twice a week, at least to start with. I am thinking a 42" x 48" should be about right, but I'm not sure. Since I want to bake quite a bit at a time, I'm planning on putting the insulating cement beneath the regular cement on the hearth slab, in the hopes that the oven will retain enough heat.

    Right now I'm torn about the hearth slab design. I'd prefer not to float it on rebar, but I'm not sure if it will expand and cause cracking if I don't. Some things I've read on this forum suggest it wouldn't.

    Thanks for any help.

  • #2
    Re: General Question

    So, where's the choice?
    Build your oven to the size required with the base as per plans with plenty of efficient insulation on top of your base, then add the extra thermal mass bu stacking your firebricks on their sides rather than on their backs, making it 4 1/2" thick rather than only 3" A double layer of 3" bricks will give you even better thermal mass (but needing much more wood and time to heat up, but lasting much longer).


    Prevention is better than cure, - do it right the first time!

    The more I learn, the more I realise how little I know

    Neillís Pompeiii #1
    Neillís kitchen underway


    • #3
      Re: General Question

      Thanks for the response - maximizing the mass does make a lot of sense. Do you have any thoughts on the necessity of suspending the hearth slab on rebar, or can I safely make the oven monolithic?



      • #4
        Re: General Question

        The Bread Builders design is a great starting point, but it has been proven time and time again that it needs insulation. I was reading in a bread baking book about someone who made one of those ovens and insulated really well; he baked 16 batches off a single firing.

        You should be able to combine the insulating techniques discussed on this forum with the large thermal mass of Bread Builders to make something that can bake large amounts of bread fairly efficiently.
        My Clay Oven build:


        • #5
          Re: General Question

          Hi G!

          Wow! You are a glutton for punishment. 200 loaves is a lot of work! I would assume that would be about 300 pounds of bread. CajunJim will hopefully chime in and give you more info.

          My oven is based on a refactory Casa insert kit on a Scott base. It is one meter in diameter, giving it a hearth footprint of about 8 square feet. I find I can comfortably do about a dozen loaves - about 1.5 to 2 loaves per sq ft. Your 42 x 48 oven would be about 14 sq ft. While I would guess an experienced baker would and could get a higher loading of the oven I would only be able to get about 30 loaves (more if they are oblong) into the oven. I think you really need to be able to do 70 loaves per batch so...it feels small to me given your ambitions.

          As mentioned above, the one weakness of Scott ovens is insulation. I see it in my oven in that with the hearth insulation below the hearth slab, the slab extends beyond the oven to the edge of the base without insulation. I would strongly encourage you to create a heat break around the hearth so that the heat you pump into the hearth does not have any easy way out except back into the oven. The dome insulation is easy. I would follow the basic logic expressed on this site and, given your ambitions, double it as a minimum.

          However, I would suggest seriously considering building a "house" around the dome so you can use lots of loose insulation and have a real roof to shed water and keep the dome and the hearth slab dry. Having an ultra thick oven that is routinely wet from rain/snowmelt would be a real pain.

          Good Luck!


          • #6
            Re: General Question

            With the amount of bread you want to bake I would personally also consider a guillard oven. That way you can easily re-fire between batches if you need to. The obvious downside being the lack of documentation for them compared to the black ovens. They aren't rocket science and some cutaway images come up on google images but nothing like the bread builders plans or the plans offered here.

            This thread links to a video of a guillard oven in use by one of the more storied bakeries in france.


            • #7
              Re: General Question

              Hi G!

              You can do the base pretty much any way you want to. Having s monolithic base will generally mean using more material. Other than involving more material than is necessary it is not a big deal. However, you don't want to simply build a giant cement and/or cinder block base. It will need insulation below (and I think around) the hearth and you should probably put rebar in the hearth slab just to minimize cracking if nothing else. The supended slab that Scott describes works well. Not hard to do.

              Hang in there!


              • #8
                Re: General Question

                I'm a skeptic about the suspended slab. Good masonry practice holds that rebar should be well buried in concrete, at least two inches in. I think the point was some thermal bridging protection if you insulate below the slab: I'm skeptical about that too.

                If you insulate between your support structure and your oven floor, you don't need any of that difficulty. As Neill points out, you can easily add thermal mass by laying your floor bricks on edge, or by putting a thermal slug below the floor. Google "island hearth" for more on this technique.
                My geodesic oven project: part 1, part 2


                • #9
                  Re: General Question

                  I agree with Dmun - rebar should not be exposed. I would build the suspended slab monolithic with the walls and insulate above the suspended slab only (not underneath).


                  • #10
                    Re: General Question

                    I believe that there are plenty of ovens out there that follow the Allen Scott design. Here is a thread that you can look at that provides numerous oven builds per the Allen Scott method.Frankie G's Wood-Fired Pizza Oven