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Thermal mass

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  • Thermal mass

    This message was directed to Mr. James, but help from anybody will be highly appreciated


    Please, I need some help here.
    In the last days I had been carefully reading a lot of messages about oven/thermal mass try to picture some doubts that are following:
    I am a pizza lover and an oven home builder, who wants to fire occasionally (weekly or so).
    Since my intentions are to be a weekend pizza maker and eventually a bread cook I think that spend 3 or 4 hours to get the necessary temperature could not be a great deal.
    My oven will be 34?x 26? barrel vault or 32? igloo shape (reading about the your mass answers in the yahoo/brick-oven forum I am now pretty sure that I need to go with an Pompeii oven ceiling)
    I had build the firebricks hearth above a slab of 2? vermiculite/cement isolation + 3 1/2 ? concrete mixture + 11/2? cement/sand/lime level surface ? this means 2? isolation + 5? thermal mass -. The firebricks of the hearth were setted on the edge (41/2?).
    I am wondering now that this could be to much thermal mass, but at this time it will be difficult to rebuild the base again.
    1) Could I to remove and set the hearth firebricks on their side? Do I have any advantage doing this? (Does you know how the firebricks set could affect growing/dropping of internal oven temperature and cooks characteristics?)
    2) Could I finish the internal body of the oven using the actual base and go to the oven ceiling (firebricks on the edge) with a little as 2? cladding mass (+ vermiculite isolation) over it?
    3) Could the thermal mass difference (5? below the base against 2? above the ceiling) affect the pizza/bread cooking characteristics?

    Otherwise, the isolation + concrete base were pouring inside (in-between) the walls without gap between walls and hearth base,
    4) may I use this kind of arrangement, or do I need to rebuilt (please, do not confirm this!) this base?

    I intend to finish the oven body still this week and I hope to go with the right proportions.

    Any help will be greatly appreciated.

    Thank you.

  • #2
    Hi Luis,

    I think a lot of folks have this question.

    You do not need anything more than a half-brick of mass in the dome -- about 4 1/2". Virtually every pizza oven in Italy has between 2" and 4 1/2" of dome mass, including commercial ovens in pizzerias. The typical handmade brick oven has a firebrick cut in half with the cut side facing out, giving you a 4"-4 1/2" thick dome, or a brick on its flat side, giving you a 2"-2 1/2" thick dome.

    You do not need any additional mortar on a 4 1/2" dome. Experience shows that the entire mass of a 4 1/2" dome is almost never fully heated, so any additional mass is actually very negative and wicks heat away from the inside of the oven.

    On the floor, you should definitely put the bricks on the flat side, giving you a 2" floor. Anything more than that is much too much. A 4 1/2" oven floor will never heat all the away through, which will result in heat wicking away from the inside of your oven the entire time you are cooking -- which is not good. A 2" floor on a 2" thermal hearth layer will retain enough heat to cook bread, will get hot for pizza, and will easily meet your requirements.

    I think the Breadbuilders oven is pretty confused as to what it wants to be (commercial bread oven vs. home pizza oven), and don't think it works well as a home brick oven.

    I hope this is all helpful.

    Also, check the "why round" posting.

    Pizza Ovens
    Outdoor Fireplaces


    • #3
      I went into some detail responding to this on the Yahoo brick-oven group. Please check that out and I think you'll get all the info you need.