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Please comment on kit design - Forno Bravo Forum: The Wood-Fired Oven Community



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Please comment on kit design

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  • Please comment on kit design

    Hi, I've been working towards the barrel vault design in the bread builders book. I'm now up at slab height and I've decided to go with an igloo style kit. The design in my book as for 2" vermiculite/concrete underneath a 3.5" concrete slab in which sits a firebrick hearth. The refractory where I'm buying the kit tells me that the base is 50mm thick(fireclay I think) and to sit this on 2" vermiculite concrete. My questions are
    1. Will this 50mm thick base have enough thermal mass or should I add maybe an inch of concrete underneath it?
    2. I intend building the chimney out of red brick instead of firebrick to save money. Is this a good or bad idea?



  • #2
    Re: Please comment on kit design

    Hi Richard, I was a bit confused by your description. If your intent is to sit the 50mm base on top of insulation, then yes, my opinion is that 50mm is enough thermal mass unless you want to do some serious long term cooking with one burn.

    If your intent is to use 2" vermiculite concrete as your insulation layer then my strong recommendation would be either:
    - use insulating board (either Calcium Silicate or Ceramic Fiber) - this is a much better insulator than Vermicrete
    - use a much thicker vermiculite/concrete layer (4" minimum)

    Good luck!


    • #3
      Re: Please comment on kit design

      Thanks Neil, I'll have to look for info on the other materials you recommend, I hadn't considered anything but vermicrete. Have you any comments on using standard red brick for the entrance and chimney?


      • #4
        Re: Please comment on kit design

        Hi Richard

        there are many people on this forum way more experienced than me so hopefully you get some responses other than mine! Maybe you should post in a more visible area of the forum?

        In any case, I suspect you will get a wide range of responses on the standard brick versus firebrick question. There are some pizza oven companies that say it is OK to build the dome out of standard brick (most people here would disagree with that).

        The chimney is going to get extremely hot but not as hot as the floor or the roof of the dome. I think you will be OK with standard brick for the chimney as long as the quality of the bricks is good. Here in California standard bricks cost 50 cents each and firebrick costs $1.50, so I don't save much by using a few more firebrick. I will be making my lower chimney out of firebrick and then transitioning to stainless steel vent pipe.


        my build is here:



        • #5
          Re: Please comment on kit design

          I'm sure Neil is right ....depends on the standard of the brick. My entry and chimney is mixture of many brick and pavers and is doing well 2 years on. Firebrick cost nearly $4 each here and let's face it they are pretty bland to look at.
          Regards dave
          Measure twice
          Cut once
          Fit in position with largest hammer

          My Build
          My Door


          • #6
            Re: Please comment on kit design

            Thanks guys, I'm just basing my idea on a belief that the chimney area isn't relied upon to retain heat? The kit I intend using has a 3 section vermicrete tunnel with a hole in the top for the chimney. This is then finished with thin firebrick slips I believe. Some pics here Wood Fired Pizza Oven Parts and Accesories to build your own wood fired oven . I was thinking it looked kind of ugly but my wife actually wants the oven and chimney to have a plastered finish so I might just go with the kit 3 piece chimney. I started digging a hole in the ground just over a year ago. I poured the base slab eventually last December and I now am ready for the hearth structure. If I go for the kit my wife will return from work some day 'soon' and the oven will be sitting there, and my life will get easier can't actually blame her with the current rate of progress + I've grand plans for an all weather outdoor BBQ area where I can brew beer also.




            • #7
              Re: Please comment on kit design

              The smaller oven with the flue exit inside the oven chamber is not such a good design. It works on an updraft principle and does not give such good circulation as the flame simply wants to find its way to the flue as fast as possible. Retaining heat in the chamber is also more difficult with this design. The larger oven employs a flue exit at the front and independant of the oven chamber giving you a cross draft, utilizing all of the flame and providing good circulation. The better choice IMO.
              Kindled with zeal and fired with passion.


              • #8
                Re: Please comment on kit design

                Thx Dave, yes, the one im going for has the flue over the 'entrance arch' rather than over the oven. I can't remember the exact dimensions but it fits on my 1.6metre x 1.4metre slab with a small amount of space to spare