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Ithaca Oven 2nd attempt - Forno Bravo Forum: The Wood-Fired Oven Community



I'm Peter Reinhart! Ask Me Anything! Monday, February 15, 2016 7:00-8:00 pm EST

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Ithaca Oven 2nd attempt

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  • Ithaca Oven 2nd attempt

    I've got some in-process pictures of my 2nd attempt at a rectangular style oven.

    On my 1st oven i used only standard mortar for the entire thing. It was an identical design as the oven shown here, but slightly smaller. I didn't interlock the side walls with the front or back on that one, and it collapsed after about 1/2 dozen pizzas.

    For budgetary reasons i decided to use heatstop50 for the arched roof, and upper parts of the front and back walls. And normal pre-mixed mortar for the remainder of the oven. I used red clay bricks for everything but the floor where I used fire bricks.

    I'm worried for obvious reasons about the structural stability of this design. I layed the bricks the "thin" way which makes me even more concerned. Should I add a cladding to this for strength? Any other input?

  • #2
    Re: Ithaca Oven 2nd attempt

    Have you downloaded the Pompeii plans from FB. They are free and though you are not building a Pompeii style oven, many of the principles carry over to barrel vault type ovens.
    Questions: 1. do you have any insulation under the floor? 2. What makes you think that conventional mortar is going to hold up this time?

    I would stop where you are, take the part of the oven that is done with Heatstop apart from the rest, set it on the ground gently, and rebuild with the homebrew hi temperature mortar, then carefully lift the top back on and remortar it. The homebrew hi temp mortar is made with: sand, lime, fireclay, and portland cement, mixed in a ratio of 3:1:1:1. For the cost of 1 bag of Heatstop, you can make enough mortar to build you entire oven and it will not fall apart when it gets up to pizza temperature.

    Good luck,



    • #3
      Re: Ithaca Oven 2nd attempt

      I have just a 2-1/2" enclosed air gap under the fire brick floor. I am thinking that depending on how the oven performs, I will attach further insulation to the underside of my air gap as needed

      It isn't that I think the normal mortar will work, just that it won't cause the oven to collapse this time. Because it is only in the vertical walls, a crack will not cause as serious of problems.

      I would have made the entire oven from homebrew refractory but fireclay is apparently not available in NY state? according to my block supplier.

      The majority of my concern comes from the way I laid the bricks, and my masonry ability in general.


      • #4
        Re: Ithaca Oven 2nd attempt

        Part of the problem is the joint size, it is too big, and the bigger it is, the quicker it will burn out. Secondly, the side walls need to be buttressed somehow or it will collapse again. Cladding will help, but is probably not enough alone.


        • #5
          Re: Ithaca Oven 2nd attempt

          I have 2-1/2" air gap under the hardiebacker cement board, under the fire brick floor.

          I don't think the standard mortar will hold up better this time, but I decided it was acceptable to use it in areas that were less critical. The side walls should be under a purely compressive load and should hold up even with cracks.

          How would I buttress the side walls? Another layer of bricks?


          • #6
            Re: Ithaca Oven 2nd attempt

            No, the walls will be pushed outward by the arch. Another layer of bricks would probably do it.


            • #7
              Re: Ithaca Oven 2nd attempt

              I was able to remove the form last night, and patch up all the joints that were missing any mortar. What a satisfying experience! Every ounce of mortar filled in these roof joints is helping greatly. It looked pretty fragile standing without the front and back walls.... yikes!

              I then finished the front and back walls. It looks great, better than the last oven that was constructed in below allowable temperatures and was already showing cracks at this point.

              In lieu of a second layer of bricks to buttress the side walls, I am strapping the walls together with 2 angle iron bars, one along the top wall brick-roof joint on each side. They will be pulled together using threaded rods running along the front and back of the oven. I will tension these, and be watching for loosey-gooseyness as i begin the curing process.

              The chimney issue that was pointed out to me on my accidental 2nd posting of this thread has not been remedied yet. I misunderstood the position of the chimney entrance from the oven, and my chimney will suck heat straight out from the top of the dome. I will either extend this chimney down into the oven, or I will patch it up and build a proper front on.

              Thanks for all the input up to this point!


              • #8
                Re: Ithaca Oven 2nd attempt

                That should work as buttressing. I think the arch when I stripped the form was the oven at it's loveliest.

                As I finished mine out, I ended up standing on top of and stacking brick and mortar on top for a 2 week period with no problems, and I am not a lithe figure.


                • #9
                  Re: Ithaca Oven 2nd attempt

                  ALRIGHT! some positive feedback! ahaha

                  I hope my buttressing idea will work, I plan to lay mortar under the straps, and just tighten it enough to hold it on until the mortar sets. Then i will tighten it more before i begin the curing process. This will give me a nice and evenly distributed "squeeze" on the oven.

                  With the metal getting quite hot, I wonder if it will give up a little. I'm going to be keeping an eye on this continuously while curing and cooking. If needs be i will tighten it down more. I worry once it cools though, it may become overly tight? I guess this is getting fairly far from a newbie forum post, and more on to a "how to fix an incorrectly/cheaply built oven so it will make pizzas for your hungry friends"

                  Thanks again


                  • #10
                    Re: Ithaca Oven 2nd attempt

                    We have fired and cooked pizzas in the oven probably 6 times now. There was some fairly serious cracking that developed during the 1st few firings. It hasn't spread or worsened since then, so I'm feeling a LOT better about it. I think I'll "point" the cracks and then clad the whole thing in another 1/2-1" of cement of some kind.

                    The outside has been getting to 500ish F and the inside has been an error reading on my IR thermometer (650+). Pizzas have been delicious but I still need to make my chimney extend down into the oven, and work on some type of tunnel entrance to control the smoke better. I've been plugging the chimney with Roxul stone wool insulation to keep the heat in while cooking.

                    Will vermiculite cement work for a cladding layer?


                    • #11
                      Re: Ithaca Oven 2nd attempt

                      Vermiculite mixed with portland cement at 6:1 will give you excellent insulation. Congratulations on getting your oven done and cooking pizza.