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Metal dome lining design

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  • Metal dome lining design

    Hi, all. Lots of good info in this forum, very helpful.

    I am getting ready to build a pizza/bread oven and am contemplating an idea I haven’t seen anything about. Perhaps someone has experience, or at least thoughts, about it.

    My materials are mostly local and recycled. I’ve built a base from old blocks and gravel fill, topped with glass bottles set in a perlite and clay mix for the hearth insulation layer. On top of that is a clay/sand thermal hearth. I live in “Steel City” (Gary, Indiana) so there is industrial-sized fire brick available, and I got an 18” x 24” x 3” piece for the main floor (for $1!), with some smaller pieces to surround it. That way I have no issue with seams or uneven heating on the cooking surface. Then I have standard fire bricks for the wall (4.5 x 9 x 2.5), in a vertical placement. The thermal mass dome will be a 3” clay/sand mix (1:3), then a 5” layer of insulation (either clay/straw or clay/perlite), and an outer render layer.

    I want a 16” interior height and happen to have a fire pit lid which is 7” high. It is thin steel (painted black) and 19” in diameter. I’m thinking this would be a good interior dome liner - better heat reflection during live fire pizza cooking, no spalling over the cooking area, better strength for the open span and easier construction. But this is where I am not sure of my design. The metal lid sitting on the vertical bricks makes the maximum height 16” as desired, but my plan is for the interior diameter to be 22” wide and 25” long (slightly oval shaped). So the lid would only be partially set on the wall bricks (at the rear wall). The rest would be held in place by the clay thermal mass, around the edge and against the metal. There’s a handle on top which will be embedded in the clay to help secure it. I could add some other anchors around the metal lid as well if necessary.

    Will the metal/clay interface be a problem from different thermal expansion? Is there anything I am missing in this design?
    Another potential issue is that after a test fire I found that the clay doesn’t stick well to the metal or bricks (maybe they are too smooth). But after it is fully built I don’t think that will cause problems. Might even prevent some thermal expansion stress.

    I’ve included a photo of a quick mock-up I made, with a reduced diameter to see if the extra few inches were essential (they are). And after a test run I will probably add a front chimney as well - too much smoke in my eyes!

    Any advice or suggestions would be greatly appreciated.

  • #2
    I have something like this setup as an experiment. It is a throwaway design, mortarless box made from bricks with and inverted iron wok inside the box. The floor has inch thick firebrick and the dome sits on 3 bricks inside the brick box. I have not gotten it to work with firewood , the air flow is a mess and it smokes too much, I am using a gas burner to make pizza, it's kind of like a big black egg design.

    The thermal expansion may not be such a big issue as the dome is one piece and the semi sphere design means it should expand evenly and minimally, like the whole circle increasing in diameter slightly. So worst case, you might just end up with minor cracks where the dome sits on the bricks & you could just coat over the cracks with some homebrew.

    Watching this build closely. best of luck !