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Creating a form for a cast oven

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  • Creating a form for a cast oven

    I'm working on a one piece cast oven and I had some trouble finding good pictures documenting the construction of the mold.

    Here are some step by step photos.

    First picture is the layout. I used an inside diameter of 32", used one sheet of plywood to create the outer and inner form curves. I chose to ad the door into the form for ease of construction
    you can see in the next two photos what that looks like. repeat on a second piece of plywood to create two of each.

    discard the middle section or play hula hoop

    Next step was to build some risers of the appropriate height. I chose a stem wall 6" tall on the inside so the risers are 4.5" with 3/4" plywood top and bottom.
    Last edited by reubenandrena; 06-18-2014, 06:08 PM.

  • #2
    Re: Creating a form for a cast oven

    I'm using 1/8" masonite hardboard I purchased at home depot with the shiny side facing the concrete.

    you can see in the pictures that I wrapped the external form and then followed the same steps for the internal form
    Last edited by reubenandrena; 06-19-2014, 02:47 PM.

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    • #3
      Re: Creating a form for a cast oven

      on the internal form I forgot to account for my tapered door opening at the earlier stage of layout so I got to do some quick fix hack work.

      in the second photo you can see the new layout lines I need to cut to create the taper.

      wrapping the door with masonite required a paper template to account for the curve. the template looked somewhat like a banana when flattened out for tracing.
      Last edited by reubenandrena; 06-19-2014, 02:49 PM.

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      • #4
        Re: Creating a form for a cast oven

        at this point you can see the masonite attached to the door archway. I debated cutting the sides as separate pieces but opted to be lazy and just snap it around the bend.

        The last two photos show the forms assembled on top of a piece of 3/4" plywood.

        I measured the gap all around to make sure it was even and then fastened both forms to the plywood with a couple of screws.

        I created a template that screwed onto the front of the arch to act as damn to keep the concrete in the form and also as a screed template for the top of the arch.
        Last edited by reubenandrena; 06-19-2014, 02:52 PM.

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        • #5
          Re: Creating a form for a cast oven

          endgame now. I covered over the hole I cut in the inside form (this was to provide access to screw down the inner form to the plywood base) with a scrap of plywood.

          I drew a radius on a scrap of pine to act as the screed guide for the sand dome.

          pack on the sand and then screed it off to create a smooth inner profile.

          incidentally I simply raised this screed up when placing the concrete to act as a screed during the pour.
          Last edited by reubenandrena; 06-19-2014, 02:55 PM.

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          • #6
            Re: Creating a form for a cast oven

            Last step is to cover the sand with wet strips of newsprint.

            I sprayed everything down with a can of spray vegetable oil for coating the frying pan before filling with concrete.



            I hope this can help anyone else attempting this project in making their templates and forms.

            In speaking to a local masonry company they told me that they use foam board and carve out the dome shape with wood tools instead of sand. they build larger fixed in place pizza ovens using firebrick and a one piece cast dome for the top. this would be a good alternative topper instead of using the sand.

            epilogue... cast my oven using plibrico plicast 27 from french services in baltimore MD. very nice people to deal with.The oven came out of the form nicely. I used 7 55lb bags with a final wall thickness of 2.5"

            reuben flax
            Last edited by reubenandrena; 06-19-2014, 03:04 PM.

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            • #7
              Re: Creating a form for a cast oven

              I'm building another oven and I wanted to show pictures of how I wrap the oven with three layers of insulation. each layer is draped over the oven and cut to create pleats that close up to conform to the shape. I use steel wire bent into U shaped pins to help hold the pleats closed and in place as I apply each layer of insulation. There are a total of three layers applied in alternating directions to stagger the seams. I make the pins long enough to go through all three layers to help keep everything in place.

              This gets covered in a metal lath shell and then stucco

              reuben
              Last edited by reubenandrena; 12-27-2014, 06:55 PM.

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              • #8
                Re: Creating a form for a cast oven

                Looks good do you have a pic of the oven pre wrapped?

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                • #9
                  Re: Creating a form for a cast oven

                  This is a picture of the oven dome before I covered it with insulation. you can see areas on the outside of the oven where I had to cut off some concrete that had drooped over the form. also in the throat of the oven you can see my door rabbet cast into place to help seat the door. the oven is sitting on a double layer of firebrick... insulated on bottom and dense above them.
                  Last edited by reubenandrena; 12-27-2014, 07:50 PM.

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                  • #10
                    Re: Creating a form for a cast oven

                    I know it's too late for you now, but it is far simpler, quicker and easier to cast the oven in place by making a sand dome as your mould for the whole dome, create some removable form work in front of it for the entry, then when you have placed the casting material over it, simply remove the sand. Doing it this way eliminates the need to both create inner and outer formwork as well as lifting a very heavy casting and relocating it. The castable will stand up vertically against the sand form ok if you get the consistency of the mix right.

                    If the casting has to be moved, three steel loops cast into the top make lifting easier than prising a bar under the casting which can create damage.
                    Last edited by david s; 04-16-2015, 12:32 AM.
                    Kindled with zeal and fired with passion.

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