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help with making a dome.

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  • help with making a dome.

    -i made a base for the oven:
    cinder block, 3/4" steel plate top, then 3 inches concrete over that.
    i have a layer of fire bricks for the oven floor.
    i plan on making the first level of the oven with firebricks on ends(going verticle) with a homemade dome on top of that.

    my question is with the dome. would anyone see any problems with making a dome out of refrax mix using a metal oven top as a form? I have a dome shaped oven top, similar to a basic weber type chargoal grill but not as high. I plan on coving that with newspaper, which can be removed, or burned off later. then just cover the dome with refrax mix and rebarb. I also plan on leaving a hole for the chimney on one side. i thought after i get a thin layer, i would place thin nails in the refrax to gage the thickness all around the dome.
    does this sound feasible? has anyone else used this technique? finally how thick should it be? I haven't decided how I will finish the top yet. I'll either build a block base around and cover inside with vermiculite, or just cement over the entire thing. I'll worry about that later though. I'm just concerned with the dome top now.
    Thanks, Aaron

  • #2
    Re: help with making a dome.

    Hi Arron,

    Sounds like you have a good sturdy base for your oven.

    Be sure to insulate between your steel plate / cement base, and your fire brick cooking floor. If you leave out the insulation here there is enough thermal mass involved with the cement base it will take a big fire a very long time to heat up your oven floor enough to cook hot food.

    You may also want to consider laying your fire brick flat for the oven floor. I have found the 2 inches of fire brick thickness provides enough stored heat to cook for a couple days after a pizza fire. More thickness will hold more heat and last longer, but it will also require more fire, over a longer period of time to get the floor hot enough to cook food.

    I don't have experience with the formed dome, so won't venture an opinion on that issue.

    Good luck with your build, and do send along a couple photo's now and again!

    JED

    Comment


    • #3
      Re: help with making a dome.

      In Ohio, you're going to find that refractory concrete is twice as expensive a material as firebrick. The folks who are casting refractory concrete domes are in places like Australia, where a firebrick costs three bucks, for reasons best known to the folks down under.

      And your metal dome form: how you going to get it out? Cobb ovens were traditionally made with green wood lath forms, that could be burned out after the oven was dry. They also had a little "give" to them so they would deform as the dome shrunk.

      I second Jed's advice to insulate under your floor. 'Insulate! Insulate! Insulate!' is our motto.
      My geodesic oven project: part 1, part 2

      Comment


      • #4
        Re: help with making a dome.

        You don't want to use rebar cast inside of a refractory dome. The differences in expansion rates will most certainly cause severe cracking. If you want to add anything, use stainless steel needles, but if you use the right product for the job, even the needles would not be necessary. The right product being CASTABLE refractory concrete.

        I also have reservations about the steel oven dome. You mention it is similar to the lid of a Weber grill, that would be a pretty light gauge steel....I don't think it would hold up very long. If you are merely using it as a form and plan to lift the dome off of it after it sets up.....you may want to enlist the help of the entire neighborhood or rent a crane, a single piece cast dome is gonna be REALLY heavy.

        RT

        Comment


        • #5
          Re: help with making a dome.

          the metal dome is just used for the shape. I plan on putting newspaper over the metal dome and then refrax mix over the newspaper, which would keep it from sticking to the metal. Then just burn off the newspaper. As far as the rebar, coincidentally what i planned to use are 1/4" stainless steel dowels I had laying around the house. I don't know what there from but I've been using them for tomato stakes. I plan on bending 6 of them around the shape of the metal dome and placing them like Longitude lines on a globe.

          I haven't begun to look for refrax mix yet. Is that going to be difficult to find in ohio? any fellow buckeyes that have had luck finding it? is refrax mix not castable?
          Thanks for the help,
          Aaron

          Comment


          • #6
            Re: help with making a dome.

            Refrax is Forno Bravo's brand of refractory mortar, it's made for putting firebricks together. It's expensive, as is heatstop and other refractory products. There are specific refractory products made for casting, usually reinforced with stainless steel needles. Your local refractory dealer will have all this stuff. Harbison-Walker is the big national brand, they have outlets in most industrial cities, and there are other refractory dealers as well. Google maps is a good place to start: start with a search for "refractory near columbus ohio" and start making phone calls.
            My geodesic oven project: part 1, part 2

            Comment


            • #7
              Re: help with making a dome.

              I and a couple other guys here have used sand as a mold for the dome, it is easy to remove after the refractory is set. I also found castable concrete mix for $19 for a 50 lb bag. do a search for "castable" here and you will find a ton of info on this.
              good luck and let us now how you progress....oh and pictures pictures pictures...

              Comment


              • #8
                Re: help with making a dome.

                thanks guys. I'll follow up with some pics when I finally get started. This has been an on again, off again project for a few years now.

                Comment


                • #9
                  Re: help with making a dome.

                  First off, I want to say that I have no experience with making a pizza oven or any mortar/concrete work in general. With that being said, what if you, Aaron, made a thin layer of your dome, enough to hold its shape when cured and lifted, but not too heavy. Use the oven lid or anything else that you think would work as the template. Place this thin cast onto your oven base, then complete the dome to your desired thickness with it in place. This will prevent you from having to get an engine hoist to put the dome in place.

                  I don't know if this will work since there will now be two layers of your casting material that cured at different times and under different conditions, but it's the first thing that came to mind.

                  I'm doing some research now to hopefully build an oven in the future and I was trying to come up with some way of getting the dome shape when I came across your post. I hope it works, and would love to see the results.

                  Comment


                  • #10
                    Re: help with making a dome.

                    i had those same concerns with it drying and then adding another 2 inches of thickness. What does everyone else think?

                    Comment


                    • #11
                      Re: help with making a dome.

                      i think moisture from the first layer should be cured out before applying the thicker second layer. Just a guess but I think moisture from the first layer may get trapped between the two.

                      Comment


                      • #12
                        Re: help with making a dome.

                        I would discount any advice on the use of refractory concrete from anyone who hadn't already used it, myself included. That said, I think any plan to move a thin shell of castable is doomed to failure.

                        This thread may yield some answers:

                        http://www.fornobravo.com/forum/f43/...uild-7866.html
                        My geodesic oven project: part 1, part 2

                        Comment


                        • #13
                          Re: help with making a dome.

                          Originally posted by aaron4osu View Post
                          -i made a base for the oven:
                          cinder block, 3/4" steel plate top, then 3 inches concrete over that.
                          i have a layer of fire bricks for the oven floor.
                          i plan on making the first level of the oven with firebricks on ends(going verticle) with a homemade dome on top of that.

                          my question is with the dome. would anyone see any problems with making a dome out of refrax mix using a metal oven top as a form? I have a dome shaped oven top, similar to a basic weber type chargoal grill but not as high. I plan on coving that with newspaper, which can be removed, or burned off later. then just cover the dome with refrax mix and rebarb. I also plan on leaving a hole for the chimney on one side. i thought after i get a thin layer, i would place thin nails in the refrax to gage the thickness all around the dome.
                          does this sound feasible? has anyone else used this technique? finally how thick should it be? I haven't decided how I will finish the top yet. I'll either build a block base around and cover inside with vermiculite, or just cement over the entire thing. I'll worry about that later though. I'm just concerned with the dome top now.
                          Thanks, Aaron
                          Hello Aaron

                          It seems like you are causing yourself a lot of heartache in how to deal with the metal form you are using to create your dome. If you are going to take on the task of building a wood-oven, then, perhaps you should consider using some other type of form before commencing the dome. There are many types available which can be easaly burned off in the first gentle firing. Myself, I used 12 pieces of cardboard (bought from my local re-cycling agency for £3) cut into half-moon shapes measuring 1 meter in diameter by 50 cms in height. These were interlocked into each other making 24 ribs of cardboard held in place with strips of newspaper dipped in a flour and water mix. This sounds very primative but........it worked. The form was as strong as an ox and as light as a feather and just easaly burned away in the first gentle firing.......and cost £3.27p including the flour!!!!

                          Whichever method you choose, I wish you the best of luck with your project. Oh......and don't forget to take lots of pics along the way, I look forward to seeing them.

                          Regards Terry (C.F)
                          Honi soit qui mal y pense

                          My 2nd Pompeii build.....

                          http://www.fornobravo.com/forum/memb...eii-build.html

                          Comment


                          • #14
                            Re: help with making a dome.

                            Hi Arron and welcome to the forum
                            the metal dome is just used for the shape
                            You could slice your dome into 3 or 4 pieces... Put it back together with duct tape, then pull out each section seperately after your refractory cement cures... You of course would have to build an outter ring of masonite or 1/4 plywood (well supported) to hold the cement around the dome,, Things to keep in mind, where is your door/chimney going etc,

                            Cheers
                            Mark

                            Comment


                            • #15
                              Re: help with making a dome.

                              "The differences in expansion rates will most certainly cause severe cracking. "

                              I agree with RT. I would avoid using rebar or mesh in the dome. Also, the dome should be cast monolithicly. Successive thin layers will not bond to each other with anywhere near the strength of a full depth pour.

                              Have you considered casting in segments (similar to the Forno Bravo precast units) ?

                              Comment

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