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Vermiculite exercise ball questions

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  • Vermiculite exercise ball questions

    I'm planning a WFO build. I've been acquiring materials and so far have;

    65cm exercise ball
    25 1-1/4" fire bricks
    sack of Thermobond 915 refractory cement
    1" thick ceramic fire blanket
    all the wood+mold making supplies

    I'm having trouble finding vermiculite. The closest I've come is a product labeled as Therm-O-Rock Pool Base. It is vermiculite but I have a feeling it might be a pre-mix that already has some portland in it. Not sure if this will be a problem???

    So, I want to do the few inches of vermiculite concrete over the ball, then insulation blanket, chicken wire and a few coats of render. The twist is that I need to complete the dome to actual outer dimensions (not planned haha) before I lay out and cast the base as I want to create a 3" thick vermiculite/concrete base with the firebricks set into it. I have decided I want/need the walls of the oven to be flush with the base perimeter.

    Can I build the dome completely (with blanket and render), mortar it to the finished base and then cure it? Or do I for sure need to fire cure the initial concrete/vermiculite shell first. I ask because I want to complete this in the garage in the dead of winter and trying to cure a bottomless shell with fire might be an adventure.

    I've included a photo I stole from sandrine on The Owner Builder Network to illustrate how I want to create the base after I have the exact outer profile of my completed dome.


  • #2
    Hi Export,

    Welcome to the forum. Imo the infamous vermiculite/ exercise videos on youtube have gotten a lot of air time and have lead many astray. To make a long reply short, my advise is to download the forno bravo Pompeii brick oven plans. There are also many castable oven builds on this site that yeild a much better result than what you ae intending to build.
    Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build


    • #3
      Vermiculite concrete is an insulating layer, not a refractory layer. Building your dome out of vermiculite is not going to give you the sort of thermal performance you want out of a pizza oven. You need to use firebrick or refractory concrete. Then you can use the vermiculite over that as insulation
      My build progress
      My WFO Journal on Facebook
      My dome spreadsheet calculator


      • #4
        Thanks DJ, deejayoh for the more detailed reply. I was a little short on time last evening. I hope that some of those who chose this route will also respond.

        export! , The problem with the youtube videos conserning the infamous gym ball/medicine ball/excersize ball/vermicree/perlite dome builds is that there are not many follow ups on just how well they perform after time. Some are enquiring on how to recover from that choice. Here are some links that may help you on your choice.

        Outer Layer Wood Fired Oven

        Using Refractory Mortar to skin Vermicrete dome

        Barrel/Vault Build in AZ

        How I build my perlite/cement pizza oven with gymball

        Feedback from Perlite/Cement oven owners?

        Smoke leakage vermiculite gym ball cast

        Perlite/Cement/Grog Dome

        Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build


        • #5
          Thanks guys. Will continue reading.

          Basically I'd like to give the whole outdoor oven idea a whirl and see if i'd like to maybe build a "real" one in the future. I've done tons of masonry and tile work and the skill set doesn't concern me.

          Being in Canada, I'd like to build this simple version in my garage over the next few months and then carefully transfer it out to it's perch at first thaw and start curing immediately. I'm not independently wealthy but I figure I can risk a few hundred to try it out and salvage all the firebricks from the floor if I take a hammer to it.

          I figure with the lack of spare time in the warm weather I'd be curing a Pompeii oven in the fall of 2020 or spring of 2021!!

          I fully understand that I'll lack the thermal mass of a firebrick/refractory dome but it appears you can keep enough of a fire going in a lesser oven to hit the 90sec mark and have some fun working on your dough skills.


          • #6
            When I am successfully elected Prime Minister (I'm an Australian, I can't be any worse than the last 5 or 6 we've had) even posting a video about vermiculite and exercise balls will be illegal.
            Only murder and rape will attract a longer sentence.