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Earthenware geodesic oven? - Forno Bravo Forum: The Wood-Fired Oven Community



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Earthenware geodesic oven?

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  • Earthenware geodesic oven?

    Hi All,

    A quick intro - I've been lurking here a while, and have been inspired by the quality of work I've seen here. Thank you everyone for sharing - I've learnt a lot from this forum. I originally wanted to build a Scott type oven, and then swung completely the other way (once I found out how much the firebrick would cost me!) and planned a basic mud oven as per the Kiko Denzer book. And then I found this site...

    I've been really impressed with the geodesic designs I've seen on the forum, and a comment by edschmidt on dmun's geodesic build thread set me thinking....

    You know I do have a kiln, I could fill my molds with earthware clay which is fired to cone 8-10 2000-2300 deg. and has a high shock resistance. It obviously can tolerate high temps, and costs approx. 34 cents per pound. The triangles would easily fit into the kiln and the density is comparable with firebrick. Can you see any downsides?
    I'm seriously considering doing this - building a mould and using clay to produce the triangles for a geodesic oven. I don't have a kiln though...

    My question - although to me this seems like a great idea, will it work? Will the earthenware clay stand the thermal shock of the fire? Although I don't have a kiln, surely I could build a rough & ready effort out of old bricks in the garden just to fire the triangles? Could I even fire them in situ - i.e. assemble them after drying, then fire them by having a big fire in the dome? Or would the shrinkage make the whole lot collapse? Please - if you can shoot this down before I waste time on it, I'd be very grateful!

    Thank you all for everything you've shared so far, and for the inspiration.


  • #2
    Re: Earthenware geodesic oven?


    I'm no expert on kilns, but I do know something about early brick kilns, the kind that were made to fire house bricks in situ out of local clay. The bricks nearest the kiln center were the hardest and used for exterior purposes. Those on the outside rings were the softest and used for interior walls. The problem you would be facing is this, plus the fact that you need really high temps for a successful firing of what you want. You might end up with an uneven result and a lot of waste. Just a thought.

    "Made are tools, and born are hands"--William Blake, 1757-1827


    • #3
      Re: Earthenware geodesic oven?

      Well if you are going to make your own clay why not encorporate enough aluminum oxide to make it refractory clay? If you were really cheap, you could snarf up used aluminum oxide grinding wheels (shops toss them when they loose about 10 percent of their rim), smash them up, sift them, and use that for your grit, mixed with your kaolin or whatever. I can't imagine that you can't buy the stuff by the bag from the same place that sells your ceramic supplies.

      The short answer is that, yes, you can make it out of terra cotta, or whatever, just as you can make an oven out of regular red brick, but it will be subject to spalling and cracking. I think if you built a "house" enclosure and kept it absolutely permanently dry you'd be ok.

      The real cost of your oven is your time. I'd say spend as much in materials as you need to make your time worthwhile.

      That said, I'd love to see a molded clay element geodesic oven. It would look so much classier than refractory concrete. you could cast a decorative design in each tile.

      With all this 1800 degree f. high tech insulation, don't think it hasn't occured to me that you could take this sucker up to orange heat for ceramics. Hell, with a blower you could probably smelt iron, but not if you wanted to keep cooking pizza.
      My geodesic oven project: part 1, part 2


      • #4
        Re: Earthenware geodesic oven?

        Ive been working on this and done quite a bit of firing/expiramenting with firing different clay products (I do have a kiln) and come up with the conclusion that while earthware clay does have the thermal shock resistance you are looking for it lacks the thermal cycling resistance. Thats the bad news. The good news is you can get fireclay at the same price or cheaper. Firebricks are actually fireclay and grog which consists of ground up firebricks. Also since fireclay has approx. a 26% aluminum content its got you covered there too. As far as getting firebrick to crush I would check with a refractory sales place in the area and offer to purchase their brocken bricks at a sincere discount. Technically though for full benifit these should be brought to at least cone 5 (1850 deg. I believe.
        Hope this helps.


        • #5
          Re: Earthenware geodesic oven?

          This interests me as I am nearing the time to cast my vent. I have a lot of firebrick dust, a load of firebrick offcuts, a bag and a half of refmix and some newly acquired stainless rods which I plan on using as rebar...

          I know I have taken your problem and aligned it with mine, but i feel like the answers will subdue our collective anxiety about casting refractory on the cheap.. Have you considered an armitutre, or reinforced triangles? is stainless steel the way to go when reinforcing refractory? Did anyone see the article in the new Popular Science about the guy making bricks from pot ash? Is reinforced refmix not strong enough to make geodesic pieces from? Dmun, are you mad at me? I feel like you may have taken one of my previous posts the wrong way. I love you bro... Listen, Im a little drunk, I just fell in love, and it's the most painful thing Ive ever dealt with, and I may be rambling here, but I love you guys... No, really... Seriously.. I love you guys... Really.. Everyone thinks I'll never finish my oven, but you all believe in me right?... Women... What do they know about castable refractories... I'll show em.. Them, and bloody Nancy Silverton, and the Utah Jazz, and...


          • #6
            Re: Earthenware geodesic oven?

            I love you too, Nick. Don't take anything too seriously. If the world were designed the way I would design it for my self, it'd be a small, boring, (but mechanically exquisite) place. And there would be precious little place for exposed concrete.
            My geodesic oven project: part 1, part 2


            • #7
              Re: Earthenware geodesic oven?

              Thanks for all the replies - I can't help thinking I'd be going to a lot of effort to make something that would approximate firebrick, with no guarantees that it wouldn't spall/crack etc. Some wise advice too about time being the biggest cost here.

              I think I'll go with the tried and tested firebricks - I can't imagine how annoyed I'd be if I made a bunch of geodesic tiles that fell apart after a few months use...