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Casting Refractory - This is NOT a drill! - Forno Bravo Forum: The Wood-Fired Oven Community


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Casting Refractory - This is NOT a drill!

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  • Casting Refractory - This is NOT a drill!

    Well I've done it. Over the last 4 days I've cast an oven entirely out of refractory castable (Mizzou Castable Plus). I'll break this up into a few posts with attached pix.

    First I used Solid works to model a Volto Basso with a 42" diameter and 17" height. I used the sketch from that to make 1/2" plywood ribs for the forms you see in the pics below. The cutaway is what allows you to remove the forms from the oven later, barely.

    More in next post,


  • #2
    Re: Casting Refractory - This is NOT a drill!

    Next I fiberglassed the forms with 4 oz S Glass and Epoxy. These are just what I have laying around. E-glass and polyester, or heck even a coat of urethane will probably do.

    I couldn't help but throw in a shot of the view from the PPP (Pizza Picnic Pavilion) site. Site, as the only thing there right now is the oven, the rest will come.

    The stand is fairly standard, so no details on that.

    The hearth pour is different in that the pearlcrete is limited to the actually footprint of the oven. I poured the platform and left an area in the center where the solid concrete with rebar is 3" thick. This will be fine as the bulk of the ovens weight bears on the perimeter. On this I poured (and I use the term loosely) 4" of pearlcrete. I did use the cement mixer for this and it worked fine with no apparent degradation of the pearlite.

    On that I poured 2" of the Mizzou Castable Plus. I chose Mizzou in consultation with Dave at ANH refractories because it has a density, specific heat and thermal conductivity that is very close to fire brick. You can see the cooking surface pour in its form, which is really to get the straight edge at the front to tile up to later.

    More in next post,



    • #3
      Re: Casting Refractory - This is NOT a drill!

      Then, I set up the mold segments on the cooking surface and screwed them to and endplate that defines the midline of the dome. I added and additional form for the arch and on top of that went an 8" concrete footing tube.

      Here is where the wheels came off! I was under the impression that this material was intended to be troweled onto a vertical surface. WRONG! Conrete just like poop flows downhill. Needless to say we scrambled like mad to set up some outside forms. This also necessitated multiple pours, which may cause problems down the road. All the pours were in rapid succession so bonding should be good, but you never know. If I cast another oven, I will make matching female tooling for the outside. As it is, the wall of the oven varies from 2-1/2" - 4-1/2". What can I say, it is what it is, highly experimental.

      The last pic shows the nesting form tubes for the chimney. The outside just peeled off in a spiral, the inside will either burn out during the curing phase, or will be cut out later.

      At this point old timers will be gasping "where is the reinforcement in the arch ?". But,not to worry, Mizzou is a short fiber reinforced concrete. It's a bit like the new fiber reinforced stucco. Any reinforcement would actually be detrimental, as the refractory expands twice as much as steel! So, either the steel stretches, or the oven breaks. At any rate this shell feels bombproof!

      Oh yeah, elves came and layed some nice granite tile last night. Must be in cahoots with my wife.

      More in next post,



      • #4
        Re: Casting Refractory - This is NOT a drill!

        Now we just need to get the forms out of the oven. This was enough of a challenge when I had open access with only half of the oven cast.

        Let me back up a bit. I reused the 4 segment molds to cast the second half of the dome, and yes they're in there good.

        I reached in with my trusty cordless drill and made a pilot hole for a big lag bolt through two ribs in the first form. I bolted a honkin' chain to it and with a mighty yank, out it came. And so on for all but the last form, which was up against the first half of the dome and was destroyed in the process of removal. Bummer, BUT the shell is cast and suffered no damage during demolding.

        The shell now sat there at 100F from baking in the sun. I build a small fire and ramped up from that to 350F over about 3 hours, holding my breath all the while. Phew, no loud CRACK ensued, and all is apparently well. Tomorrow, I'll camp out down at the PPP, and see how far I can go without insulation on the outside. For the detail oriented the dome hit 350F, while the floor only hit 210F and the outside of the top hit 150F.

        I'm planning to pearlcrete the outside tomorrow and to fire again Thursday ramping up and Friday all day hard to drive out moisture in the pearlcrete. Aggressive, yes, but if the shell is still crack free I don't care if the few show in the insulation. If all goes well, Friday night is first pizza. Otherwise, Saturday.

        More next week. Triumph or disaster? Stay tuned.

        At any rate I am STOKED,

        Enz, out.


        • #5
          Re: Casting Refractory - This is NOT a drill!

          Details, details. The ones I've left out that is.

          I should have mentioned sheeting the forms. I used an 1/8" Italian poplar bendable plywood from Southern Lumber. At $35 a sheet, it's probably the cheapest thing at Southern. You can see the sheeting in the last pic in the first post.

          Mold release: I used an old tin of Meguires past wax. I figure it will burn off before the first pizza, besides it's only on the dome and no the cooking surface.

          I'm sure that there will be many more questions.



          • #6
            Re: Casting Refractory - This is NOT a drill!


            Where to start? The location is wonderful. The form work looks very precise.

            How long from pour to fire? Are you worried that it has had long enough to cure before firing? I don't know much about castable refractory - but when I used to work on boilers - any shut down time was unacceptable - so we would press castable insulation into service very quickly and never had any failures there. But the two materials could be very different animals.

            I worriy that the vermilulite/cement mix will not cure fully if only given a day before the first big fire.

            How much do you think you have invested in materials at this point?

            I loved the part about having to yank the form out with a chain. I cannot believe the amount of excitement we have here on a daily basis.

            Again - Beautiful Job, beautiful location, and nice elves....

            My oven progress -


            • #7
              Re: Casting Refractory - This is NOT a drill!

              Thanks Christo!

              In a word Yes, I was worried about the quick cure, even though Harbison Walker specs a 24 hour cure and 100F/hour ramp after that for up to a 9" pour. But all is well! I fired up to 300F Monday night, 650F last night and up to operating temp today. The floor reads right at 900.F and the dome is at about 835F. So, I made nachos for lunch. Mmmmmmmm. 45 seconds, any more and they immolate. A huge load off of my mind at any rate. First pour was Thursday night and the second Saturday, so six days from forms to pizza temp.

              I have come to the same conclusion on the pearlcrete and will wait until after this weekends pizza to insulate the top. I'm having no trouble getting to pizza temps firing with red oak anyhow.

              Cost at this point is about $1650. The castable was $980. The granite was $100. The rest is concrete, rebar, blocks pearlite and forms. The forms were made from one sheet of 1/2 ply, a sheet of 1/8" Italian poplar bendable ply and epoxy and fiberglass I had on hand. Under 2 kilobucks, when its all said and done. Of course now I need to pour a 20 x 20 patio and build a pavilion with the rest of the outdoor kitchen. The oven is the cheap part.

              Time to make dough for Friday.

              Happy Fourth Everybody!



              • #8
                Re: Casting Refractory - This is NOT a drill!

                looks good!


                • #9
                  Re: Casting Refractory - This is NOT a drill!

                  Yo.. What is the latest on your oven? It's awesome.. Any more pictures?


                  • #10
                    Re: Casting Refractory - This is NOT a drill!

                    Thanks for the encouragement. Like so many others, after the shell is done and pizzas are flowing, I need to take a break. My house and family need some attention.

                    I'll be laying on 6" of perlcrete in a few weeks and after that it's stucco time. The next pictures should be of a completed oven.



                    • #11
                      Re: Casting Refractory - This is NOT a drill!

                      This looks amazing! I can't belive I found your post right away, you've done exactly what I'm hoping to do by casting your own oven. I've been looking into the many kits offered out there and can't belive the prices they charge for some very basic components. It all looks like precast refractory cement to me so I figure I could do it myslef instead. I'm still formulating my plan but I may have some questions for you down the line, if you don't mind?

                      Great looking oven!



                      • #12
                        Re: Casting Refractory - This is NOT a drill!

                        Sorry for the delay. I had the same train of thought. I'm guessing I save about $2300 over the kit. Feel free to contact me directly if you have questions.

                        I've now done pizza 5 times in a total of 8 burns. It's definitely fully cured. I roasted a chicken Saturday night after lunchtime pizza. What a treat. Incredible flavor. Almost better than the pizza. Did I say that out loud.

                        Now I need to stop making pizza long enough to insulate the oven.



                        • #13
                          Re: Casting Refractory - This is NOT a drill!

                          Thanks for the reply enz. I do have a few questions. I'll post them here in case others have similar questions, but if you'd rather not answer them on the forum I understand and you can email me directly.

                          My plan is to cast only the top dome and make a circular ring as a dome base out of standard fire brick, similar to the design for Superior Clays cast ovens:

                          This should reduce cost by eliminating some of the refrac cement Id need to buy. Basically the firebrick sides would take the place of your cast vertical sides.

                          Do you think the cement mix you used would be able to stick to a mold of about the shape in the pic without the need for an exterior mold to hold it in place?

                          Where did you get your refrac cement (Im in Redwood City)? Why did you choose Mizzou?

                          Any idea how many bags of Mizzou you used for just the body of the oven?

                          Do you know of good places in the Bay Area to look for fire brick and ceramic flew liners?

                          Lots of questions I know, thanks for the help.



                          • #14
                            Re: Casting Refractory - This is NOT a drill!

                            ANH Refractories is in Richmond, probably 45 minutes each way for you across the San Mateo Bridge.

                            They have Dozens of types of refractory concretes all listed on their website ( ANH Refractories ), but most of them are insulative. Be careful. I talked with their head sales guy (Bill?) to match the thermal characteristics of fire brick (density, emissivity and specific heat). The bonus with the mizzou was the quick heat up schedule.

                            They also have fire brick, insulation board, etc. It's one stop shopping. I don't know about flu liners, I ended up casting the whole chimney because I couldn't find the size I wanted. I didn't ask at ANH though, they might have them.

                            I used 25 bags total and had just enough with my varying thicknesses. If you make a mold for just the top and keep your thicknesses even, I think 10 bags should do it.

                            Good luck,


                            • #15
                              Re: Casting Refractory - This is NOT a drill!

                              how is the oven holding up?
                              spalling,cracks etc..?
                              Im thinking to cast one aswell this year!

                              cheers hendrik