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  • Re: Steel Dome Oven

    There's no reason to go denser than the 5:1 ratio recommended in the instructions. It will have plenty of compressive strength after it cures, but the more portland you add, the less insulation properties the concrete will have.

    Builders have gone as high a 12:1 by power mixing the portland with water to create a slurry, and then mixing in the vermiculite or perlite.
    My geodesic oven project: part 1, part 2

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    • Re: Steel Dome Oven

      Fireplug (aka Kevin),

      Insulating concrete is only good in compression, I do not have any numbers but would not expect it to very strong in either shear or tension. As such the insulating layer needs to be supported. For a trailer a properly designed steel support need not be overly heavy. The weight of these ovens is primarily around where the dome itself sits. The weight in the center is actually quite low in comparison.

      I would think you should have no problem with a better insulating ratio than 3 to 1. Mine was closer to ten to one of vermiculite to cement and I would think one could easily get similar to that with perlcrete.

      When thinking of the weight of a WFO it is good to remember the great majority of the weight is distributed over the actual area of the base of the supporting bricks. While our WFOs are different than the usual WFOs made with bricks they still have a large footprint relative to their total weight. For example: A 4.5 inch brick on it's end of 2.25 inches has a square area of 10.125 inches. So say there were 30 soldiers in the base of an WFO and the dome of that WFO weighed 4000 lbs. That would work out to 30 x 10.125= 303.75 square inches to support 4000 lbs or 13.1687... lbs. per square inch. That's not very much. The total is a bit of weight, but per square inch of area beneath the insulating layer doesn't need much strength to support so little weight. And those figures are high as we left out the grout in the wedge shaped space between the bricks which is increasing the support area and depending upon the insulation of the dome (percrete or vermicrete) some of which is also self-supporting. Now what you are building as well as what I built is different in that we are/didn't use firebricks but the same principle applies just our material is different.

      So my suggestion would be to go with a reasonable support upon which you pour a high ratio (9 or 10 to 1) insulating layer. Also I would suggest you design the insulating layer so that it incorporates a split of firebrick upon which the steel sits. This is what I did with my WFO and my reasoning was this:
      The steel will expand and contract as it heats and cools. This will cause movement and I didn't want the steel working/worrying its way into the softer insulating layer. By having it set upon a the harder firebrick this movement should have little or no detrimental effect.

      Hope this helps,
      Wiley

      Comment


      • Re: Steel Dome Oven

        Hey Wiley,


        Trailer is built ,oven is built,I need a vacation.I also welded spikes all over the dome so it can be one with the cladding.should I put kaowool down between metal dome and cladding for expansion? how does this recipe look for my heat sink cladding?aka refractory concrete.

        3 part 3/4 inch basalt
        2 part sand
        2 part calcium aluminate cement fondu
        1/2 part lime

        this recipe comes from traditional oven.It seems correct.

        I can purchase 94 lb bag of fondu for $45 10 min from my house I thought this was a pretty good deal.
        and 1/2 ton of basalt for $20 also near my house.

        Thanks for all your help and input...kevin

        Comment


        • Re: Steel Dome Oven

          Hi Kevin,
          Finally I have a working and hopefully safe, virus free computer system. I just got back online using this machine this evening and of course the first place to check...Forno Bravo!

          Regarding your question: If I am understanding correctly, you are asking whether you should place some kaowool between the steel and the basalt fondu concrete mix. I would say no. I would suggest you simply place a layer of aluminum foil between the two. The kaowool goes on after the cladding.

          The aluminum foil wil create a slip surface so the steel can expand and contract and whatever movement should be accommodated. I suggest that when you apply the concrete that you create some larger polygonals so that the pieces of heat sink can act as individual plates. We've discussed this before, the idea is sort of like a snake skin. The actual scales in a snake skin are rigid. The expansion needed as the snake respirates is accommodated between the individual scales. The plates are held to the steel liner by the steel spikes.

          Great to learn that your project is coming along...some pictures would be nice:-) That seems like a good price for Fondu, compared to traditional portland cements it is fairly expensive but IMHO, worth the cost.

          Hope this helps,
          Wiley

          Comment


          • Re: Steel Dome Oven

            Kevin, I'm not as sharp as I once was (was I ever?), however, something about your mix sent me searching for something I remember reading. Back in 2008 there was a thread about casting and a proper mix; David S. in Australia had this addition:


            Originally posted by david s View Post
            Lime and calcium aluminate together are not good. I've tried this and the lime acts as an accelerant to make your brew go off much faster. The calcium aluminate is also quite temperature dependant. On a cold day it takes ages to go off (use warm water) On a hot day it'll go off really fast (use chilled water or some ice) don't mix product that's been sitting in the sun. It's also quite thixotropic ie It'll start going hard but if you give it more mixing or vibration it liquifies again weird stuff.
            So you might want to keep that info in mind when you start mixing your brew. Calcium aluminate goes off pretty fast on it's own. Also I would see if your source for basalt has it in something smaller than 3/4 inch. My thinking is you would want something more like "xx minus". The minus in crushed rock terminology means it will have finer/smaller particles of the same material intermixed in the load. Having the fines of the same material would make for a final mix with more consistant characteristics throughout, as opposed to adding sand of unknown composition. My personal choice was 1/4 minus as a simple one step mix. I didn't have to add or measure out anything but the Fondu to the stuff. It's your WFO and so you will do as you see fit (as to be expected and hoped).
            Bests,
            Wiley

            Comment


            • Re: Steel Dome Oven

              Wiley

              Makes sense,1/4 basically has the caricature of sand,and now that i think about it i think the basalt supplier said 1/4 inch minus that will save me a step thanks,I followed up on the lime, I guess you only want to use lime with normal cement the lime help's keeping the cement from burning out.so if I use fondu I won't need it....thanks again.

              Kevin

              Comment


              • Re: Steel Dome Oven

                Wiley,

                I went back and looked at you pic's,and wanted to know if you formed up your cladding triangles? or did you form the triangles against the steel dome as you went. how long does it take to set up? I'm going to start on Friday and hope to be done on Sunday,Thursday (tomorrow) I'm going to build a fire and hope it vent's well. I used a 6 inch chimney from home depot.we will see thanks again...kevin

                Comment


                • Re: Steel Dome Oven

                  Kevin, I formed up as I went. I would bring to your attention the initial form which I made around the base of my WFO. This allowed me to get past the "vertical" (where the concrete is standing and supported upon itself ) and to be forming against the dome (cylinder). The further up the dome/cylinder the more the concrete is supported as opposed to the concrete standing on itself. Casting the ring around the base also allowed me to get a feel for how easily the material works and how soon it kicks off.

                  When forming the triangles I created them by eye and placed aluminium foil between the joins. I pressed the foil into the just formed triangles before it fully set off. This mandated the expansion joint occur where I wanted it to occur rather than form (crack) at some perhaps less desireable location. The size of the triangles was determined by the size batches I made...again learned by casting the initial supporting base mentioned above.

                  The stuff goes off quickly and one is advised to have a plan and have tools laid out etc. Not to panic you, but figure 20 minutes from mixing to unworkable, so not a problem with a reasonable size batch but no time to go looking for that trowel or aluminium foil. By the end I found I enjoyed working with the material, it easily and quickly assumed an initial set and allowed one to hold shapes with a trowel in one hand and shape with a trowel in the other; after a few moments the held material would stay in place (allowing it to be smoothed and faired into the rest) where with regular cement/concrete it would have slumped when released.

                  I also found that I had good results by mixing a batch and then cleaning up the wheel barrow (where I mixed it) with a hose and brush. Then starting a new batch. By the time it was mixed and ready to go the previous batch was quite hard and I could form against it without damage. You should have no difficulty alternately working one side and then the other of your cylinder.

                  Hope this helps, looking forward to some photos...
                  Bests,
                  Wiley

                  Comment


                  • Re: Steel Dome Oven

                    Wiley.

                    You used 5 to 1 ratio for your cladding?

                    thanks...kevin

                    Comment


                    • Re: Steel Dome Oven

                      Yes, by volume 1 part calcium aluminate cement to five parts 1/4 minus crushed basalt. Check post number 48 in this thread.
                      Bests,
                      Wiley

                      Comment


                      • Re: Steel Dome Oven

                        Wiley,

                        I have been reading your thread from the beginning - what an excellent project and well documented from the beginning.

                        Lots of great ideas.

                        Thanks
                        Provin

                        Comment


                        • Re: Steel Dome Oven

                          Wiley

                          It's been a while, my project is done and you can see some pic's if you google kindle kart, It should bring up my facebook account and you can go through my photo's of my wood fire pizza cart in Portland.I think the oven is very well built I love the steel dome for transmitting heat on my oven floor,but I would do a couple things different,the main issue is my dome is 28 inches away from the floor although my floor gets hot enough I think it should be more like 20 inches.
                          The oven is big 5ftx5ft inside measurement,also I think my oven opening is to big letting too much heat to escape out the door and up the chimney. Do you think 20 inches sounds correct for floor to top of dome ratio?I plan on taking all my fire bricks out pouring a 6-8 inches more of insulation concrete then putting firebricks back.I really don't care how firebricks cook my pizza so I might add a slab of soapstone on top of my firebricks,Any thoughts on this?Do you know a good place to buy soapstone in the northwest?


                          Thanks for all your help....kevin

                          Comment


                          • Re: Steel Dome Oven

                            Hi Kevin,
                            First, you're more than welcome for any help I was in the design of your WFO. This forum is great for alternative ideas and mutual sharing of thoughts on our unusual creations.

                            I'm not on Facebook so I couldn't view the photos of your finished WFO. Regarding the height of internal dome and height of door: It is my understanding that that ratio (63%) is an emperical one derived from study of lots of successful WFOs. It has do do with airflow and proponets state WFOs with that ratio allow for incoming air to most efficiently supply air to the fire and exhaust the products of combustion (gasses smoke etc). I usually try not to reinvent the wheel and so go with what works adding my own twist on what I'm doing. One does need to keep in mind that with such departures from the norm there is a risk of less than hoped for results.

                            As I haven't seen your photos I do not know how difficult it would be to fabricate a temporary structure to lower the door height to see how that effects the performance of your WFO. As for too great an interior height that could be reduced by raising the floor (which would also lessen the door height and change the ratio). Of course that would change the working surface height as well as the heat up times (due to greater mass) as well as the weight of the finished WFO. Lots of factors to consider. But it wouldn't be much work to lay a temporary layer of bricks on top of the existing floor and so test the idea of lessened door and ceiling height. Five foot by five foot is a large WFO, you must have a source of inexpensive firewood.

                            My next WFO will be a steel dome as well (yes, I plan on building another, perhaps next year at a campsite/trailer site I'm constructing next to a pond I'm digging right now at the other end of my little five acres). I hope to find a condemmed propane cylinder which has elliptical ends. This will make for a WFO with a lower ceiling. Not that I'm dissatisfied with my hemispherical WFO just the new WFO will be strickly for pizza and other low dishes. However, at the speed of my construction and demands upon my time it may be built the summer after that, but it is in the plans. I've attached two photos of bucking up some of the logs from the trees I've pulled over at the pond site (one gets the root ball out at the same time as one drops the tree if one pulls a tree over), and one of the same logs split.

                            I don't know of any source for soapstone here in the PNW.

                            Bests,
                            Wiley

                            Comment


                            • Re: Steel Dome Oven

                              In Portland go to Precision Counter Tops for Soapstone. You will get your best pricing on remnants and left over cut outs. Even at remnant prices a 60" oven would be expensive though. Go talk to My Fiance Molly at Precision she'll be happy to help you.

                              Comment


                              • Re: Steel Dome Oven

                                Wiley, I too plan on a campsite oven (moveable if necessary) and another at my home....
                                AND I'm a midwest sailor!...I've really loved and been tremendously informed by this site and especially by your thread...can't thank you enough...
                                anything to add in retrospect?
                                Thanks again, Bill

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