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2 meter diameter New build oven with pumice reinforced with Basalt Rebar

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  • #46
    Originally posted by Gulf View Post
    I may have a different understanding of exacly what type of "bubble aluminium thermal insolent" that you are referring to. Aluminum melts @ around 700 degrees F. Im not sure that 1" of ceramic fiber is enough insulation to prevent that from happening at the apex of your dome. The type of insulation that I am famiiar with ( aluminum foil on both sides) has PVC plastic foam with air filled cells that will melt at an even much lower temperature. . The aluminum foil will also help keep moisture in, if there is no other means for it to escape. Some of us have installed vents for this.

    Three inches of ceramic fiber blanket or the equivelant is the minimum recommended for the dome. I think that it takes twice the thicknesss of 10 to 1 vermicrete to be the equivelant. So, that would be at least another 4" of vermicrete. I hope that others will comment on the pumice. I have no idea what that adds or subtracts from insulating efficiency.

    You really need to think again about covering this beast with roof to keep the water out imo.
    Thank you again for the great info.
    In this case, I will add 6 inches of vermiculite mixed with pumice as a thermal insulation.


    Will tiling the dome using a Dunlop specified for swimming pools ( Water proof) tile adhesive for swimming pools be a good option to protect the exposed dome from water going through dome cladding?

    Perhaps, adding a layer of water proof black paint (made of asphelt) on top of the 6inch cm vermiculite is safe enough?

    Unfortunately, I live in a green belt with a local committee of retired people, I have aggravated them during the 4 year waiting for the oven to be completed, as the oven is visible from the outside ....my next door has contacted the local council and the local fire brigade as well as the planning department to stop the construction of the oven. Therefore, canopy is out of the question as I may be breaking the deed of the land/house purchase> I need the shelter for keeping the oven dry as well as protect it from a falling falling tree as the garden is part of a woodland.I have incorporated some steel into the concrete hearth with the intention to add acro supports at each corner to provide a metal frame to protect it from medium size branches falling on windy days..
    Attached Files

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    • #47
      Alomran,

      It doesn't appear that you have enough room on the sides of your hearth for the insulation layer. I'm not sure about the back. I had the same problem. I took care of that by pouring a reinforced concrete cantilever ring to support it. After forming the ring, I placed a thin sheet of roofing metal against the ceramic fiber insulation. My thinking was that it would help keep from compressing the insulation and keep the insulation from wicking water from the concrete. Once that had set I installed the vermicrete. The last pic shows a mesh that I installed over the vermicrete with spacers. I then installed what I called at the time a stucco layer. It was not a coventional stucco application. More like water resistant ferrocrete. That layer is very strong and water resistant. It is not a breathable layer like true stucco. That is where a vent comes into play and is very necessary with a water proof outside shell. I did lot of cooking in the oven prior to installing the brick venier and had no cracks. To date there are no cracks in the outside shell.

      Since you will not have a roof cover, make sure that you build up the area behind the chimney level with the apex of the dome before installing your final render/stucco and or tile.
      Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build

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      • #48
        Originally posted by Gulf View Post
        Alomran,
        Since you will not have a roof cover, make sure that you build up the area behind the chimney level with the apex of the dome before installing your final render/stucco and or tile.
        Thanks Gulf for the great idea about cantilevering concrete. I was going for an over kill by bolting L shape metal to hold the vermiculite+pumice mix.

        Sorry, but I didn't get what you meant in the above quote ;(
        Did you leave the metal roofing sheet sandwiched between the ceramic blanket and the vermiculite insulation? or did you pull it out?
        Is the light weight insulate Kiln bricks health hazardous with food?
        Last edited by Alomran; 10-02-2019, 03:24 PM.

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        • #49
          I should have elaborated a little more about that. You can see an example of it my pics above. Since I have a roof over the build, I have a good example of how not to do it. Where the dome meets the chimney can create a sharp valley where water can collect during a hard rain. This valley is a bad place for different types building materials to intersect, stucco/render to brick for example. That will result in a cold joint that is difficult to waterproof. Even with the same material, the sharp change in direction is subject to crack. That means water intrusion. If freezing weather is figured into the equation that means further damage. Building this area up level across from the apex of the dome or at least contouring this transition will save some problems in the future.

          Building without a cover leads to another area that needs to be addressed. It may well be the easiest point for water to enter the oven. That is the oven entry. Forno Bravo and some other companies address this with a brow over the entry. That will help with a normal rain. With a wind driven rain, that is not enough, imo. I included a storm door with my build for that. It takes another reveal on the face brick or in the stucco for it to work.

          Also, Make sure that the ledge or landing is lower and slopes slightly away from the entry for water drainage.

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

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          • #50
            Originally posted by Gulf View Post
            Sorry for the late reply.
            In my opinion, soft insulated firebrick should be sealed from any compartment that food is cooked or passes thru during the cooking process.
            I have put 2 pieces of Kiln insulate refractory bricks on the arch which I can replace easily, Is the light weight Kiln insulate refractory bricks present a health hazardous with food?

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            • #51
              I have no idea about the food safe portion of your question. Soft insulated firebrick will shed small pieces when bumped with peels, pots, and or insulated doors. Those pieces getting on your food is probable.... Hazardous, I don't know? It is just not a best practice imo.
              Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build

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              • #52
                Originally posted by Gulf View Post
                I have no idea about the food safe portion of your question. Soft insulated firebrick will shed small pieces when bumped with peels, pots, and or insulated doors. Those pieces getting on your food is probable.... Hazardous, I don't know? It is just not a best practice imo.
                Gulf: I cannot thank you enough.. I honestly think if it was not for the advice I had from you and some others, my oven would have definitely been now a rubble....I am not saying it won't but less like since I am using firebricks and right approach. A great forum and a great entourage of oven builders. It has definitely been an experience. I have never realised how complicated building an oven properly.. Definitely far more complicated than any building I have designed.
                Thank you for taking the time to answer my queries.

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                • #53
                  Originally posted by Gulf View Post
                  Alomran,
                  . Once that had set I installed the vermicrete. The last pic shows a mesh that I installed over the vermicrete with spacers.
                  Gulf: how long did it take you to finish of vermi-crete the entire dome?

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                  • #54
                    I was going to say 2 days. But, looking back at my album, I can see 3 separate stages of drying. I'm sure that these weren't full days. Just, what time that my schedule would allow.
                    Last edited by Gulf; 11-23-2019, 05:42 PM.
                    Joe Watson " A year from now, you will wish that you had started today" My Build Album / My Build

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                    • #55
                      When you mix the correct amount of water with the vermiculite to make a vermicrete mix, because it is so water absorbent, you will be adding more than twice the amount of water that the hydration reaction requires. That means an enormous amount of free water left in the vermicrete layer. If the layer is thick it takes longer to eliminate the water. See my experiment on drying to give you an idea. You could fire the oven with just the blanket layers and it would function fine, the only reason to cover it with a more permanent outer shell is to prevent the blanket from getting wet with rain and to protect it from abrasion damage. The blanket is difficult to render against because it's somewhat springy and also a bit lumpy which then necessitates a very thick outer rendered shell. So, the usual method is to give the blanket a layer or two of lean (10:1) vermicrete which evens out the lumps and bumps and once set and dry is firm enough to render against while also providing an extra insulating layer. If it is made any thicker than an inch or so, then drying becomes difficult. When I first began making ovens the older generation of blanket was not classified as safe and the safe stuff now used was prohibitively expensive. Consequently I insulated entirely with 10:1 vermicrete and quickly found that it was best done in layers of around one and a half inches thick with a week of drying before proceeding to the next layer. I now use a blanket layer over which I do a vermicrete layer, then after a week of drying the drying fires and finally the rendered outer shell. Vermicrete insulating slab copy.doc.zip
                      Kindled with zeal and fired with passion.

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                      • #56
                        Originally posted by Gulf View Post
                        I was going to say 2 days. But, looking back at my album, I can see 3 separate stages of drying. I'm sure that these weren't full days. Just, what time that my schedule would allow.
                        I have a question: How long does it take take for a dome with home-brew mortar to dry up prior to firing the oven for curing it in a wet country like the UK?
                        What is the formula that works out the flue diameter from the dome's diameter? My dome's diameter is 197cm, with the height of (approx.) 78cm any idea how to work our the flue's diameter?

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