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Planning my 32" cast oven

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  • Ronstarch
    replied
    I generally agree with everything david s said (as is usually the case). I use perlite rather than vermiculite, just because that's what is available near me, and it has worked well. I also use a richer mix, more like 5:1, because I figure I'm already getting great insulation from the ceramic fiber blanket, and I find it easier to work with the 5:1 mix, even though it's less insulative. I was buying perlite in 2 cu ft bags at Home Depot for about $20/bag, then found it at local farm/garden supply stores in 4 cu ft bags for $25.

    Regarding tool length, for my 29" diameter oven, I use wooden peels with a 24" handle, a stainless steel turning peel with about a 40" handle, and a 48" long blow pipe for clearing ashes. The turning peel and blow pipe could both be shorter, but I have the space and the extra length doesn't hurt. I also have a pair of welding gloves in case I need to reach into the oven.

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  • JRPizza
    replied
    AndreasP, you need long handled tools or fireproof arms
    Seriously, I think the shortest tool I use is an old fireplace poker that's about 3' long. When the oven is going and I am working a live fire I can singe my arm hair if I get anywhere in the vent area. I guess my point is whether you have a long or short vent area you will want some long handled tools.

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  • AndreasP
    replied
    Thanks Ronstarch and david s , appreciate the feedback, I guess I will have to try and find Vermiculite. Will give it another try.

    What length tools do you use? My first decision is the location of the oven. I will build a little template and try to see how it feels, but any input on the tool handle length would be great.

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  • david s
    replied
    Not only does the vermicrete layer over the blanket enable the restoration of the perfect hemispherical form, it also provides a firm substrate upon which you can render against. Attempting to apply a cement render against the blanket is difficult as it’s quite springy and therefore likely to result in cracks and a much thicker rendered layer is also required to fill any low spots. A 10:1 vermicrete has a similar insulation value as blanket and is firm enough to render on to.
    Most folk wrap the blanket in chicken wire. I don’t because it takes ages and although it restores the form somewhat, also compresses the blanket which reduces it’s insulating capacity. Also adding a highly conductive material like steel in an insulating layer also reduces its effectiveness. An inch and a half or so of vermicrete is plenty to restore the desired form.
    Last edited by david s; 08-29-2021, 06:05 PM.

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  • Ronstarch
    replied
    I like using vermicrete/perlcrete outside the ceramic fiber blanket, mostly for the ability to refine the shape of the dome. In my experience, it's challenging enough to just get the ceramic fiber blanket to conform to a generally spherical shape, let alone get it just the way you want it. With the vermicrete, you can add a little more here, a little less there, and wind up with the shape you want. If you skip the chicken wire, you may still need to use some type of wire or rope to hold the blanket in place, until you put the vermicrete on. With your extra blanket, you could do 3" all the way around, and/or add one more inch of insulation to the top 1/3 of the dome where it heats up the fastest.

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  • AndreasP
    started a topic Planning my 32" cast oven

    Planning my 32" cast oven

    Finally getting started with my own build (or at least the detailed planning) of a cast pizza oven. I have been dreaming about this for years.
    Here is a summary of what I am planning to do and I would very much appreciate any feedback anybody has.
    I am thinking of a 32" / 800mm interior diameter, since I don’t have too much space (especially depth wise)

    Location:
    • I already have an outdoor kitchen and am planning to include the pizza oven into the outdoor kitchen. I have attached a photo of the location. As you can see the kitchen is U-shaped. Ideally the pizza oven would go into the slope. I am thinking of placing it at an angle into the corner to give me more distance to the BBQ. Alternatively I could place it straight on. Two sketches are attached. Any thoughts?
    • Question: How much space do I need in front of the oven opening to easily maneuver with all the tools? Or in other words, how long a handle do you normally use on the tools. I am a bit concerned that I don’t have enough space to the BBQ
    Design of the oven stand:
    • I will have to dig out a bit from the slope (it will be above the current hip high retaining wall), place a foundation and pour the slab there. This means that I can’t have any weep holes as I have seen recommended, since the slab will be directly on the soil. We live in LA, so it doesn’t rain too much, I figure that should be OK, especially if I use FoamGlass for insulation.
    Oven floor:
    • Since the slab is right on the dirt I am considering using
      • 2” of FoamGlass (does not absorb water, and should help with keeping the floor dry)
        • Maybe make the Foamglass larger than the CalSil board so that the insulating blanket does not sit on the concrete slab
      • Question: I have seen people using mosaic tiles on top of the slab to insulate the Vermicrete from the possibly damp slab and help water / moisture finding its way to the weep holes. I am not planning on using mosaic tiles, since don’t have weep holes or Vermicrete. Any thoughts?
      • 2” of Cal Sil Board
      • Fire bricks
      • Question: I have seen different types of firebrick, light duty, heavy duty. Any preference, what should I look for when selecting firebrick?
    • I am planning leaving a 1/8” gap between the oven floor and the floor of the gallery and fill it most of the way with 5:1 Vermicrete (probably sift out the larger pieces), the rest will be filled with ash.
    Oven Dome:
    • I will cast the dome with Homebrew 3:1:1:1
      • Sand: max 3mm grain size, considering using pool filter sand
      • Hydrated Lime: planning on using Type S hydrated lime
      • Portland Cement: whatever is available at Lowes, Home Depot, etc.
      • Clay: planning on using any powdered clay I can find. Thompson Building Materials has some
    • 2” thick
    • Cast dome on top of the fire bricks. It will make it easier to cut the bricks (don’t have to be as exact). I know I won’t be able to remove the bricks around the sides, but from what I have read that is not really an issue.
    • Planning on casting the flue gallery separately, making sure that there is some extra space around the chimney pipe
    • Attach the flue gallery with 5:1 Vermicrete (probably sift out the larger pieces)
    • Question: would it be better to use high temp mortar made for fireplaces? I think the whole point is to allow for expansion of the dome separately from the gallery. If I decide to just use ceramic blanket for insulation (see below) I may not have Vermiculite. I was having some trouble finding it.
    Oven Dome insulation:
    • I will insulate with two layers of 1” 8# ceramic fiber blanket (2” total).
    • Don’t use chicken wire to tie down the insulation, should not be necessary, Vermicrete will keep insulation in place
    • Add 2” of Vermicrete 10:1 mix
    • Question: Would it make sense to just use 4” of fiber blanket and not use any Vermicrete? If my calculations are right, I should be able to get almost 4” out of 50 sqft of blanket that come in one roll. Dome and Gallery surface total area is 14 sqft total (without subtracting the opening of the dome where the gallery connects). I am having a hard time finding vermiculite in LA (all the horse supply stores and several nurseries I called were sold out and don’t know when they will get it back)
    • Use a breather vent (hydraulics breather cap) screwed into a ” brass pipe with holes at the top of the dome. I have seen other methods of using the chimney area to vent, but it may be a bit too complicated for me.
    Final render layer:
    • I am planning on using stucco to finish the oven. I won’t be able to build a roof over it. It will be too massive where the oven is placed. I am planning to simply cover it with a tarp (or maybe a homemade cover cut to shape) during the winter (when there is at least a chance of rain) or when it is not in use
    • Question: Any suggestion for what stucco to use? I am currently planning on using an acrylic stucco with some AR Fiberglass fibers (12 x 0.5mm), I am planning on a to in thick layer. I am not planning on painting it
    Again, any help, suggestions, criticism is VERY much appreciated.
    I will most likely not start this build for a month or two, will wait for colder weather to make sure the dome does not cure too fast.
    Last edited by AndreasP; 08-29-2021, 03:11 PM.
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