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pete zapie 02-29-2012 06:30 AM

24" cast mobile oven
hello all, getting close to casting my 24 inch oven . thanks for all the info on this site , what an amazing resource you all have created !
this oven will be three sections:

1. dome - 24" inside dia. , 2" thick wal
2. flue chamber - should this be refractory cement ?
3. cast floor/ cooking surface or is fire brick preferred

my plan from bottom up:

metal pan / tray
hearth/insulation board .............. how thick and which type ??
cooking surface .............. was thinking of cast unless brick is better
dome .................. one peice 24" dia, 15" ht, 2" thk walls
flue assbly. .................... thermal break , refractory castable?
insulation ..................... at least 2" ceramic blanket
exterior render ..................... the usual stucco stuff

my questions/concerns:

1. what type of insulation board and how thick , some say 2" is fine others say 3 or 4 is nesscary.

2. i thought i would cast the floor as long as im casting the other parts - it would probably be 2" thick or is a brick floor prefered.

3. the dome will be formed in a mold over a 24" rubber ball held to 15" high . i will later decide to build the oven around the floor or on top of the floor for extra cooking height. I originally wanted to go the home brew route but not sure about the exact mix with all the fibers and all , just not confident about the recipie so i was leaning toward purchasing the castable cement.
also are stainless needles still recomcnded?

4. flue , this will be a seperate peice with a thermal break: will ceramic rope work to fill the gap of the thermal break? does this peice have to be castable refractory, i have read that it might be better to make it out of a lighter material?

5. insulation: at least 2" ceramic blanket ..... more?? i was thinking 3" any opinions ??

6. finish render: havent given it much thought yet

so thats basically it so far , any suggestions will be greatly apperciated ---

brand thickness type of f/b/ board
opinions on cooking surface brick / cast
brand thickness type alumina % of castable
how much ss needels if nesscary
flue chamber material and thermal seal seal { ceramic rope?}
type and thickness of insulation

thank you for looking at my build . i look foreward to your feedback and advice,dont hold back lets get to the point and get this thing built.

pics of my dome and chamber mold to follow asap {first time uploading pics}
thanks again for looking!!

pete zapie 03-04-2012 07:16 PM

Re: 24" cast mobile oven

david s 03-05-2012 04:10 AM

Re: 24" cast mobile oven
1. 2" calcium silicate board is plenty, IMO, but you can have more if you want.

2. You can cast the floor if you wish, but large casts of castable refractory are prone to cracking, particularly in the floor where the heat is rapid and uneven, resulting in uneven expansion rates. A 24" diam is small, but you will get a crack right down the middle. This is not really a problem because if you cast it in pieces or use firebricks you are designing the cracks anyway.

3. not sure exactly how you plan to cast over a rubber ball. Presumably you will dig a hole in the ground to hold the bottom hemisphere with a circular baseplate around the middle of the ball so you get a good flat and level base on the dome. This sounds like a lot of trouble. I think a sand castle is an easier option the you can cast over it in place, eliminating the need to move the dome. Stainless steel needles are the recommended reinforcing, but you can do it without them, the dome will stand on its own as it is a self supporting structure.

4. The flue gallery does not have to be castable, but as it is better to have it funnelling towards the flue pipe, castable lends itself well to compound curves. Stainless steel sheet would be a suitable alternative.

5. 2" ceramic blanket is plenty IMO, but it depends how you want to use your oven. I prefer to use vermiculite as it is a safer material, but you need to make the insulation layer twice as thick to achieve the same insulation value.

david s 03-05-2012 04:17 AM

Re: 24" cast mobile oven
I think a metal pan or tray is not a good idea as it will tend to trap moisture between it and the oven resulting in accelerated corrosion (unless you use Stainless) Anything in steel is going to rust and should be avoided IMO. I think a concrete base is preferable

pete zapie 03-05-2012 03:56 PM

Re: 24" cast mobile oven
david thanks for the reply. i tried to upload a picture of the form but it didnt work , ill keep trying. as far as the base ,do you think cement board/ hardibacker on 3/4 ply on a frame is acceptable it being on wheels and all I was concerned about cracking. as for the insulation 2 is enough for pizza but maybe more is needed hold the temp for a day or so?

david s 03-05-2012 04:57 PM

Re: 24" cast mobile oven
Make sure the base plate of your form is strong enough that it won't distort too much with the load of the casting and also make sure it will release from the casting. You could use plastic sheeting, I use 50/50 kerosene and motor oil.

Because your oven is small it will use very little fuel, it is no problem to kick in a bit more heat. How often do you think you'll be wanting to cook the next day anyway? Because the oven is small the door will be a greater % of the inner dome surface and therefore will have a greater heat loss than a big oven even with an insulated door. My 21" oven only uses 4kg of wood to reach 350C (when it is dry)

pete zapie 03-06-2012 05:53 AM

Re: 24" cast mobile oven
i went to purchase the castable material today and hooked up with somebody who had a unused 32" ss needle reinforced factory made oven and cast floor that sat in his garage for a couple years that he had to unload asap. he was asking about 100 bucks more than I planed to spend on the castable refractory so i went for it. I still want to cast with the form at sometime, so I am still going to post pictures of it because I'm interested in what your opinion might be,thanks again for your interest. I now have advanced a few steps in the oven building process and will be setting it up on the trailer now.
you mentioned that a metal pan was not a good idea to place the oven on so i was thinking about .... oven on top of cement board, on 3/4 ply wood , on a frame base.

the oven is bigger and heavier [450 lbs]than planed so the trailer being on the smaller side probobly wont be used for road trips but just wheeled locally by hand till i can upgrade it. so this is my idea ....... I will set it on the trailer platform , 2" super isol , cast floor , cast oven , 2" ceramic blanket. i will cover the oven with a house that will fit around and attach to the base. then when I find a larger trailer I'll be able to unscrew it and move it to the larger trailer being able to reuse everything ..... or is this line of thought not right.

pete zapie 03-06-2012 08:23 AM

Re: 24" cast mobile oven
I mean is an oven moveable - taken apart and reassembled- once its been fired

david s 03-06-2012 12:29 PM

Re: 24" cast mobile oven
You don't mention how heavy it is, but is sounds like you will definitely need a double axle trailer.

pete zapie 03-06-2012 02:37 PM

Re: 24" cast mobile oven
its 450 lbs and what do you think about resting it on the plywood

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