Need help!! Building first oven!!!

[carrara]

Hello Everyone!!

I am starting my new build of a pizza oven and smoker combination, I have a bunch of questions first before I get too far. I love antique construction equipment and have collected it for 25 years, bulldozers, steam shovels stuff like that.... I have an older sheep's foot roller that was used to pack dirt when pulled usually by a bulldozer. This one is kinda mangled so I would like to cut out the center and line in bricks and make a pizza oven that looks like the cross between a porcupine and a stegosaurus. My questions are insulating thickness for the top marked C, this should be the hottest temp. Do you think i will have issues due to the bricks are expanding inside a metal tube? The wall thickness of the tube is 1/2" thick steel and 40 inches in ID. The fire for pizza oven part will go in A, the smoker fire box is B, and there is a metal plate i will put at D to support the bricks above. E is a port that goes from the back wall of B and up to the front of the A area to bring in smoke, and to add air to the wood fired pizza fire. The smoke will go out the pipe in the back and will eventually look like a dinosaur head. I have tons of metalwork experience but other than building a patio block pavers at our house i have zero brick laying skills and zero wood fired pizza oven skills. Please help!!!

Thanks
Dana

[david s]

Hi Dana,

This is an interesting idea and I'm all for using old stuff that has been designed for other applications. I'd be interested in seeing the outcome, although I'd expect it to be spectacularly unsuccessful because with such a large mass and volume of steel it will take a very long time to bring to a high temperature. Steel being way more conductive than firebrick would mean that it will suck the heat from the firebrick leaving you with bricks that are not hot enough. In addition the spikes will dissipate heat to the surrounding air because of their large surface area just like the fins on an air cooled engine. You would need an enormous amount of insulation over the whole thing to keep the heat in.

[carrara]

Hello David thank you for your reply!

I agree about the heat mass but isn't that the job of the insulation and high temperature brick to insulate the heat so it doesn't reach the outer surface? The better the insulation the less heat loss? I am hoping somebody can help me with some type of insulation to use. The insulation needs to be the best in the location of the highest temperature wouldn't that be the top section?

Thank you

Dana

[david s]

Yes it would have to be very well insulated. As steel is so conductive the heat will spread rapidly. You will have to insulate around and between all the spikes and then probably another 3" over the top of them. That's why I said you'd need an enormous amount of insulation. Ceramic fibre insulating blanket would be the best for this application.

[Damer419]

The spikes are way to awesome to hid beneath insulation...........that thing should be turned into a grill!!!

[carrara]

David,

Thanks for your input, i didn't realize how poor of insulating the medium duty fire bricks were. I assumed the amount of heat energy the bricks absorbed was enough to cook and also to insulate the heat to stay inside the oven. I didn't realize that its really the opposite, its designed to transfer the heat all around. Yes way too much thermal mass. But what if i cast or use insulating fire bricks around the outer surface or even just the top section, thats much hotter? This way the oven heats up like it should and there is a thermal brake. To keep the oven dimensions large enough there is a limit to the amount of insulation i can fit inside. And there is a limit to how much i can spend..... insulating fire brick is $$$$. In my new drawing i have the insulating fire bricks in green and the medium duty fire bricks in orange. Can you please comment on this?

Damer419---thanks..... i like the spikes too!!

thanks
Dana

[SableSprings]

Welcome Dana! I think this second approach is a better direction for the oven design than the original...as David pointed out, without separating the metal from the firebricks you'd have one smoking hot "Fornosaur" before you could do pizza. How about using the ceramic blanket material for the vault dome insulation (between the firebrick and the metal) instead of insulating bricks? Also, the cooking floor is not only going to need insulation but a base upon which to lay. You'll need to have a bunch of firebricks laying side by side on something... You might also consider the alternative of using some insulation blocks on the inside bottom, then on top of them add a piece of 0.5" thick cement board. Cut a piece of ceramic (CaSil) board and lay it on top of the cement board. Lay your cooking floor on that and build the arches so that you leave about 3"-4" gap between the brick and the curved metal. After the arches are in place you can slide/push the ceramic blanket into the gap. That would leave you a contained insulated brick oven with an incredible look on the outside.

I figure if you plan on leaving 4" (insulation/space) + 4.5" brick thickness (half brick) you'll end up with about 23" of cooking floor from your 40" available ID. Casting pieces instead of cutting firebricks could also gain you some space, especially if you cast a 2"-3" thick vault wall. I think David's oven is about 21" in diameter and he makes an amazing assortment (and quantity) of tasty treats. This seems like a doable and entirely awesome project...really looking forward to your progress.

[david s]

Yes, that's a much better arrangement. All of Mikes suggestions are also good. Casting a 2" thick half barrel vault in dense castable would give you the most useable internal oven space. Stuffing blanket over it between the vault and the the steel would also be way easier than trying to fit insulating bricks in that tight space.
it's not mandatory, but you probably want to have some kind of flue arrangement, perhaps something fabricated in thin steel?

[carrara]

Hello Mike and David!!

Thank you for your responses I greatly appreciate it. Due to your responses I went and did some calculations and studied the various thermal conductivity of all bricks and cartable refractory. As you can see i didn't do my homework before i started. Do you guys have any input for the brand or information for cartable refractory and bricks? I have used cast-able refractory before for some heat treating ovens but was under the impression that the outgassing was hazardous an it couldn't be used in the cooking chamber??? If i use cartable refractory i assume it needs to be lined with brick?

To answer some of your questions

I plan to support the oven floor with a plate of steel under the bricks. The lowest chamber in the center is a smoker box, i will line the top with bricks to protect the steel plate with a nice little arch. I will use casted refractory or a bricked chamber for the smoke from this to exit the back of the smoker box and move to the front in the side 1/4 circle areas (both sides) and enter the cooking chamber thru the floor in the front. I am not sure if i can also use this channel to supply combustion air when i am cooking pizza? I still have to figure out the door arrangement and what toe of insulation it will have if any?

Thank you very much for your help and input!

I made a quick drawing of the smoker smoke ports that i plan to use. I made a section view of one side. You can see the open port on the far side on the inside of the oven floor.

Dana

[UtahBeehiver]

I believe David is suggesting that a 2" dense cast with ceramic fiber blanket between outside diameter of casting and inside diameter of steel sheep's foot can be done in lieu of fire brick. You do not need to line with firebrick if you use dense casting material. This will be an interesting project to follow. You will need to insulate under the oven floor as well. Smallest footprint impact for the floor insulation will be ceramic fiber board, such as Thermogold 12, Inbloc, etc. should be at least 2" thick. As far as off gassing, I will defer to David, he is our resident casting expert.

[david s]

Castable refractory does not need to be lined with brick. It is used in place of firebrick. Make sure you use dense castable not insulating castable.

[SableSprings]

If you insulate the bottom area and then create either a cast or brick fire chamber below your oven floor and you'll have an option for a white oven. If your steel plate supports the cooking floor masonry of the oven chamber and doesn't use insulation, a controlled fire below will be able to bring the upper oven certainly into bread/roasting meat temps. To get pizza temps, you'd probably still need to build a fire in the upper chamber and keep it going during the pizza party. The ability to build the fire below gives you some interesting options for keeping baking temps fairly consistent over long periods of time without ash & coals and for smoking proteins...wow, sky's the limit.

You basically if you wanted both the white & black oven option, there will be a inner tube of insulation between the sheep's foot steel and the cast refractory and/or firebrick fire/smoke box & WFO upper chamber. In the French white ovens, the two "smoke holes" are covered with shallow pans of water just before the bread dough is placed in the upper chamber. Keeps any smoke tastes & smells from tainting the bread while it's baking. It does mean if you have a fire in the lower chamber and close it off from the upper chamber, there would have to be an additional exit chimney for the lower fire box. White ovens are more complicated than our normal black ovens, but you've got some really interesting options to explore.

p.s. Since David has cast and used cast ovens for lots of tasty food (and advised lots of people on this forum in their successful cast oven projects), I don't think outgassing from castable refractories is an issue. I'm also thinking there will be several people looking around for old sheep's foot rollers

[carrara]

Mike, David, and Russell

Thank you so much for your knowledge and pointers for this project, i greatly appreciate it. I worked on it yesterday and cut the outer frame off and noticed it was full of liquid. It has a bung on the outer side and i rolled it slightly and poured some of the fluid out in a pan and its 1/2 full of kerosene!!!! Can you imagine what would have happened when i used my oxygen- acetylene torch on this!!!! I pumped all the fluid and will let it drip/drain a while before i fill it with water prior to cutting out the ends. I will take some pictures and show you all the progression.

What do you guys think I should do with the door? Steel or steel door with a cast heat shield? Last summer I made a miniature stove for my daughter who likes to camp out in the woods and wanted to camp when it was literally 0 degrees F outside. I made a steel door with a steel shield to reduce the flame front from warping the door, which would have compromised the seal i used. I don't see as much heat in the area of door with this pizza oven/smoker as the little cook stove. I don't know if you guys have any ideas or opinion on this?

thanks!

Dana

[UtahBeehiver]

Lucky you discovered that there was kerosene in the chamber before you torched in. Filling with water is the safe why to go. I managed a weld shop for years. On the door, if you make "insulated" steel door you will be able to used the residual heat longer for cooking secondary products. As mentioned earlier by David S, carbon steel, SS, aluminum have really high thermal transmission factors (K) so an uninsulated steel door will be a heat sink. But if you are not concerned about multi day cooking then a uninsulated door may be the ticket.

[carrara]

David,

Your white and black oven idea is great!!! I had to do some research to better understand what you were saying. My wife is a wonderful cook and baker, where i am not, but with this hopefully that will change. I also want to keep the smoking ports working so i think i can make it all work by adding doors in the back of the oven that will give access to the rear flu where i can insert insulation bricks that will allow me to direct the smoke directly up the stack or thru the ports that go thru the cooking chamber. So hopefully this will be a white, black and gray oven, gray being the smoke section.

Dana