Casting a Slab

[Pizza2Night]

Hello, WFO lovers.


I am a really busy older woman but I do not eat “prefab” food. Generally I make everything from scratch, especially pizza.
A few years and one move ago, I created a WFO after watching this video:

I actually made it “permanent” in my yard.
For the base, I used a cast iron coffee table with a ceramic tile top. I got several hundred fire bricks for $40 from someone who was rebricking a chimney. I put down a double layer for the base, double layer walls and a double layer ceiling. It worked great for several years. I kept it covered and protected with a tarp when not in use.

When I moved into my current house, the hubby did not cover the firebricks before I rebuilt my oven and so they got wet and have gradually been disintegrating. Summer of 2019, I had pieces of brick flaking off inside the oven when I was cooking so I had to close down the oven.

For two years I have been trying to muster up the courage to put in a real WFO. I just can’t do it. I had to accept I just don’t have the skills, money, or energy to do it but I miss my pizza parties. My friends keep asking me when they are going to start up again.
I want to try something a little different so I found this video:

I am going to use the coffee table base with the double layer of firebricks. I think I have enough firebricks for the interior layer of both the firebox and the oven. For the outer layer, I am going to have to use bricks from my patio. These are red bricks from the 50s. I am not sure what they are made of. It doesn’t look like concrete because they are very smooth.

Here is my question: I want to make the oven 28-30 inches square on the interior so the 24-inch concrete used in the video won’t be big enough. Do you think I can cast a slab using the ‘home brew’ mix from David S AND embedded either rebar or hardware cloth that the cast slab would be strong enough to span the 28-30 inches?

Any suggestions on how thick to make the slabs for the oven floor and ceiling?
I am a physics teacher—spring break is coming up in a few weeks and I would like to make it then so it can fully cure before summer pizza party season.

Second question: where do I get SS needles and polypropylene fibers?

Thanks for any advice.

Barb

[Pizzarotic]

Here is my question: I want to make the oven 28-30 inches square on the interior so the 24-inch concrete used in the video won’t be big enough. Do you think I can cast a slab using the ‘home brew’ mix from David S AND embedded either rebar or hardware cloth that the cast slab would be strong enough to span the 28-30 inches?

Hi Barb,
It's a bit confusing what you are asking? You say you are building the oven on a cast iron table. What does the slab have to span of it is sitting on a base?

Home brew is not for casting a slab base, you would use normal reinforced concrete for that.

If you mean you will be casting the oven floor than yes, you could do it with home brew mix but not ideal way to go. Thickness for oven floor and shell would be 2" and you would not use any type of reinforcing in the oven floor or shell other than the SS needles.

[Pizza2Night]

Hi.
Thanks so much for responding. I agree the post was confusing without the youtube videos. They were not advertising anything but were removed making the post unintelligible.
I am making a pizza oven shaped like a box that has two parts:

Stand: Iron coffee table
Fire box on top of stand:
Floor: two layers of firebrick,
Sides and back: inner layer of firebrick; outer layer of regular brick--both are four bricks high
Front: open
Top: concrete slab that I want to cast

Oven directly on top of firebox:
Floor--top of firebox
Sides and back: inner layer of firebrick; outer layer of regular brick--both are two bricks high
Front: open
Top: concrete slab that I want to cast

There is a gap between the back wall of the firebox/oven and the firebox/oven slab that pulls air up through the back, over the pizza, and then out the front:









People who build this (there are a lot on youtube) use a 24x24" concrete patio tile from a big box store. I want a big floor for making pizza (I have a lot of friends).
We make individual 6-inch pizzas and so I usually cook three or four at once (I made a lot with my old oven so I am pretty good with a peel). I really need the wider span.

One more addition--in the ceiling of the oven, I plan to put a chimney (or at least an opening) in the front to try to mnimize smoke going right out the front--that was a problem with my old design. I got pretty smoky while cooking.

SO, will the home brew work on a wider span? I am especially concerned about the ceiling of the firebox.

Thank you!!!!

[UtahBeehiver]

I suggest you download the "free" eplans from Forno Bravo and review the design section. You will see the a hemisphere is the most effective shape for a WFO oven. A cast oven in this spherical shape can be done relatively easily and cost effective. Insulation under the floor and on the dome can be accomplished with a vermiculite or perlite/portland cement mixture (5 to 1 under floor, 8 to 10 to 1 over dome).

As for hyperlinks, we as moderators have to deal with dozen of spammers and hackers daily and some have been successful in corrupting the blog to the point where members have lost posts and threads and have forced the blog down, so we are very careful about allowing any hyperlinks.

[Pizzarotic]

SO, will the home brew work on a wider span? I am especially concerned about the ceiling of the firebox.

Yes, it should be fine at 30" wide, but I would be concerned about using steel reinforcing in the slab. The reinforcing will expand far greater than the concrete does and cause the concrete to fail, so cast it without reinforcing. It would be fine to add angle iron supports under the slab (front and back) as additional support if you choose.

My other advice would be to just use plain bricks for the Firebox floor as they will handle the temperature just fine and save cost. Also insulate between them and the table with a couple of inches of vermiculite & cement 10:1 mix.

Also use a thin layer of fire bricks for the pizza cooking floor on top of the slab,. That will increase the thermal mass and also stop contamination of your pizza's from the concrete slab.