My Cast Refractory Oven Build Other Oven Types Discuss My Cast Refractory Oven Build in the Pizza Oven Design and Installation forums; Originally Posted by cynon767 What kind of insulating concrete did you use for the underfloor? It seems like 2 inches ...

[JoeyVelderrain]

Originally Posted by cynon767

What kind of insulating concrete did you use for the underfloor? It seems like 2 inches might not give very much insulation unless it is of a very high r-value material, like the insblock or FB board people here are using. The perlite-concrete insulating mixture from the pompeii ebook is recommended for 4+ inches.

I used the perlcrete mixture.
You're right. I am now pretty sure I will get some 2" fiber board to place on top of this slab and under my bricks to get the 4" insulating layer... I will end up with 4 1/2" under my bricks actually.
thanks for the heads up.

[mr g]

Hi Joey, I wouldn't mortar the bricks down so that any cracked or broken bricks can be replaced. Why not use the fireclay and water mixture under the bricks to help get them even?
Cheers
Mr G

[JoeyVelderrain]

I am not mortaring the bricks down, I decided the path of least resistance was just to use my bricks on their sides instead of flat this gave me the inches of insulation I needed.
Surprisingly my perlcrete base turned out really smooth so not to many bricks stick up above others but the ones that do Mark suggested I could just grind down so I am not going to be using the clay mixture underneath.
The way I designed the side angle iron is so that they are spring loaded so the bricks fit rather snugly. You can see in this picture how I had to pull on the side to make room for the bricks, when I released the puller the side sprung back in shape. I also used a rubber mallet on the bricks as I put them in to tighten them up. The spring sides will allow for expansion also.


It is hard to tell from this angle but I ran out of bricks before I could finish. I am six bricks shy...I was never good at math


now the part we have all been anticipating (and dreading ) putting the 600 pound dome on top!!

[shuboyje]

Joey,

I think your project is great, and I would love to have mobil oven of my own. But, personally if it where my oven, I would be even more concerned about the floor them before. The firebricks are thermal mass, not insulation. You have now made your floor very massive by turning the bricks on their side, and still done nothing to add to the insulation under floor. I think you will struggle to get this hearth up to pizza temp's, and I bet others will chime in shortly with the same thoughts. Best of Luck whatever route you choose to go.
-Jeff

[jmhepworth]

Joey,

Where's the insulation? Don't start building the dome yet. You need insulation under the floor or it won't work .

And don't dread building the oven. That's the fun part (other than eating pizza, of course).

[JoeyVelderrain]

so it sounds like I can't get away from adding another 2" of perlcrete to the base does it? I guess I'll just bite the bullet and add the perlcrete so I don't regret it later.

[jmhepworth]

I would also re-think having the floor on their edge instead of flat, particularly with a mobile oven. You want to get in, fire it up, cook pizza, and get out. Those of us with stationary ovens can often afford the time it takes to heat up the oven. Laying the bricks on their side will more than double the mass, so it will take considerably longer (and more wood) to heat the floor to 750. I thought about laying my floor the way you are planning but reconsidered after listening to the experts on the forum. The only good reason to add the mass is to cook commercial quantities of bread. Do you really plan to do that with a mobile oven?

[Mitchamus]

The flip side of the coin,

is that with a high volume oven, you would want more mass in the floor, as this is where you will be doing most of the cooking, and be sapping out most of your heat.

Telling your customers to wait while you rake the coals back over the floor for 5 minutes to heat it back up isn't really an option.

No-one on here can accurately tell you how much longer or how much more fuel it takes with a thicker floor. (in a quantifiable measure) as no-one has tested two identical ovens side by side.

It's all speculation. - and what you will need with this oven, is a constant heat from the floor, with the ability to cook all day.
I would rather spend an extra hour on the heat up time, if it meant that over the course of cooking 100 pizzas I didn't have to re-charge the floor every 5 pies.

what you want is a stayer - not a sprinter.

Don't be afraid to deviate from the norm.
(please note - this is my speculation also!! )

also - you'll only be increasing the mass by about 30% since bricks are only about 30% higher than they are wide.

[JoeyVelderrain]

I think the best thing will be just to add the extra 2" perlcrte and leave the bricks like I have them that way i can cover all my bases.

thanks guys, I'm glad this came up before I put my dome on top.

[jmhepworth]

I like the look of the bricks on edge. Will you position the oven so that the floor is herringbone? That would make the oven angle toward the wheel, so that might not work. I doubt you want to do all of the cutting necessary to put them at a 45 degree angle. Let us know how the oven performs. So much of what we talk about is just theory until someone tests it. I'm interested in seeing how much time it adds to heat up.