Trying a thin Dome Pompeii?

[Xabia Jim]

I wondering about making a thin domed Pompeii for just pizza using the thin firebricks. What's your thoughts about using a thin (3cm or 1.2 inch) firebrick.

I'd consider it experimental and am thinking about using just a gypsum cement as well. Probably cover it with another gypsum/sand/cement layer when complete for some more structural support and weatherproofing.

If a thinner (low mass dome) is good for pizza, (vs high mass bread/roasting oven, which I have already) then a very thin dome should work...

Any experience/thoughts/suggestions?

[noosab]

I'd worry about the refractory properties of gypsum and the spall properties of the blend.
Earl

[Marcel]

Hi, Earl,

How are your reeds, or don't you play the bassoon?

Ciao,

Marcel

[dmun]

Originally Posted by Xabia Jim

I wondering about making a thin domed Pompeii for just pizza using the thin firebricks. What's your thoughts about using a thin (3cm or 1.2 inch) firebrick.

In the US the one and a quarter inch thick firebricks are called splits, and they are the same price as full thickness (2.5") firebricks. I've used them to line the firebox of an old fireplace where space was at a premium, and they cut really easily. Also, at that thickness, firebricks cut really easily, and you don't need the 10 inch wet saw to cut them, other than to save your lungs. In addition, a dome that thin could use a minimum of mortar, which combined with the easy cutting of shapes could give you a really good looking dome.

On the downside, you would have to use a premium refractory mortar. A dome that thin would have much less tendency to self-support when, and if, it cracks. You say it's an experiment, but you still don't want it to end up in a heap on the hearth floor

I'd consider it experimental and am thinking about using just a gypsum cement as well. Probably cover it with another gypsum/sand/cement layer when complete for some more structural support and weatherproofing.

Gypsum cement? like drywall joint compound? Wow, no. It cracks like the desert floor at any thickness, and has absolutely no heat resistance. I know that people build ovens out of mud, and use them for a few firings before they begin to fall apart, but why would you want to? Unlike a failed mud oven, you can't just hose the mess onto the lawn when it collapses.

[noosab]

Originally Posted by Marcel

Hi, Earl,

How are your reeds, or don't you play the bassoon?

Ciao,

Marcel

Hi Marcel,

My reeds are fine, but my playing is amateurish. Don't have much time to practice now that I'm retired. Oh, yeah, I don't spell bassoon with one S, but that's how it turned out when my wife's ex got me started with yahoo and tried to spell bassoon backwards. Do you play?

Ciao,
Earl

[james]

Hi Jim,

I think the split might get your orientation wrong. When you cut a standard brick either in half, or thirds, you have enough volume left of the brick to do a nice job of stacking them to get your nice dome shape.

It turns out that my indoor oven is a Scott barrel vault with splits, but with splits on their flat side. We used forms to hold the splits in place, then encased the whole oven with 5" of concrete. Looking back, that gives me a 1 1/2" oven face of firebrick, backed with a huge amount of very inefficient concrete. Not a great idea.

I think if you are looking for a nicely proportioned oven for pizza cooking, where your oven dome and floor can be fully fired in an hour or so, a 2"-3" dome of firebrick, surrounded with high efficiency insulation is the way to go. The firebrick will do a good job of absorbing and holding the heat of the fire -- and give you the 700ºF-800ºF you want for real Italian pizza.

Helpful?
James

[christo]

Have we heard a progress report lately from the person that built the pompeii with 1/3 thickness bricks?

Any measurement on heat up time or how it's doing after many heat cycles?

searched for third and 1/3 but the engine would not search.....

I'm curently between Dmuns geodesic and the 1/3 brick thickness with refrax.

Christo

[johnrbek]

Xabia,

I'm confused... Can you clarify? If you used splits (1.25" instead of 2.5" brick) cut in half, you wouldn't necessarily have a thinner dome... were you thinking of cutting the 1.25" splits in thirds for a 3" thick dome? Or, were you thinking of cutting a standard 9" firebrick into 1.25" pieces?

If you were referring to splits, as dmun mentioned, I actually think the idea of using the 1.25" splits is kind of interesting... I think I'd go cut in half for the same thermal storage as the standard pompeii though..

From what I've read and seen, the splits might even give you a more stable dome with less of a mortar gap than the 2.5" bricks would.. take a look here: French Bake Oven Workshop with Norbert Senf - 2003 MHA Meeting These guys started off in standard firebrick, then went to splits as they hit the curb... there a few really interesting pics... seems like there's less of a mortar gap using splits, which they refer to in the link.

It should be noted though that you'd be venturing out of Italian territory and into French... it seems like these splits are more common in that type of oven. Not sure if that matters to you or not..

Like the others I'd stay away from the gypsum stuff... you can go cheap using James mortar recipes... there are a couple of them I think.. Rado Hand has a similar recipe, though I think he augments it with a portion of lime..

Question for Dmun: you mention that a dome that thin would have less tendency to self support... again, I'm unclear as to how Xabia would be using the splits, but if here were cutting them in half, wouldn't he have the same stability (or more?) as with standard 2.5" firebrick?

Later..

JB

[james]

John,

That's in interesting point. You are describing cutting, and laying the splits on the flat side -- so again you have control over how thick the dome is by whether you cut the bricks in half, or thirds. Still, you would have higher dome costs, as your bricks are thinner, and the cost about the same as a standard firebrick.

On the French oven, that's a fun point. The french oven uses a thin, pressed "bread bakers tile" for the floor. I wouldn't do that personally, as I think it is too thin, and I think they end up setting it on some concrete to get more mass. 1 1/4" on the floor it too thin. For that you would want a standard brick on its side -- for about 2 1/2".

On the mortar, we have settled on a 1-3-1-1 recipe that does have lime as well -- and that recipe should be everywhere in the plans. No more cost, and a little easier to work with. 1 part portland, 3 parts sand, 1 part fire clay, 1 part lime. Let me know if you find anything different on the plans.

James

[dmun]

Originally Posted by johnrbek

Question for Dmun: you mention that a dome that thin would have less tendency to self support... again, I'm unclear as to how Xabia would be using the splits, but if here were cutting them in half, wouldn't he have the same stability (or more?) as with standard 2.5" firebrick?

I misunderstood. I thought Xabia Jim was proposing to build an oven with splits laid up ON EDGE, so as to get a very thin dome with quick heat up. I envisioned this wonderful egg-shell thin dome, my comments about stability refered to the thinness of the dome. If he were planning to lay them up flat, as in the french oven refrenced in the last quote, then it would be as stable as can be.