Wire mesh

[rick]

1) My ovendesign started out as a Breadbuilders oven, transformed later into a Pompeii oven. I skipped most of the mass in the design but still have more mass than most of the Pompeii ovens shown on this forum. I have a 6" floor (3.5" concrete layer + 2.5" firebricks ) and I just finished the dome which is now 4.5" (firebricks). I'm planning to add another 1.5" of cement/sand/fireclay mixture (the same I used for brickmortar) to make sure that the dome and floor are of equal thickness. Because 1.5" inch is quite a thick layer I am considdering applying a thin wire mess in the middle of the layer.

Any comments on the thickness of the dome or the use of a wire mess? Is it easier to add the wire mess first and than add the mortar? Or should I first put half of the mortar, after that the mess and after that the other half of the mortar?

2) The oven I build will be Iglo shaped. In the Pompeii plans there is a description on how to do this. The advise is to use 2 thermal blankets for isolation of the dome. Is this really nessecary? I was thinking on using only perlite (4").

Thanks upfront for your help.

[CanuckJim]

Re: Wire mesh

Rick,

I think the pour should be in one go, with the mesh in postition, wired together to keep it in place. The blankets will give you better heat retention than vermiculite or perlite. You will have more mass than most, which means your heat up times will be longer, but the retention of that heat will be longer, too. It really depends on how you intend to use your oven: strictly pizza, or a lot of other things, too, like BREAD .

Jim

[james]

Re: Wire mesh

Hi Rick,
Think of the insulation guidelines in the plans as our recommendation:

1" Insulfrax/4" vermiculite, or
6" vermiculite, or
2" Insulfrax

You can get by with less; the only issue is that your oven might get a little hot on the outside enclosure, and that you lose a little heat in the oven. If space and budget aren't a big issue, I always think that a lot of insulation is a good thing. If either is a little tight, you can cut back some.

Hope that helps.
James

[maver]

Re: Wire mesh

Rick,

That concrete layer under the oven is pretty thick - I would be concerned about ability to reach a good pizza temperature on the hearth (I'm envisioning burnt cheese and little browning of the bottom of the pizza). I don't know that increased mass in the dome (to equalize the dome and hearth thickness) is a good idea. If I was doing it over again I might go thinner all around. In your case, I wonder about keeping the dome thinner so it heats up faster and radiates heat to your hearth to bring the hearth temp up faster.

This is all speculation, but I know I have plenty of heat retention for home use for bread and slow roasts with my oven. I have firebrick sitting directly on the perlcrete, then 4.5" dome with about 1/2" of cladding all around. If I could shorten my heat up time to under an hour it would save me wood and increase convenience. I wonder if anyone who built a thin dome oven has any data on heat up time to report?

[DrakeRemoray]

Re: Wire mesh

I think Maver has good points, but Jim's question is most relevant. How do you plan to use your oven? Are you planning on mulitple bakes of bread?

Drake

[maver]

Re: Wire mesh

Drake, you're right, that question is central to how to build it. I'm just wondering if you can make up for a big heat sink in the hearth by having a more rapidly heat saturated dome. My guess is that by increasing the dome cladding you just compound the problem. My user experience with my oven makes me in interested in how a thin dome would perform (perhaps with 2" ceramic blanket to try to stop heat loss), even though I can start pizza in about an hour.

[rick]

Re: Wire mesh

Hi guys, thanks for the input.

Before I began building my mind was completely focussed on a Scott oven. It should have become 8" all around, which is advised as a minimal thickness (I know, I know, still way to thick for a homeoven). Just before building I realised that the long firing was a problem for me. I had to change my mindset but I was afraid to come all the way down to Pompeii thickness, mostly because I'm more into bread than pizza. That's why I choose 6" which would/will make it more of a hybrid. I guess (stories on this forum tell me) that I could have applied even less mass because one large batch of bread will suffice. For me, this point is a point of no return though.

What I still am curious about is the domethickness/floorthickness ratio that Maver addressed. For the Scott oven this ratio is (just under) 1. In the past I had contact with Jim Hatch and he also advised me to go for equal thickness in dome and bottom as the best compromise for pizza and bread. Not that an inch more or less made any difference in his opinion. More recently build Pompeii's have a much larger ratio. F.e. the ratio in Mavers oven is 2. This maybe excellent for pizza but in case of bread I can imagine the floor will be overhot compared to the dome. Any more comments on that?

I'm pretty thickheaded so up to now I'm not convinced that keeping the dome 4.5" will solve the "burned cheese/little browned bottom" problem. This will make my ratio .75. Maybe the problem will even get bigger because it will take longer for the bottom to heat up. Heat from the ovenfloor will sink causing the floor to cool down faster than the dome. As a result I would have to reheat the floor between rounds of pizza. Or will this only occur if the oven is not fully saturated?

By the way: for me this is all speculation because I have no live data. So please feel invited to overload me with your experience.

[james]

Re: Wire mesh

Hey Rick,
The question almost seems to be whether it is worth putting more (too much?) mass in the top of the oven in order to keep the ratio between floor and the dome around 1:1. That's a really interesting trade-off. I think your comment that an inch either way in the dome isn't going to make a huge difference is good one. I don't think that adding more mass to your dome will make it easier to keep your oven in balance when you are cooking, and your current 4 1/2" dome will hold more than enough heat for baking. So I guess my vote is to not add much more on top.

One thing you can do when you start cooking pizza is to maximize how you drive heat into the cooking floor. Talking with the Modena designer, I learned that your cooking floor recovers heat lost from cooking in three ways.

1. The fire drives heat across the floor.
2. The flame bounces heat off the dome onto the floor -- where it is absorbed. This is huge.
3. The heat stored in the cooking floor, below the top where you have cooked, rises back. If your floor is fully saturated, it does a better job of this recovery.

My experience with thicker cooking floors is that you have to work harder with your life fire to keep the floor from losing its heat after a couple of pizzas.

Hope this is helpful.
James

[maver]

Re: Wire mesh

F.e. the ratio in Mavers oven is 2. This maybe excellent for pizza but in case of bread I can imagine the floor will be overhot compared to the dome. Any more comments on that?

...Maybe the problem will even get bigger because it will take longer for the bottom to heat up. As a result I would have to reheat the floor between rounds of pizza. Or will this only occur if the oven is not fully saturated?

Rick, I have scorched the bottom of my pizza only when I cooked at hearth temperatures around 900 degrees (and I think I was using all purpose rather than caputo flour - the flour may have been more the problem than the temp). My oven floor is never hotter than the dome. I expect you will encounter a longer heat up time due to the thicker hearth, but I don't know how much longer. However, the dome at 4.5" will be more than enough to bake a large batch of bread (my oven does this just fine - I have to wait about 1 1/2 hours with no coals for the oven to cool enough after pizza - at least an hour with the door off, then replace the door to moderate the temperatures). I don't know how practical it will be to get your hearth fully saturated with heat but expect that with a good fire you'll manage ok.

James' second point from the modena oven designer is why I was speculating on keeping the dome thinner to improve your hearth heat up. As a home oven user, I think one of the biggest issues for practical use is to shorten the heat up time.

[james]

Re: Wire mesh

Maver,
I think your point on heat up time is a very practical one, and a good way of thinking about it. If you can get your oven up to heat faster, you will end up using it more -- like after work on a spring or summer mid-week evening. As a real-world example, the Casa ovens are a little more than 2" in the dome and floor, and you can bring one up to heat in as fast as 40 minutes in a pinch (that's pushing it, but you can do it). If you fire a Casa longer, it will easily hold enough heat to bake an oven full of bread -- or 2-3 batches of smaller amounts amounts of bread. It seems to me that for a lot of users, that it what you are looking for. I am definitely not pushing the Casa ovens, but rather the basic design -- and whether it is something you want to use as a target if you are building a Pompeii oven.
James