Another curing question

[pmgnut]

So the issue there is heat loss im assuming

[UtahBeehiver]

The oven structure should be isolated from touching the concrete hearth. The floor on you oven is isolated but I am talking about the oven walls. By having the walls touching the concrete hearth, heat from the dome or barrel will transmit down into the concrete hearth unless it is insulated from the hearth.

[pmgnut]

Not sure what you mean?

[UtahBeehiver]

I see the floor insulation but I cant see the barrel structure to see what is under the first course. Why I asked, I did look at the YouTube video and it shows the barrel bricks mortared direction to the concrete hearth. This YouTube video is right on the borderline of being a commercial hyper link promoting a product so it would be normally not permitted.

[pmgnut]

yes if you look in the pic just underneath the oven floor, you can see there is a 5 1/2" thick vermiculite and portland pad

[UtahBeehiver]

is there insulation under the first row of the barrel or do the bricks sit directly on the concrete hearth? if the latter, there will be quite a bit of heat loss since the hearth will act as a heat sink. Just something you need to be aware of. Nothing you can do now about it.

[pmgnut]

Yes there is a square hole i did leave on top of the arch for a chimney {its not visible in the picture}. Fire will be against the back wall, then pizza. I'll also do either a smaller arch in front or make a removable door to put in place to keep some of the heat in, or both.. So it sounds like i should go the extra step and add a blanket of ceramic insulation. Do I need to put poultry wire on top of the blanket before i begin laying the red bricks?

[Sixto]

Ah, I thought you were building a dome with an arched entry. I really don't know anything about barrel vault ovens, but the same insulation rules probably apply. If you end-up without any insulation and you just add another layer of red brick, you are heating up twice the amount of mass (2 layers of brick) which will take longer, and the outside face of red brick might get up to 500 degrees or more (burn risk?).

Another point is that there is a common saying that "all brick ovens crack" from thermal shock. If you don't have any insulation, the cracks may go all the way through both brick layers.

P.S. I saw the video and edited my response since the video answered most of my questions... I would ask the people who posted the video. I would love to see photos and read about how the oven works when you finish it.

[pmgnut]

Here is how I did Ii by shaping the brick on top to only have 1/4" gap...See the bottom photo on post #61. https://community.fornobravo.com/for...olis-wfo/page6
also see post # 94 for a front view... I only used 1/2" fiber blanket between the two arches, and then compressed a 3/4" rope gasket at the front edge.

It can be done!

Ahhh I see what you did. Very good looking oven, fantastic job you did. My son and I really need to keep expenses down at this point so if the layer is not absolutely necessary then I may skip that step and lay red common brick right over the arch. Basically we are building the oven very similiar to this one which doesnt show adding an insulation layer. https://www.youtube.com/watch?v=OKPqnlXAViI

Here is a picture with arch done just before we removed my makeshift 55 gallon plastic half barrel template.

[Pizzarotic]

So if I put 1" of insulation, how do I hide the super wide joint that it would create on the front face??

Some use a decorative fascia on the front of the arch that covers the insulation layers. You can leave the arch uninsulated without causing any issues which is my preference, I like the brick look.

[Sixto]

. So if I put 1" of insulation, how do I hide the super wide joint that it would create on the front face??

Here is how I did Ii by shaping the brick on top to only have 1/4" gap...See the bottom photo on post #61. https://community.fornobravo.com/for...olis-wfo/page6
also see post # 94 for a front view... I only used 1/2" fiber blanket between the two arches, and then compressed a 3/4" rope gasket at the front edge.

It can be done!

[pmgnut]

thanks for the info! The thing is, my son won't be cooking pizza all day or weekend long. 4 or 5 pies at best on a weekend. So my concern was not so much for the insulation factor, but more concerned if it would open a chance for cracking the firebrick arch which is what I really need to avoid. So if I put 1" of insulation, how do I hide the super wide joint that it would create on the front face??

[Sixto]

Congratulations on completing the arch!

Many people build with no insulation, and typically, their rationale is that they don't care about retaining heat for the next day in the oven. In my opinion that is shortsighted, if someone is already making Pizza dough, one might as well bake some bread on day 2... and roast a cut of meat or veggies on day 3....In the scheme of an oven, insulation is rather cheap and lasts forever.

The second more practical reason for insulating is that it evens out the heat load for the firebrick, and avoids thermal shock which can cause cracks in the inner dome layer.

How much insulation is up to you, 1" plus redbrick might be enough to avoid cracks on the inner dome..the temperature of the outside face of the redbrick layer may get to 300f or higher, though. Many people buy one or two 25' rolls of 1" ceramic fiber blanket. I got 4 " of insulation on the top half of my dome and 3" below that from two rolls 'cause I do plan to bake on day 2.

[pmgnut]

Hi all, Firebrick arch is now completed as well as the back wall. I used high heat mortar in all the joints. I now plan on topping off the entire oven/arch with red common brick and my question is , is a layer of ceramic insulation blanket absolutely necessary first? [ it would be sandwiched between the firebrick arch and the common brick outer layer} meaning, can i simply begin laying my red common brick right over the firebrick? Or is it critical for an airspace in between the layers?

[david s]

Depending on the thickness of the vermicrete and the weather of course, but it should be dry enough to proceed safely. Using a cheap garden moisture meter is a useful device. The surface of the vermicrete may appear dry and white, but moisture deeper in takes way longer, just like a pile of sand which dries out in a day or two on the surface but takes months to dry deeper in.
Before the advent of the newer (and more expensive) generation of ceramic fibre blanket that is exonerated as a carcinogen, I bypassed it in preference to using 10:1 vermicrete (around the same insulation value). I found that a thick layer of 70mm just didn’t dry because it was too thick. To solve this problem I used to do two 35mm layers with a week to dry after each layer before proceeding.