Oven floor insulator materials and process…

[david s]

Beware of granite, it does not like heat. If you do use it, make sure it is in a position where it can be easily replaced if it cracks. A crack in a granite slab can provide an easy pathway for water entry to the underfloor insulation. Regarding calcium silicate board as well as 5:1 vermicrete, the strength of both is not affected by water unlike mill board which goes all squishy when wet.

[mnagy]

Yes. I think I’m confused on the terminology there. I was going to have 1/2 bricks standing on their ends for the first course. And I was thinking they would be next to (not on top of) the dome floor. Then I can start with the indispensable. If I use vermicrete to insulate the upper/dome, is there something I can put on the outside of that (stucco maybe) before tiling?

[Gulf]

Mnagy,

Take a breath and quit designing. Go back and read this thread from the beginning. Remember that you said,

I’ve got all winter to look through these build threads, and will certainly take your advice.

,
I'm going to hold you to that! You will be a much better oven designer when you have read through the free plans and have read through several build threads

[UtahBeehiver]

Plus one of what Gulf said. Here is a link to some of the more documented builds on the blog.

https://community.fornobravo.com/for...n-the-archives

I am also going to move this thread to "Pompeii Oven Construction" rather than Tools.

[JRPizza]

mnagy, did you tell us how big of an oven you are planning on building? I looked but did not see it mentioned.

[mnagy]

19” inner radius

[mnagy]

I hear you Utah and Gulf. I’ve got all winter. Just getting excited. And I’m an engineer who loves sketchup. So when all you have is a hammer, everything looks like a nail.

[JRPizza]

That's a nice size. We built @39" ID and are really happy with the size. Have you figured out your placement on the hearth (fore/aft)? I used Freecad to lay mine out and it was really helpful as I built on a corner.

[mnagy]

My stand is a 3 block square (about 49” side) and my currently plan is to have the dome center just 1” aft. 38” inner diameter and ~56” overall diameter. I’ll have bricks around the entire stand which will bring the stand to ~58” sides (dome should be 1” from the stand sides, and flush with the back). In the front the outer dome (theoretically) would be 2” from the end of the stand, plus another 2” lip I’ll add with decorative granite or something.

I see a lot of DIY ovens with much longer entry tunnels, but pro ovens seem to have a front that doesn’t stick out much from where the dome would fall.

mall subject to change. I’ll make a build thread, and maybe even a you-tube video. As soon as we’re consistently above 40, I’ll get to work. Probably April.

I like they you have a roof over yours. I don’t really have that option. Gonna have a nice custom cover made for it instead.

[JRPizza]

Entry tunnel length can indeed vary quite a bit, and the large variations are obtained by type of construction (forgive me if you already have this sorted out). A cast or even welded vent can facilitate a very short entry, whereas bricks are typically 1.5 bricks (~13") long with some variation on how they tie into the dome etc. Have you a method/length in mind?

[david s]

Brick oven builds generally also have a flue gallery built with bricks, as in the Pompeii brick build plan. Unfortunately this leads to a deep entry which has the disadvantage of being heavy and the flue gallery therefore acting as a heat sink, drawing heat out of the dome and therefore requiring higher fuel consumption. Additionally brick units do not lend themselves to creating curves let alone compound curves. I think the tradition of brick building to use a brick flue gallery comes from having more bricks available than is required for the dome as well as wet brick saw on site, it seems logical to continue the build with brick.
A flue gallery built in steel, or cast refractory can be thinner, lighter and shallower than one made in brick. This means better efficiency and far easier working of the oven, allowing better access and shorter handled tools.
If fabricating in sheet steel it should be stainless and at least 0.9mm thick. If cast it can be done with either homebrew castable or proprietary castable refractory and probably no thinner than 25mm,

The attached link and pic provide some ideas.

https://community.fornobravo.com/for...723#post435723

[mnagy]

Lots to think about there, thanks! I don’t have anything figured out completely, but I needed to make a square stand, so I’m gonna have a much shorter entryway. I really only have about 6” beyond the outer dome footprint. My plan was a metal chimney attached to a custom fitting (which goes from a square brick opening to a round metal chimney).

[david s]

A square brick opening will result in a deep entry. The same cross sectional area can be achieved by a narrow rectangle, leading to a far shallower gallery. If the area at the base of the gallery is larger than at its top where it joins the flue pipe, a smoother smoke flow and extraction results.

[Gulf]

I was concerned from the beginning that you were going to have some issues with having enough room for even a shallow entry. I figured then that with some research that you would find that out. But, since the cat is out of the bag, here is one more thing to consider. That would be an ergonomic working height for your finished oven floor. Most recommended is the bend of the elbow while working the oven. I actually like it a little higher. I recommend the xiphoid process. My old back doesn't like working in a bent position. For me, the bend of the elbow would be 42". I'm guessing again from the pics that you are going to end up with about 38"? I'm just throwing this in to give you some things to think about when designing in elevating insulation from the hearth floor and possibly cantilevering fore or aft for your entry if needed.

[david s]

A square brick opening will result in a deep entry. The same cross sectional area can be achieved by a narrow rectangle, leading to a far shallower gallery. If the area at the base of the gallery is larger than at its top where it joins the flue pipe, a smoother smoke flow and extraction results.

This pic might explain better what I was trying to say. Design B will have a much shallower gallery as well as a better performing flue than design A.
+1 on Gulfs obsevation. The foundation slab may also be interfering with you being able to get close enough to the oven.
The Valiorani oven pic I posted in #26 I built on a circular supporting slab, so it is possible to do the same on a square footprint with considered design input.