Bricks over angle-bar scaffolding?F

[gigelus2k20]

Hi,

I'm working on a pizza oven and grill combo (deeper cavity for grilling, with multiple grill height positions, and removable half-brick floor over angle-bar mesh placed at the highest grill setting as pizza oven).

My question is about the dome construction. Because I want to avoid an excessive thermal mass, my plan is to make the dome primarily from half bricks (9x4.5x1.25) placed horizontally. With such a thin dome, arch-based construction is not possible, hence I was thinking about creating a scaffolding made from welded angle iron. The bricks would sit tightly on it (no need for room for expansion as the angle bars will expand more, and a perlite/portland cover over these bricks, including the V grooves from the round ceiling.



Long time ago, I saw on youtube something like that being built, but I can't find that video anymore. Has anyone on this forum tried this method?

The primary reason for why I'm looking at making a thin dome is minimizing the burn time to get the dome to 700F (I'm not as ambitious to expect 900F). My other oven, which I built 8 years ago based on the instructions from the fantastic "The Bread Builders: Hearth Loaves and Masonry Ovens", is working very well for bread baking, but it takes 4-5 hours of continuous burning to achieve 600F and I can't do grilling in it.

Before anyone is asking, the location of the chimney is optimized for grilling, with the vent being closed with a brick slid from the back when the oven is used for pizza; I don't mind the smoke when the pizza oven is heating and once you get to 600-700F you don't get any smoke anymore. I also am planning to create a free-form front "lip" from castable refractory cement to drop the opening to the required 62-65%.

[gigelus2k20]

In case it was not clear what I have in mind, this work in progress photo should explain better:

[david s]

Because your system will be an updraft one with the flue location at the back, then it won't operate in the same way as the cross draft system like the tried and true hemisphere with a front flue. The flame will tend to jump straight for the base of the flue rather than following the whole of the inside of the dome , down and exiting the front by which time there's next to no wasted flame going up the flue.

I think also that you are going to have trouble maintaining floor heat for pizza cooking as your floor is not insulated under.

If you want to make the walls thinner you could consider casting it as most cast ovens are around 2" thick.

You will also need to brace your walls at the base of the vault as the outward pressure exerted there threatens the structural integrity of the build.

Barrel arches end walls should also be built under the vault rather than against it because the expanding vault has a tendency to push the end walls out. This is another reason for steel bracing on the outside.

Lastly, what happens when the heat corrodes those steel supports? They will be extremely difficult to replace.

It also appears that you've left minimal room to insulate over the oven.

Not wanting to rain on your parade, I love designs that push the envelope, but people have been at this for thousands of years as everyone has to eat and cook and pretty much every variation you could think of has been tried.

[gigelus2k20]

Hi David,

Thank you for the detailed reply.

The flue location in the back is for when the oven is used as a grill, directing the smoke up the 3ft long chimney. When the oven will be used as a pizza oven, a brick will be inserted from the back, completing the arch and closing the flue.

Regarding the hearth insulation, the bricks are mobile and are sitting on a removable rebar grid (the whole floor is taken down when grilling). You have a valid point, I will likely place an insulating layer on the metal grid, then drop the bricks on top of that.

About exterior insulation, I plan on covering the half-brick arch with a layer of perlite/cement mix about 2-3” thick. Will see if the sides need insulation too, it can be added later.

The side walls are interlocked with the back wall, I expect them to be robust enough to sustain the weight of the top, which is lighter than usual (chimney will be held by the back wall). The brace angle also projects a significant weight component downwards. The braces will be welded on two angle bars running front-to-back on the inside lip of the side walls, protruding behind the back wall and joined via a threaded rod for added strength. Have not found a way to further brace the front sides.

Metal expands much more than brick, I plan to keep the arch bricks un-mortared, and either insert slivers of brick to fill in the gaps or let the perlite-mortar cover deep into these grooves.

The big question is, indeed, how well will the metal hold over time. I don’t have a good feel for how fast it will rust, but, being 1/8” thick, I hope it will last at least 2-3 years. It’s an experiment indeed.

Cheers!

[david s]

Ok good luck, keep us posted. Here's a link that takes you to another thread for a barrel oven detailing the steel bracing I was talking about. It may help you with your design.

https://community.fornobravo.com/for...852#post406852

[gigelus2k20]

The metal framing is complete. Just a few more bricks to shape for the front arch, then mortaring the back and the chimney (which is made from half-firebricks for the first course, then clay pipes), then a shallow layer of mortar to seal everything off (fireclay, lime, Portland and perlite), then several layers of Forno Bravo’s ceramic blanket, and I’m ready to go... I hope

PS. I don’t know why the picture came on rotated...

[seannieboy71]

That’s looking great. I hope it works well. I went with a unconventional approach too. I have a flat roof supported by t-section steel. Like you, I hope to get a few years usage before the steel rusts through.

Keep posting pictures as you go. It will be fun to see how it turns out and how you deal with the challenges you encounter.