Not much here in the way of guidance for smaller ovens (28inch internal or less)

[UtahBeehiver]

Typically the best placement of the pivot point on the IT is at the brick floor elevation. So if you have a 33" ID oven at floor level or 16.5 " radius, then the dome will also be 16.5" from the floor level at the top of the inside of the dome. If you chose to have a different internal height at the top of the dome vs the radius at the floor level then you will either have to raise the IT or adjust the radius of the IT as you go up. You cannot have both. I am confused by what you said in you edit on using a shiner instead of a stretcher, the cad drawing indicates a full soldier. I am looking at this from a using of a IT to build your dome. As noted by DJ, I mentioned that the arch design may require buttressing depending on the type of chimney you chose. Based on a brick chimney vs a SS steel vent buttressing of the side walls of the vent area is recommended.

[xizenta]

Typically the best placement of the pivot point on the IT is at the brick floor elevation. So if you have a 33" ID oven at floor level or 16.5 " radius, then the dome will also be 16.5" from the floor level at the top of the inside of the dome. If you chose to have a different internal height at the top of the dome vs the radius at the floor level then you will either have to raise the IT or adjust the radius of the IT as you go up. You cannot have both. I am confused by what you said in you edit on using a shiner instead of a stretcher, the cad drawing indicates a full soldier. I am looking at this from a using of a IT to build your dome. As noted by DJ, I mentioned that the arch design may require buttressing depending on the type of chimney you chose. Based on a brick chimney vs a SS steel vent buttressing of the side walls of the vent area is recommended.

Thank you Utah for your reply. I see where our measures were different for the dome height. I did my calculations assuming the first course of brick would stand proud of the floor by 2.5 inches, as would be common in most domes with a header orientation for the first course, then I added some extra height based on having a soldier orientation. In other words, my dome had the IT pivoting from 2.5" below the top of the soldier course. What you are suggesting, alternatively, is placing the pivot at the floor. I can do that. I guess I would even prefer it as it would result in a lower ceiling.

Regarding my previous post about the shiner vs a stretcher orientation, I was talking about the brick chimney. My cad drawing has a stretcher orientation, which would require something like 32 full size bricks to create a 2 foot long flue. I thought it might save weight if I reoriented the bricks so the chimney walls were 2.5" instead of 4.5".

Any links to suggest the design of buttressing for the sidewalls of the arch? If I can do that well, may as well go ahead and try to do the brick chimney.

Thanks bud.

[UtahBeehiver]

Have you factored in a clay liner for the chimney. Look at Gulf's chimney design. Are you enclosing the oven or not. If enclosing, I have seen builders placing a CMU butting up against the vent wall. If not enclosing, I have seen another brick wall butting up against the vent wall brick. If you go the second route, the second brick wall could also help support the brick chimney as well. There is a really cool brick chimney that was done recently, it is a spriral screw shape. Think it was done in the UK.

Although this comes out the top vs the front which is not the best design, you get the idea of the brick work

https://community.fornobravo.com/for...chimney-design

[xizenta]

Have you factored in a clay liner for the chimney. Look at Gulf's chimney design. Are you enclosing the oven or not. If enclosing, I have seen builders placing a CMU butting up against the vent wall. If not enclosing, I have seen another brick wall butting up against the vent wall brick. If you go the second route, the second brick wall could also help support the brick chimney as well. There is a really cool brick chimney that was done recently, it is a spriral screw shape. Think it was done in the UK.

Although this comes out the top vs the front which is not the best design, you get the idea of the brick work

https://community.fornobravo.com/for...chimney-design

Very cool spiral. No I was not planning to enclose the oven. I will think about this and try to design some brick buttressing for the arch walls.

I am really confused about the clay liner you mentioned. I think I know what you are talking about. Those clay flues which are like a half cylinder shape? Would I need that? I was planning to judge have a rectangular opening inside of my brickwork.

[UtahBeehiver]

Clay flue liners come in various shapes, round, square, rectangular. They are able to withstand high flue temps and also protect the brick mortar joints. Old school masons would parge the inside of the chimneys with refractory mortar for the same purpose. I was actually mistaken on Gulf's build, he did not use a clay liner.

[xizenta]

Clay flue liners come in various shapes, round, square, rectangular. They are able to withstand high flue temps and also protect the brick mortar joints. Old school masons would parge the inside of the chimneys with refractory mortar for the same purpose. I was actually mistaken on Gulf's build, he did not use a clay liner.

Roger. So if I construct the chimney with firebrick and the same mortar used in my dome, won't it also be able to withstand the temperatures? I thought that we were using refractory mortar anyway.

[Gulf]

Roger. So if I construct the chimney with firebrick and the same mortar used in my dome, won't it also be able to withstand the temperatures? I thought that we were using refractory mortar anyway.

That will be fine. The refractory brick and mortar don't need parging unless you have to smooth out the transition. (The borrowed graphic is similar to an old style fire place without a damper, but the idea for a smooth transition is the same for an oven) The old folks had to do it because they had to rack the brick in, as much as for switching to non refractory brick in the smoke chamber. The "heat shield" on the left in the graphic, is similar to where parge was installed to smooth out the flow. Nowadays the wet saw lets us work around this problem with out having to parge. That is, if you keep using fire brick or a good solid clay brick up through the smoke chamber. A refractory mortar is also best in the smoke chamber. That wasn't always so. Masonry cement used to be made with portland and hydrated lime. That would last for years in a firebox without repointing. Today's bagged masonry cement is made from portland and " the equivalent" of hydrated lime. (Usually crushed limestone and some proprietary ingredients) It wont hold up to time and high temperature.

[david s]

There is another fundamental point to consider with a small oven and that is the relationship between oven volume and wall thickness. When building with brick a wall thickness less than 4" (half brick) suffers from weaker bonds between units, that is why smaller ovens are better built with castable. Most castable ovens are around 2" thick. Most people think a smaller oven will heat faster, but this is not necessarily so. If you build a 24" oven with 4" walls it will be slow to heat up because the volume of the chamber and therefore the fire it can deliver to the floor and walls is smaller. Remember that while area goes up squared volume goes up cubed. My cast 21" oven with 2" wall and floor thickness takes an hour and a half to get to pizza temperature, much the same as a much larger oven with walls double the thickness.

[xizenta]

So fellas, I have built my slab out of 3" of reinforced concrete with about 3" of 7-to-1 Vermicrete on top. Now, I am concerned about water getting into the vermicrete due to rain, etc, and not draining well. Am I supposed to stucco the vermicrete slab before I build the brick floor and dome on top of it?

What are the pros/cons to stuccoing my whole base and slabs now (after allowing the vermicrete slab a week to dry)? Any downside to building the dome and pizza floor on top of stucco? I guess the alternative would be to build the pizza floor and dome first and then stucco the slab only in areas not covered by the dome.

[deejayoh]

Why do you want to stucco the slab? Stucco isn't waterproof or structural, nor does it provide any thermal benefits

[Gulf]

Deejayoh is right. You don't want to stucco the floor insulation. That will trap a lot of water in that would be very difficult to get out. Also, it would be best to wait as long as possible before building on the vcrete. The sooner you build on it, the more water that will be trapped under the oven floor, which will have to be delt with later during the drying phase. Just carve all the excess vecrete out down to the slab when you know exactly what you oven's rendered foot print will be. It wont be very difficult to carve. Protect it from the rain a;; through the build.

Just, for those future builders that are following this thread: It saves a little trouble if the vecrete is formed to shape before the pour.

[xizenta]

Gulf,

what would be the purpose of carving out the vermicrete from around the footprint? I haven't seen that done before. I can't leave it and stucco over it?

Also to the other gent that asked about why I would stucco, I just thought it would be nicer cosmetically and provide some water resistance.

[Gulf]

I haven't seen anyone carve it out either, except to anchor the bottom plates for an enclosure. I also haven't noticed anyone pouring the vcrete outside of the footprint of the oven for an igloo. I suppose it could be stuccoed over outside of the foot print of the dome. Provided that you contour the render from the dome over it and keep it sloping downward each direction to help shed water. Just keep it protected from the elements and don't stucco over it until it is dry or you will trap megga amounts of water.

[deejayoh]

So, just to be clear... concrete isn't waterproof. Neither is stucco. And vermicrete is basically porous, and will fill with water like a sponge. All of that water is going to wick water under your oven and keep it from getting hot.

I see you're in SoCal (from your profile) so maybe you'll be ok because it doesn't rain often. But the design of having the vermicrete extend beyond your oven and be exposed to weather is not a good one. Stucco over it may look better but it won't do much good for waterproofing. Maybe an acrylic stucco will. But not cement-based stucco.

FWIW, 3 inches of v-crete is not very much insulation. It's about the same as 3/4 -1 inches of CF board. That is less than half to a third of what most builds on this site are using. You might want to think about adding a couple inches of CF board (maybe I just missed that)

[xizenta]

Ok guys, here is what I have so far. I am going to try to use an inch of ceramic board on top of the few inches of vermicrete I have so far in order to make sure the insulation under the oven is sufficient as some of you have mentioned.

As you probably know, the vermicrete is really crumbly and doesn't hold together very well. I would like to coat the edge of this slab with some standard concrete or stucco to smooth it out and create a firm finish. Right now it is easy to take a finger to the vcrete and crumble it away at will. I don't like that. Also, there is an ugly joint where my cement board meets the slab. What's the best way to get this done? Which is better to coat the side of these slabs, stucco or some other product?

Can stucco be used to coat the cement board underside of the slab as well?