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

[Gulf]

Xizenta,

All The ITs that I have seen so far have some off set. You will want to trim some of that 2X4 away on the leading edge to keep it from dislodging a freshly placed brick. If I understand correctly your inner arch will be made totaly out of 1/2 brick. If so, the upper brick of the arch will not reach far enough into the dome. It will work just fine but, you will have to compensate with a make up row to get back to round above the inner arch. Take a look at jonv 's inner arch. It shows how the inner arch transitions from about a half brick at the base to nearly a whole brick top dead center. When you tie the inner arch in with the dome it will be buttressed. However, the outer arch is a different story.

[xizenta]

Here are some progress pictures guys.
I ended up buying a harbor freight tile saw.

Since I had the ability to slice bricks more easily I went with a little more secure design and did a half-soldier for the first course rather than a full soldier.

We used a large caster wheel for the IT. I am a little concerned about the size of the wheel making this tool essentially a two-point-pivot. When you are measuring out at an angle where the wheel and base are in line with the target, I am sure it will extend slightly farther, as opposed to when the tool is completely horizontal or completely vertical. Should be OK but in hindsight a smaller wheel would have created a more true sphere.

Very very confused about how I want to do my vent. I am creating two sets of archs, one behind the other. The back arch will sit about a half inch lower than the opening arch, so that we have a 1/2 inch reveal for a door jam. That back arch will be made out of half bricks and be about 4.5 inches deep. The front arch is a full brick arch, about 9 inches deep.

My plan for now is to use half bricks for the three middle pieces of the front arch, leaving a rectangular (trapezoidal prism) opening which spans about three bricks wide and 4.5 inches deep for the vent. The question now is how to transition this into a 6 inch pipe.


Also, the left wall on my entry arch is kind of leaning. I am thinking about whether I will want to buttress it. Though it may not be necessary anymore now that I am using a stainless pipe chimney instead of a brick one.

[deejayoh]

Good call. You are goint to be putting about a ton of weight on the board. No need to fasten it down. It'll stay there.

On your slab - I would cut away the cement board around the edge to clean up the look. Then perhaps think about using tile on the edge for appearance.

[xizenta]

Anyone with feedback regarding the stand we have so far is welcome.

Also I purchased the ceramic fiber board today which will go under the oven dome. Are these typically cemented in place to the slab, or held down to the slab using any other method? Or are they free-standing on the slab?

[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?

[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)

[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.

[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]

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.

[deejayoh]

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

[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.

[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.

[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.

[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.

[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.