42" build in McPherson KS

[slschoming]

I am hoping to cap my dome this weekend and get started on my outer arch / chimney. Can I insulate and start my curing fires 1 week after capping the dome, or should I wait until 1 week after finishing the chimey? I will be using a clay flue liner on top of a firebrick arch and will be using homebrew to hold it all in place, but with the thermal break I don't know if the vent / chimney needs to be in place during curing as it will not be reaching the same temperatures as the dome. And advice?

[Gulf]

I think that 1" of each would be fine as long as you take the time to fit the ceramic fiber blanket uniformly. I made a lumpy mess of mine. But, the Forno Bravo youtube channel has a great video on doing it right for a finished igloo shape. How to Insulate, Shape and Lath your Oven Dome

[slschoming]

Several have used chicken wire, mesh, and diamond lath directly over the ceramic fiber insulation. I'm not sure just how "reinforced" that is. To be a true reinforcment the wire needs to be embedded in the concrete/stucco layer. Otherwise you are just hanging the stucco on to the wire. I used spacers to hold the mesh away from the vermicrete. The vermicrete made a sold backing which allowed me to forcefully push the first layer of stucco into the void behind the mesh. This could probably done right over the blanket. But, it would compress the blanket a little imo.

I just measured and in 2 places I have 6 inches to the edge of my hearth/slab which is about a half inch from the fence... 3 of 6 inches will go to my ceramic fiber blanket. I could probably get away with two inches of a stucco/concrete layer and use thinner brick veneer in those 2 places so I'm not touching the fence or hanging over the hearth. Or I could do 1 inch vermicrete and 1 inch concrete/stucco... which is better?

[Gulf]

Several have used chicken wire, mesh, and diamond lath directly over the ceramic fiber insulation. I'm not sure just how "reinforced" that is. To be a true reinforcment the wire needs to be embedded in the concrete/stucco layer. Otherwise you are just hanging the stucco on to the wire. I used spacers to hold the mesh away from the vermicrete. The vermicrete made a sold backing which allowed me to forcefully push the first layer of stucco into the void behind the mesh. This could probably be done right over the blanket. But, it would compress the blanket a little imo.

[slschoming]

I had ceramic fiber blanket for the insulation layer. 3" to 4" of vermicrete to true things up and act as a backer for a stucco layer. . It started out as that but, after adding a mesh reinforcement and special additives, it became more like ferocrete than actueal stucco. It is from 3/4" to 1" thick.

I got enough ceramic fiber blanket to do three inches of that, but beyond that my space is pretty limited. What do you think the bare minimum would be that I could get away with? Could I skip the vermicrete layer and do 3/4 to 1 inch of mesh reinforced stucco right on the ceramic blanket?

[Gulf]

Gulf what material / how thick of a layer did you put between insulation and exterior brick veneer?

I had ceramic fiber blanket for the insulation layer. 3" to 4" of vermicrete to true things up and act as a backer for a stucco layer. . It started out as that but, after adding a mesh reinforcement and special additives, it became more like ferocrete than actueal stucco. It is from 3/4" to 1" thick.

[slschoming]

The sketch shows adequate buttressing. For the dome, it looks like you want to brick the outside. I suggest you look at how Gulf did his, He sliced his brick side make about 1" veneers. Looks really nice.

Yeah, I am planning to slice the old bricks that I have been collecting down to 1-2 inches thick (varying slightly for an intentional uneven look). I am going for a "been here for 100 years" look and will be using a mix of reds, yellows, and darker bricks (similar to cobblerdave ) if I can find enough of each color.

Gulf what material / how thick of a layer did you put between insulation and exterior brick veneer?

[UtahBeehiver]

The sketch shows adequate buttressing. For the dome, it looks like you want to brick the outside. I suggest you look at how Gulf did his, He sliced his brick side make about 1" veneers. Looks really nice.

[slschoming]

I made more progress on the dome yesterday. I started using thirds instead of halves on course 9. There is some ugly stuff that I am not proud of going on where the dome meets the top of the arch, but it is solid and no one will ever see it.

I have 3 courses left + keystone so I need to get serious about what I'm doing for the chimney.

cobblerdave Here's a rough sketch of how I am picturing my finished product (subject to change). I will do a double wall below my arch like yours, but then get more narrow on the way up the chimney. I think I'll use clay flue liners so I can use old brick commons instead of firebrick. The chimney will probably extend about 2 feet above the dome.



UtahBeehiver My neighbor stopped by while I was working and said "It looks like you're almost done with your beehive" and I thought of you.

[cobblerdave]

Gday
Its a while since I built my oven wow that long. Having a oblong dome opening sorta lends itself to a wide chimney. It’s also short, the domes the same height. It doesn’t have to draw as the smoke goes straight up from the entrance and out. The winds here come from the direction faced by the oven entrance but we do get the occasional strong westerly in august. The wind from behind the oven will get forced down the chimney and blows the smoke in your face. Pretty rare though.
The rear of the chimney is firebrick but the rest is brick commons, thats solid clay not house brick the ones with the holes.
Id buttress so it’s double brick ....lots stronger
enjoy the journey
Dave

[UtahBeehiver]

Load Diagram

[UtahBeehiver]

With a full hemispherical arch, think a half moon shape, the downward load of the arch is pretty vertical. With a half arch like yours the load moves horizontally, think of Notre Dame church walls with domes sitting on vertical walls. They have buttress supports to offset the horizontal load of the dome at the vertical wall joint. You can probably get away with is small brick chimney like Cobblestone Dave (notice on Dave's build his does buttress his outer arch. but not a full height, full chimney like Gulf's.

[slschoming]

UtahBeehiver Thanks, that's exactly what I needed to hear.. I will plan on building with firebricks.

I have read many comments on here that refer to buttressing and I have looked it up but I'm not sure I fully understand.. If I build straight vent walls and match the arch of my inner arch (adding enough width/height to allow for a reveal) all with firebrick and build walls outside of the firebrick walls using regular house bricks would that be sufficient buttressing? This is my first masonry project and I am trying to learn as much as I can as I go.

I am also not opposed to putting a duravent on top of a simple arch with minimal weight on top if necessary, just thought I could save a little cash by doing a brick chimney.

I like the look of a shorter brick chimney, but I also want it to work properly. What is the minimum recommended chimney height?

[UtahBeehiver]

I would not recommend regular bricks on the vent area or interior of the chimney, too hot. A chimney vent on a fireplace will have a clay liner. Speaking of chimney vents, the existing shape of the arch does not lend itself to a heavy chimney load without buttressing the side walls. So if you build a brick chimney of any height you will need to buttress the side walls.

[slschoming]

I like the idea of the L shaped vent arch. I assume if I go that route I'll need to fill in this gap (circled in red) with a little wedge so my inner arch is a consistent distance from the vent arch all the way around?

Also, can the vent arch and chimney be built with regular brick? I plan to finish the outside of my dome similar to cobblerdave's oven and I have been accumulating old house bricks for this purpose. It might be nice to do the vent arch with house brick from the start so there is no extra layer required around it when I'm done. Does that make sense?