Honey, I shrunk the pompeii! 26 build

[pepe]

Hey Guys!

I hope you all are doing great. I am starting my new oven, I moved about a year ago and had to part ways with my 36" oven. I had a few months of withdrawal, and I just couldn’t live without it, my family needs another one... so without further ado, I am building a new one.

The thing is, I am limited space wise, the wife asked to not go beyond the available dimensions... 25" deep x 35" wide. I know. STOP IT I KNOW

But I am very excited I think I might just make it work.

I would really appreciate feedback.

The idea: I have two layouts, #1 respects wifes wishes and builds a 22 inch oven, I dont know if this is too small, we only make pizzas and some cuts of beef or chicken. The other option (I prefer this one) I modify my table layout and add maybe 5 more inches of workspace to build a 26 inch that I think will be very nice to use.

Plan:

1. 6 centimeter deep oven walls (that is how tall my local firebricks are).
2. Firebricks will be broken into thirds, maybe even further halved, to be used as Rubble Masonry style (lots of homebrew mix will be used).
3. A Styrofoam / expanded polystyrene / unicell 65 cm (diameter) half sphere will be used as form.
4. I will build up to the oven entrance, there will be no landing, this gives me about 27 inches deep construction oven.
5. 2 inches of oven insulation bellow and on dome calsil board / oven blanket.
6. 4 inch ss thin exhaust pipe (next measurement is 8 inch, itīs too large, hope 4 will do)
7. Thin Stucco Finish.


Questions / doubts:

1. Should I abort and make a squarish build? I really enjoy looking inside and seeing a beautiful dome.
2. Door will be 16 inches w x 9h inches, the 63% rule is not respected, so should I build it taller, take it up 1.5 inches and make about 14.5 inch height?
3. Is 16 inches too wide?


Construction is definitley not my strongsuit so really, any feedback is reaaaally welcomed!

Thanks,
Jose.

[david s]

I see a problem in cutting the firebricks into thirds and using them as brick units. Folk who have tried using firebrick splits (2" thick have found laying them on edge creates an insufficient bond between the brick units and their ovens tend to want to fall to bits. One of the reasons brick units are 4" wide is to have a sufficient surface bond and that's why laying bricks on edge for a wall is considered inadequate. You could make the walls thinner by casting the dome (most casts go for a 2" thick wall thickness. The aggregate for any castable mix "should be made up of particles of various sizes, from about 1/4" in diameter 1/4" in diameter to grains small as sand or smaller. The proportion of very fine particles should not be too great however." (Daniel Rhodes: Kilns)
The ovens I build are only 21" in diameter and perfectly adequate for a small family. The few time I wish the oven were larger are well outweighed by the number of times I take pleasure in its fuel efficiency and performance.
A 4" diameter flue pipe is inadequate for any oven IMO. You'll smoke out that room with a 4" pipe. (mine sport a 5" pipe). Your local metalwork shop will easily be able to make you one in 304 stainless.

[pepe]

I see a problem in cutting the firebricks into thirds and using them as brick units. Folk who have tried using firebrick splits (2" thick have found laying them on edge creates an insufficient bond between the brick units and their ovens tend to want to fall to bits. One of the reasons brick units are 4" wide is to have a sufficient surface bond and that's why laying bricks on edge for a wall is considered inadequate. You could make the walls thinner by casting the dome (most casts go for a 2" thick wall thickness. The aggregate for any castable mix "should be made up of particles of various sizes, from about 1/4" in diameter 1/4" in diameter to grains small as sand or smaller. The proportion of very fine particles should not be too great however." (Daniel Rhodes: Kilns)
The ovens I build are only 21" in diameter and perfectly adequate for a small family. The few time I wish the oven were larger are well outweighed by the number of times I take pleasure in its fuel efficiency and performance.
A 4" diameter flue pipe is inadequate for any oven IMO. You'll smoke out that room with a 4" pipe. (mine sport a 5" pipe). Your local metalwork shop will easily be able to make you one in 304 stainless.

Thank you very much for the reply.

I really hoped the 1/3 bricks build would work, I thought it was practically the same as a full pour on cast. Since I am 99.99% sure my ability to cast the oven is very bad, I will change the layout, will use half bricks, this gives me now a 11 cm / 4 inch aprox wall dome. Resulting in an interior of 21.5 inches, not bad at all.

UNLESS

David, this might sound confusing, but, the closest way i think I could manage into casting a dome and give it the look I am aiming for, would be to sort of break the firebricks into small rubble chunks like you quoted, and throw the smalles ones into the homebrew mix and kind of little by little splat them / buttress onto the unicel form. But before applying the mix on the unicell, place wet, larger but thinner pieces of firebrick first on the unicell. This would reveal a "fake" random rubble rock face inside the oven dome face that I hope should not comprimise dome stability.

If adding the rubble face is a no go but buttressing/splatting method to cast is workable, I could just make the homebrew and add the 1/4" broken firebrick pieces. I know you gave me your opinion, but do you think this would suffice? It would help maintain a bigger cooking area, about 25.6 inch surface.

I am already looking for a 5 inch pipe.

THANKS!

[david s]

The only way to find out is to build it. From my own experience crushing dense firebrick with a hammer down to 1/4” is time consuming and very laborious. Even crushing insulating firebrick with a hammer is tough work. I was quoting from Daniel Rhodes and he is writing about kilns. As our ovens only see around half the temperature of that of a kiln and correspondingly around half the thermal expansion, so you can get away with more although the same principles apply.
One of the beauties of small ovens is that they require far less materials and far less labour, so pushing the envelope is no big deal. Give it a shot.

[pepe]

The only way to find out is to build it. From my own experience crushing dense firebrick with a hammer down to 1/4” is time consuming and very laborious. Even crushing insulating firebrick with a hammer is tough work. I was quoting from Daniel Rhodes and he is writing about kilns. As our ovens only see around half the temperature of that of a kiln and correspondingly around half the thermal expansion, so you can get away with more although the same principles apply.
One of the beauties of small ovens is that they require far less materials and far less labour, so pushing the envelope is no big deal. Give it a shot.

David you should give pep talks for a living!

You are right, I am now starting the project. Last time I made the homebrew I used grey cement, my hometown has a lot of white cement, itīs the same stuff just white. I was wondering, have you cast one using white cement and fine silica sand? Thought it might look good.

[david s]

Funny you should be suggesting that because that’s exactly what I used to do for a living. I’m an ex visual arts teacher and a big part of the job was to encourage teenagers to dare to be creative.
I sometimes use white cement, but for me it’s double the price. We also have off white cement, a little cheaper, but also expensive and somewhere between white and grey in tone. I’ve not tried it in homebrew as I use castable refractory, but it is great if you want to add an oxide to colour the cement. You get much better intensity of colour.

[pepe]

That is so great to hear!

I canīt find anywhere on the forum, should I add something on the brick floor before y start casting over my unicel form? I am afraid it will dry and bond onto the brick floor and wonīt be able to expand thermally. Is there a simple solution?