pumice oven build

[jacobyu]

Hey All,
I am looking to build a new oven and have a few questions about this build I found on youtube. I am attracted to the design/build due to its portability and relatively light weight - I currently rent, and would like the ability to move the oven with two people. https://www.youtube.com/watch?v=Sny2MCND3nA The material used is pumice stone:

1. is pumice considered a refractory material? is it an appropriate material to use for a pizza oven like this?
2. what are the disadvantages of this build? obviously, it is thinner than most designs I see here and does not have a lot of thermal mass. There is another video of the oven in action and the temperature is at 850 - is this sufficient temp for good pizza cooking? It won?t have as much heat retention properties for baking, but I am more concerned with the pizza cooking/faster cooking.
3. how would you improve on this build while keeping the compact design/portability?
4. the guy in the video grinds his own pumice, but I have found a distributor fairly close to me - http://www.hesspumice.com/pumice-pag...des-types.html Which grade is appropriate? I spoke with them on the phone and it seems very cheap - $90 for 2500b and they are ok with selling me a smaller quantity.
5. the floor: the guy used a finer pumice grind for the floor but adds a tile on top of it for cooking. i?d like to have the floor be whatever surface I want to cook on - what would you do? I am thinking embedding a pizza stone could be cool, and would stay lightweight.
6. if everything else checks out, what would you advise as a dry time? The guy recommends two month dry time before first fire - is it necessary to go that long?
7. I live in a fairly cold climate - can get down to 20 below - is the oven ok being left outside? thanks!

[cobblerdave]

G'day
Yes I've seen a few of this ovens mentioned from time to time. Seem to remember a few New Zealanders have made this type. I suppose that pumice is pretty common in the "shaky isles" From the accent of the builder on your clip it appears he's an Aussie though.
As for how they work over the long term I couldn't tell you how they would go. If you did build one it be good to hear how it work over time.
As for it surviving outside in those types of temps I suppose anything that's not protected would suffer in the long term.
Regards dave

[wotavidone]

Hey All,
I am looking to build a new oven and have a few questions about this build I found on youtube. I am attracted to the design/build due to its portability and relatively light weight - I currently rent, and would like the ability to move the oven with two people. https://www.youtube.com/watch?v=Sny2MCND3nA The material used is pumice stone:

1. is pumice considered a refractory material? is it an appropriate material to use for a pizza oven like this?
2. what are the disadvantages of this build? obviously, it is thinner than most designs I see here and does not have a lot of thermal mass. There is another video of the oven in action and the temperature is at 850 - is this sufficient temp for good pizza cooking? It won’t have as much heat retention properties for baking, but I am more concerned with the pizza cooking/faster cooking.
3. how would you improve on this build while keeping the compact design/portability?
4. the guy in the video grinds his own pumice, but I have found a distributor fairly close to me - http://www.hesspumice.com/pumice-pag...des-types.html Which grade is appropriate? I spoke with them on the phone and it seems very cheap - $90 for 2500b and they are ok with selling me a smaller quantity.
5. the floor: the guy used a finer pumice grind for the floor but adds a tile on top of it for cooking. i’d like to have the floor be whatever surface I want to cook on - what would you do? I am thinking embedding a pizza stone could be cool, and would stay lightweight.
6. if everything else checks out, what would you advise as a dry time? The guy recommends two month dry time before first fire - is it necessary to go that long?
7. I live in a fairly cold climate - can get down to 20 below - is the oven ok being left outside? thanks!

Pumice is an extremely porous stone. It's essentially a foamed volcanic rock.
It's so light you hear about it floating on water. As a high temperature insulator it would be brilliant. As a wood fired oven dome, it's got very little thermal mass. It is the natural material that you would use over the top of an oven dome to stop the dome cooling too quickly. It is not the right material to make a dome or floor from.

[MeLoN BaLLaR]

Pumice is an extremely porous stone. It's essentially a foamed volcanic rock.
It's so light you hear about it floating on water. As a high temperature insulator it would be brilliant. As a wood fired oven dome, it's got very little thermal mass. It is the natural material that you would use over the top of an oven dome to stop the dome cooling too quickly. It is not the right material to make a dome or floor from.

I've been thinking a lot about this. I think a pumice concrete won't make a very good bread style oven. But a ~2 hour burn pizza oven?

2" dome of 4 pumice and 1 alumina concrete. pumice is 50/50 fines and 3/16's. Line the inside with 1" of: 1 sand, 1 alumina cement, 2 pumice fines, maybe an 1.5-2" on the ceiling. polish it if you are really into refraction. bottom is 2" of ceramic board, split firebrick.
Cover with 2" of ceramic insulation, chicken wire, 1 alumina and 4 pumice fines aggregate.

Will it stay hot for 12-24 hours for a bread bake? dunno. will it get hot enough and stay hot enough for a pizza party? I think absolutely. will it be light enough for 3 guys to lug around? probably.

yeah I'm new, not so bright, probably nuts. feel free to fire away...

[Tscarborough]

It is an insulator, not a heat sink. It won't work.

[MeLoN BaLLaR]

It is an insulator, not a heat sink. It won't work.

It probably won't work as a bread baking oven. It actually does work as a pizza oven. Some guy built one on Youtube, with zero additional insulation and zero refractory cement or bricks, and cooked a serviceable pizza. I'm not claiming it was the best pizza I've ever seen out of a homemade pizza oven. But, it was edible. and he was carrying the thing around before finally placing it on a very weak looking wooden table. https://youtu.be/uOJq6g4at-0

My question is, can it be made better? The goal is a inexpensive lightweight pizza oven that operates on a 36" diameter cooking surface scale (as opposed to say an uuni). Hence my build parameters above

[MeLoN BaLLaR]

It is an insulator, not a heat sink. It won't work.

Let's try this another way. The goal of any Mediterranean/Middle Eastern (I make Turkish style pizza's as well) style oven that cooks 1 pizza is say radiating ~700f on the floor and ~900f on the ceiling. A pumice based oven will radiate heat faster from the same amount of wood than a huge heat sink based oven. It will theoretically burn less fuel, get hot faster, etc than a traditional mass-based oven. Once the fire is out, the heat will dissipate faster (no mass to hold the heat). So probably no baking. But as long as there is a current heat source, and you can control the temperature (same problem as with a mass based oven) to hit whatever your cooking goals are, it should work for a pizza that cooks in 2 minutes.

If, like me, you haven't got a location to put a multi-thousand pound base and oven, and don't have a need to bake, this is worth investigating.

Sounds like a great party oven. Light it, pizzas for an hour or 2, then done. Has to be better than my BBQ pizza setup.

I genuinely welcome comments and criticism. My brain does not always give my body good information. I'm prodding you folks for more dialogue, positive or negative.

[admin]

MeLoN,

Not sure if you are interested, but since you mention Mediterranean Middle Eastern / Turkish style pizzas. We had a recipe contest participant submit a recipe for Damascene pizza.

Would love for your to share your Turkish Pizza recipe with our community cookbook.

Damascene Pizza recipe
https://www.fornobravo.com/blog/reci...ascene-pizzas/

Forno Bravo
Tim

[david s]

One problem with using any lightweight aggregate like vermiculite, perlite, scoria or pumice to a castable mix is that it drastically reduces the strength of the resulting cast. (see attachment).
This means your casting will be subject to damage through bumps and abrasions. Getting the mix light enough and yet still strong enough will be your problem, particularly if your walls are only 2"
Regarding the pizza stone embedded in the cast floor, I think you will find that it will crack as soon as you get a decent fire on it. I was given a pizza stone several years ago and tried it in my first oven, thinking it would be easy to clear the coals and ash off it because it was raised above the floor proper. It cracked right down the middle after the first firing. The problem is not the actual temperature it reaches, but its relative thinness and the fact it is being heated at around 400C/hr. You could try a kiln shelf, i think it should perform better.

Is there any further evidence on how this oven works in actual operation. I think the flue design is hopelessly inadequate. There is no funnelling to the entry of the flue and the diameter which appears to be around 2 1/2" is woefully small. I would expect tons of smoke would escape out the front. Also the door is better designed so that it fits in a lot deeper. i.e. when in place the flue is outside the oven chamber.

Also the builder does not say what type of cement he used. Was it calcium silicate or calcium aluminate?

[MeLoN BaLLaR]

One problem with using any lightweight aggregate like vermiculite, perlite, scoria or pumice to a castable mix is that it drastically reduces the strength of the resulting cast. (see attachment). This means your casting will be subject to damage through bumps and abrasions. Getting the mix light enough and yet still strong enough will be your problem, particularly if your walls are only 2".

Agreed. The mix I'm using is 400psi. About 5x weaker than a traditional portland mix. There will be little additional weight added to the outside of my dome other than the ceramic fiber insulation, chicken wire, a light pumice fines mortar and 8" flue.

Regarding the pizza stone embedded in the cast floor, I think you will find that it will crack as soon as you get a decent fire on it. I was given a pizza stone several years ago and tried it in my first oven, thinking it would be easy to clear the coals and ash off it because it was raised above the floor proper. It cracked right down the middle after the first firing. The problem is not the actual temperature it reaches, but its relative thinness and the fact it is being heated at around 400C/hr. You could try a kiln shelf, i think it should perform better.

I am planning a typical floor: firebrick(splits to save weight) on sand on ceramic board, then on pumice concrete. Then on whatever (probably sitting on my granite BBQ island).

Is there any further evidence on how this oven works in actual operation. I think the flue design is hopelessly inadequate. There is no funnelling to the entry of the flue and the diameter which appears to be around 2 1/2" is woefully small. I would expect tons of smoke would escape out the front. Also the door is better designed so that it fits in a lot deeper. i.e. when in place the flue is outside the oven chamber.

None that I know of. The designer made a flue cap. I am ignoring his floor and flue and going with an 8" flue, with a large opening in the door arch. And a door inside the flue exit chamber, isolating the entrance. Like an FB Napoli

Also the builder does not say what type of cement he used. Was it calcium silicate or calcium aluminate?

He used Portland. I just bought 2 bags of FB's mortar. My dome will be pumice and FB mortar. I am going to line the inside of the dome with ~.5"-1" of FB mortar, pumice fines, and firebrick aggregate concrete. I am hoping for a better refractory with the high alumina mortar and firebrick vs. straight alumina mortar and pumice. Probably worth the weight penalty.

thank you so much for replying. I very much appreciate your input

[david s]

I'd suggest if you are trying to save weight, apply this mix to the mould first, then make up your lightweight mixture over the top as soon as the previous layer has hardened. This will get a more successful bond than trying to trowel a thin layer inside an already hardened casting.It will also give you a much more even finish.
I like your idea of using the crushed firebrick, but make sure you use dense firebrick, using insulating firebricks will give you much the result as the pumice. There"s a fair bit of work crushing dense firebricks, I've done a bit myself. You will probably need to richen the mix with some more pure calcium aluminate cement (one brand is called ciment fondue) to balance the added aggregate. I think FB high temp mortar is a bagged blend of crushed grog and calcium aluminate cement, but you should ask them what the blend is, it could be just lime and sand.If you don't add more cement then your brew will likely be too lean.

Regarding the flue, you don't say how big you are planning your oven but as a guide for internal diam of 42" oven, use an 8" flue, 36" use 6", 24" use 5"
never go smaller than 4 1/2" (mine is 21" with a 5" flue)

[MeLoN BaLLaR]

"I am going to line the inside of the dome with ~.5"-1" of FB mortar, pumice fines, and firebrick aggregate concrete."

I am presuming you mean 5:1 of this mix. How thick?

I meant 1/2 and inch on the sides and 1 inch under the dome ceiling. The mix planned is 1 FB mortar, 2-3 crushed firebrick and 1-2 pumice fines.

I'd suggest if you are trying to save weight, apply this mix to the mould first, then make up your lightweight mixture over the top as soon as the previous layer has hardened. This will be more successful than trying to trowel a thin layer inside an already hardened casting.

This is a brilliant suggestion. I was going to line it after I had casted the dome because I am also trying to lower the dome height (36" dome, 18" dome height). But I can lower the dome height by raising the floor (splits to full bricks).

Diameter:	Height:	Diameter Ratio
34	14.75	43.4%
Diameter:	Height:	Diameter Ratio
36	15.75	43.8%

I like your idea of using the crushed firebrick, but make sure you use dense firebrick, using insulating firebricks will give you much the result as the pumice. There"s a fair bit of work crushing dense firebricks, I've done a bit myself. You will probably need to richen the mix with some more pure calcium aluminate cement (one brand is called ciment fondue). I think FB high temp mortar is a bagged blend of crushed grog and calcium aluminate cement, but you should ask them what the blend is, it could be just lime and sand.

My building supply guys have the yellow/brown 6-8 lbs firebricks. low-medium duty. Should work a treat.

[SIZE=14pxRegarding the flue, you don't say how big you are planning your oven but as a guide for internal diam of 42" oven, use an 8" flue, 36" use 6", 24" use 5"
never go smaller than 4 1/2" (mine is 21" with a 5" flue)[/SIZE]

I was going to go with an 8" since I'm running a Neapolitan style flue and chimney. If I change my mind and do a Pompeii style, I will drop down to a 6"

Thanks and Regards,

MB

[admin]

Regarding the pizza stone embedded in the cast floor, I think you will find that it will crack as soon as you get a decent fire on it. I was given a pizza stone several years ago and tried it in my first oven, thinking it would be easy to clear the coals and ash off it because it was raised above the floor proper. It cracked right down the middle after the first firing. The problem is not the actual temperature it reaches, but its relative thinness and the fact it is being heated at around 400C/hr. You could try a kiln shelf, i think it should perform better.

Most pizza stones are not designed to withstand direct flame, so even though temperature ratings can exceed 1,000 for some stones, we agree with David that it probably isn't a good idea to deign the stone into the floor.

Forno Bravo
Tim