Soon to begin my first pizza oven!

[mooney21]

G'day from Australia
i have a few questions to ask before i get stuck into to much planning and buying materials.

After reading and looking up different builds on here, i am stuck trying to decide brick or cast dome.
Cast is probably cheaper where i live as the fire bricks are very expensive but is it as good in the long run?
What size is preferable for someone who will use the oven frequently (2-3 times a month) for mainly pizza and the occasional roast?


i have a lot more questions but these few will decide which direction i will take this build.

[mooney21]

I have decided to go with a cast dome, ive been doing a bit more research and plan to start in the next week or 2.

i am currently searching for designs to cast the dome and opening in one piece ( if this is preferred ).
im thinking of using the wet brickies sand and news paper for the dome and then building a timber frame pushing it into the sand to form the opening.
Castflo 25kg AC1350G Refractory Castable is what i plan on using ( should this be mixed with bricks plasticiser or will that weaken the mix?


the sizes im thinking are:
900mm diameter for the dome which will make the height 450mm
400-450mm wide opening and about 350mm high to the highest point of the arch way.

if these sizes need revising i would be happy to take any advice on board.


Also want to make this mobile, in the sense i can make the oven and move it later on and place on another slab, so i would need the base to be solid and able to move.
so any advice on this would also be greatly appreciated.

[UtahBeehiver]

I'm going to defer to DavidS on one piece vs multi piece casting. The opening height should be around 63-65% of the dome height for your oven size.
So it should be around 292 mm.

[david s]

I have decided to go with a cast dome, ive been doing a bit more research and plan to start in the next week or 2.

i am currently searching for designs to cast the dome and opening in one piece ( if this is preferred ).
im thinking of using the wet brickies sand and news paper for the dome and then building a timber frame pushing it into the sand to form the opening.
Castflo 25kg AC1350G Refractory Castable is what i plan on using ( should this be mixed with bricks plasticiser or will that weaken the mix?


the sizes im thinking are:
900mm diameter for the dome which will make the height 450mm
400-450mm wide opening and about 350mm high to the highest point of the arch way.

if these sizes need revising i would be happy to take any advice on board.


Also want to make this mobile, in the sense i can make the oven and move it later on and place on another slab, so i would need the base to be solid and able to move.
so any advice on this would also be greatly appreciated.

Casting the dome in one piece is a lot easier than muti pieces although I think it's better to cast the dome and oven mouth in one piece, then a second casting for the flue gallery that sits in front of it. all done in situ. Here is a link to a well documented build done with castable.
Do NOT add plasticiser to the mix. Its action with CAC is way more powerful than with Portland cement and will result in the material slumping, which you don't want. Because you are asking the mix to stand up vertically for the first 100 mm or so it's already difficult. I'd suggest you build the dome casting up around that height and wait for around 2-3 hrs for it to harden, then proceed to do the rest. It gets easier as you go higher because it leans in more.

Regarding making it mobile, your 900 mm diameter is a pretty big sucker and will be very heavy and hard to move. If you only want to cook occasional pizzas and roasts for the family 650 mm would suit you better. Remember that fuel consumption is proportional to volume, So a 650 diam is less than 1.5 X a 900, but a whopping 2.5 X in volume. What this means in practice is that you will be reluctant to fire the larger oven for just a few pizzas.

Here is a link to a well documented build using proprietary castable that should answer many of your questions.


#1

[mooney21]

Thanks guys i will check out that post.

As for the first 100mm or so , would it be easier to make an outer mould just high enough to to support the mix until the slope is flat enough to support?

ok so 650mm i am fine to do as i will save in costs aswell.
what size opening should i be looking at? going off the 63% as suggested by UtahBeehiver its only giving me about 200mm which will make for a difficult time.
Do the same principles apply for this smaller build?

[david s]

You could make an outer mould for the bottom 100 mm or so but it’s extra work. Get the consistency right and the stuff will stand up ok.

Regarding the 63% rule, you can crib a bit and it makes no noticeable difference. Even as much as 70% is ok. Provided the door is a large radius arc rather than a semi circle, a 200 mm high door is plenty. Because you are casting rather than brick building then this shape is easy to do. Mine is only 160mm high because my oven is 540mm diam (255 internal height) and I can easily fit 2 large chooks or a 5 kg Turkey.

[mooney21]

Done a few drawings of sizes and design, do these look in proportion with a diameter of a 650mm oven?(not 610mm like the photos says).

just a few other sizes i would like to clarify before i forget.
rebate size - does this just need to be 20mm or so? just enough to catch the door.
flu size - i was thinking something around 100m in diameter.
calcium silicate board - only available in 25mm thick sheets down here in Tassie unless i order from Melbourne.
is that sufficient if i made vermiculite layer below cooking floor thicker?

[UtahBeehiver]

IMHO, 20 mm is enough reveal for the door. With the adjustment for the reveal on the arch height, the opening ratio looks good, IE (240-20)/330=67% but like David said, there is wiggle room on this ratio. You would be better with two layers of 25mm CaSi under the floor rather than 1 layer only or add 50mm of pcrete under one layer of CaSi.

[mooney21]

ok ill go with 20mm rebate for the door opening.

how much castable do you use in your shell for a smaller build DavidS? if i allow an exrta bag on what you use should be enough. stuff im ordering comes in 25kg bags

[david s]

For a 650 mm dome with 50 mm wall thickness you will have 40 litres. Generally what you don’t use where the oven door mouth is you need around the same amount for the area around it. So you will need 3 25 kg bags. The stuff does tend to reduce in volume by around 20 % when mixed with water and you will need extra to do the flue gallery so you better get 5 bags.
For the flue size 100 mm way too smal. You might get away with 125 mm, but I’d be going for 150 mm (6”)