First build. What is best for a small area?

[danno104]

Hi everyone,

I am hoping I can find some advice for building a pizza oven.
I would like to build a wood fire pizza oven. It only needs to be able to cook one 12" pizza at a time (especially if they cook in under 5 minutes) as my wife and I are grazers.
Our yard is small. It will be built on a steel base with the dimensions of 850mm(33") wide and about 1000mm(39") deep (the depth does have some wiggle room) so the finished oven size can not be larger than this.
I was looking at a dome style as people say they cook better but they seem to be larger than the space available. Barrel style seem more likely to fit but people do not seem keen on these for pizzas.
So my quesitons are:
Is Dome or Barrel style better? Or is there not much of a difference?
If the design is too large, could I scale it down and still have it work well?

[UtahBeehiver]

Look at David S cast builds, they are small dome ovens, heat up fast. Domes ovens will give you the best performance and they can be small, especially cast ovens. David S is our resident cast expert.

[danno104]

Thanks UtahBeehiver, I have been reading a lot of his posts and comments today and feel a dome oven is plausible to work with my size constraints
I noticed in post #9 David mentioned that most casts are around 2" thick yet in other posts I see it is suggested that a blanket should go between the clay and vermiculite-cement layers. So my question is if the blanket is about 1" thick, how thick should the clay layer and the insulating vermiculite layer be?

Also for the shaping of the dome, I have seen some people use sand covered in plastic/newspaper. Would the whole mound need to be sand for strength? or could I fill the bulk inside with say foam boxes so less sand is required? I could then break the foam boxes up to remove through the door.

For the base, my initial thought was to make a concrete slab about 75mm thick (with reinforcement) then build on top of that and put 2" base of firebricks in after so if they get damaged I can remove them however I see many people use a vermiculite-concrete base. Would this be used instead of a standard concrete base or as well as?

To help me with my design, would the chimney be better off in the dome itself? Or would it be better in the arch? Based on a number of drawings I have seen, I am becoming confused if the door should be able to sit past the chimney to essentially stop airflow or not.

Sorry for all the questions. I'd rather get it as right as possible the first time

[david s]

Hi Danno,

Check out the cast ovens in the Other Ovens section. There are plenty of well documented builds there that should answer most of your questions.
I've attached a drawing plan of a 24" internal diameter oven that should give you a start. It is best to draw up one starting with the internal diameter then add the layers to give you the external dimensions. You will need extra for the flue gallery entry. You can see that a 24" ID oven results in a 37" external diameter. You could scale it down further, the ovens I build are 21" internal, weigh around 250Kg. Because of the mathematics of volume a small increase in diameter results in a large increase in volume, weight and cost.

The drawing also shows a stick cut to half the diameter (giving you a hemisphere). This is what you build the sand dome around so you end up with the appropriate height. Yes some polystyrene boxes to part fill the sand form works well.

A 3" reinforced concrete slab should be sufficient for this sized oven, but remember that the strength of a concrete slab is proportional to the square of its thickness. eg a 2'' slab is only 1/4 strength of a 4" one.

For a small oven like this you need a 5"diameter stainless flue pipe.

[danno104]

Thanks David for the drawing. I will continue reading the threads.

[SableSprings]

We also recommend putting weep holes (3-5) through the supporting slab. You can use 1/2" plastic pipe in your form or by drilling after the pour (if you drill, make sure you know where the rebar is ). Place porcelain tile squares upside down on the slab, arraigned so you don't cover the weep holes. If you use scrap mosaic squares, the mesh backing will keep the perl-vermicrete insulation from filling the gaps between tiles. You can also lay garden cloth over the tile layer before you apply the 5:1 insulating perl-vermicrete layer. David's drawing with this addition is an excellent visualization of the oven cross-section. Looking forward to your progress and applaud your planning ahead!

[david s]

In addition, weep holes through the supporting slab, outside the floor bricks, that communicate with the dome insulating blanket, can also assist in keeping moisture out of this layer.

[danno104]

Thanks Sable Springs. Are you suggesting the base be made of Concrete (with holes) then a layer of tiles so the tiles help channel the water to the holes and not pool under the vermi-crete layer?
David do you mean put a few holes in the slab directly under the two blanket layers where it meets the floor as in this diagram

[david s]

Yes. The build up of heat and any steam in the insulation layers over the dome will highest at the top and force any moisture down, assisted by gravity and out the holes in the supporting slab. Also some near the centre to allow moisture out, underneath thr underfloor insulation.

[danno104]

Thanks David. Thats great to know!
I will draw up a plan soon and post it to see if it checks all the boxes.

[danno104]

Hi David, Sable Springs, and Utah Beehiver,

Below are details about how I plan to build the oven. If this looks right/usable, I will then look in to beginning sourcing materials, etc. I think I have covered everything... I will then begin to calculate volumes of required materials.

Stand

Total Dimension:
Width: 955mm
Height: 880mm
Depth: 955mm

Height Breakdown:

• (grey) Wheels - 191mm high. Weight rated to 150kg/wheel (Approx 450KG among 4 wheels). Swivel with brakes.
• (Yellow) Steel - Welded together to make frame 955mm deep and wide, 589mm high. Use 50mm x 50mm square galvanized tube.
• (Blue - not visible due to the angle of the screenshot and size of image)Concrete slab base (cement sheet/blueboard) - 10mm thick to help support concrete pour over steel supports.
• (Red)Concrete slab (12 bags) - 90mm. Use 25mpa after 28 days (standard) or 55mpa after 28 days (high strength) with 5mm reo mesh. Has 3 holes under Ceramic blanket layer and 3 holes under hearth area. Should I add more holes?

Oven Base/Herth

(Black)Tile mesh layer (approx 3mm/1/8") - To assist with drainage through holes in Concrete base
(Dark green)Vermi-crete (100mm/4") - 5:1 Vermiculite: Cement* (Ratio by volume as per https://community.fornobravo.com/fil...1&d=1572731611)
(Purple)Fire Brick (50mm/2")



Dome

ID = 300mm (12")
(Purple) Layer 1 (50mm/2") - Home brew - 3:1:1:1 Sand: Cement*: Hydrated Lime: Fireclay with polyprop fibres. (Are you able to help confirm for me that this is a volume ratio? I believe it is but would prefer verification)
(Green) Layer 2 (25mm/1") - Ceramic blanket - 3 holes in base (one at the back, 1 each side of the door) to allow steam/pressure escape
(Blue) Layer 3 (25mm/1") - Ceramic blanket -
(not visible) Layer 4 - Chicken Wire - to hold ceramic blanket
(Pale Yellow) Layer 5 (32mm/1.5") - Vermi-crete - 10:1 Vermiculite: Cement* (Ratio by volume as per https://community.fornobravo.com/fil...1&d=1572731611)
(Red) Layer 6 (19mm/3/4") - Render

*Cement bag composition = Portland Cement > 92.5% | Silica < 1% | Other non hazardous ingredients = Remaining




Door

Door Opening to internal of dome will be layered the same as the rest of the dome.
Door opening: 200mm high, 400mm wide. (I have now realised 64% high is about 192mm so I will make the door this height based on the 64% rule. I am unsure if the width is suitable thought as I have seen many discussions about door widths.)
Flue area 250mm high, 450mm wide, 160mm deep. Flue area will have a front lip (25mm/1" lower than flue area) to help catch smoke to go through flue.