Any advice?

[jackh]

Hello to all,
I am planning to soon begin construction of my first Pizza oven (allthough i have participated in a quick and rough construction in a oven building workshop) which I hope to make a interesting object (see my CAD images) but I am worried that the aesthetic aspect of my design might compromise its basic functionality! I'm hoping that anybody with some experience with wood fired ovens could help, any advice would be much appreciated!

The images are only rough and dimensions are yet to be finalized, I have a reasonable amount of building experience and I am confident that I can build it (it will be difficult but I have a plan) and that it will be structurally sound. However I worry that: Firstly, the angled flue (see section drawing) will hinder ideal air currents and that the oven might smoke through the door or the fire simply won't burn properly? And secondly that the design concept forces the interior dome (ie. the oven) to be located in the volume of the 'sphere' at a impractical distance, that is, the front of the oven cavity will be approximately 700-800mm in from the exterior surface ,i.e. beyond reach by arm, so that cooking and the cleaning of the inside will only be able to be done with tools attached to rods, extended to be able to reach the interior space... do you think this would be too impractical?

Any thoughts?

Cheers

Jack

[dmun]

It looks good. We actually had a member who built a spherical oven enclosure (unique oven enclosure): it was inside a channel marker buoy, and the steel shell formed the exterior of the enclosure. There's no problem with the angled chimney: a lot of Italian pizzaria ovens have the vent offset so it comes out the top of the dome. If you place your oven more to the rear of the enclosure you'll have more room for the entry/vent area.

My main concern is that if you build the outer enclosure of brick it may not be water resistant enough. You may have to do some sort of inner liner over the insulation, then have drip gaps in the brick below the oven floor. You'll also want some sort of drip ledge over your oven door.

A final thought is that the angled section of the flue may not be sufficient to prevent smoke leak on startup, but a chimney extension on top may not be the look you're going after.

Good luck on your project. Keep us posted.

[Tman1]

What's preventing you from moving the actual oven forward lowering the distance in to it? That part sounds, bad is too strong a word... unenviable. =]

[nissanneill]

Hi Jack and welcome aboard,
Great to see yet another Aussie on deck ready to face an oven build.
Your project looks quite impressive and challenging to say the least but I feel achievable.
Put a few words about how you intend to construct it and as shown, I am sure that other members will chime in to offer advice on your thoughts/plans.

Good luck an keep the pics flowing.

Cheers.

Neill

PS where abouts in Australia are you located?

[Neil2]

"What's preventing you from moving the actual oven forward lowering the distance in to it?"

Or a smaller sphere on a short pedestal ?

[Alter ego]

That is a great looking idea and one worth stealing!

One way to make the oven easier to reach inside would be to keep the large outer ball and bring the oven further forward within it. There is no real need to have the oven in the center of the ball and you still should have room for the smoke vent over the top of the oven. The larger area at the back of the oven could just be fill or more insulation.

Go for it! It would look very striking in the right setting.

[jackh]

Hi everyone,
Thanks for all of your feedback; you’ve given me a little more confidence to move forward with the project… The wheels are in motion, I’m hoping to finalize the design in the coming weeks and I’ve been collecting scores of red bricks that were being thrown out in a number construction sites around the place and have just sourced a large number of beautiful old hand made bricks up in the country, I should soon have all the bricks needed for the project and will be ready to begin!..... anyway, I’ll try to respond to all of you individually…

Dmon: when you say that you worry about the water resistance of the outer brick enclosure, is this because your thinking that the insulation may become saturated and not perform correctly? I was thinking that I would, after constructing the interior dome and covering it in insulation, I would put a thin layer of concrete reinforced with chicken wire which the outer brickwork would subsequently be laid on (see my section drawing), perhaps if you think that this is insufficient I could cover the concrete in water proofing membrane first, or just use a water-proofing agent in the mortar mix that brickwork will sit on?... Not sure what you mean by “drip gaps in the brick below the oven floor” could you elaborate?... I’m not too keen on the idea of building the chimney up, but if it turns out that it doesn’t draw the smoke properly I could always build it up after..

Tman and Alter Ego: See my revised drawing, I have moved the interior dome forwards as much as I think is possible and this means that the beginning of the oven dome will now be 500mm in from the front which is better but probably still not ideal. It’s a bit a balancing act, as moving the dome forward reduces the space between the outer spherical form and the interior dome so that the chimney is restricted in its dimensions, its angle and whereabouts the smoke shelf and chamber can be placed (on that note, do you or anybody else know how important it is to include a smoke shelf and chamber? Does the arrangement in my drawing seem alright?). Furthermore I worry that having the chimney pressed up so close to the interior dome won’t allow sufficient insulation of the ovens thermal mass, but I was thinking that if part of the chimney was lined in ‘insulation tiles’ (not to sure what the actual material is called but it’s the stuff used to insulate the inside of potter’s kilns…) might do the trick?

Neill: I’m a Melbourne man but the oven is gonna be built out in the bush at a family property in Central Victoria… my construction plan is roughly this (also see the attached PDF)…

Stage 1: excavate and pour the footings reinforced with heavy steel reinforcing bars bent in the centre and left sticking upwards such that they can later be bent into position and tied into the concrete mass of the ‘bottom hemisphere’

Stage 2: mound up a heap of earth and carve out the negative form of the bottom hemisphere by revolving a semicircular plywood cut-out (for accuracy, perhaps the plywood will be hung from a temporary structure above, if that makes any sense?)

Stage 3: lay the bricks around the inside of the mould trying to maintain consistent mortar joint dimensions and horizontal courses (which means a huge amount of brick cutting). Between mortar joints strips of chicken wire or brick ties or anything of that sort will be placed so that they extend inwards so as to tie the brickwork in to the subsequent concrete mass so that they won’t fall off under gravity after removal of the mould (hopefully!)

Stage 4: After the brickwork of the bottom hemisphere has been finished, bend the reinforcing that extends out from the footings appropriately (so that there is no possibility of the final product rolling down the hill!) tying in additional reinforcing mesh. Fill the hemisphere with concrete, rocks, broken bricks and anything to take up the space … once the concrete has cured the earth mould can then be removed…

Stage 5: put a layer of insulating material (not to sure what to use yet although I have read, if my memory is correct, that ‘vermiculite’, is the stuff to use) above the concrete surface and lay two layers of terracotta tile bonded with fire clay to form the oven floor.

Stage 6: mound up earth and carve the dome form of the interior oven space using a plywood cut-out and build up a single skin of halve bricks with a mix of standard mortar and fireclay.

Stage 7: build the angled chimney somehow… I haven’t yet clearly visualized how it will be done (probably the kind of thing I’ll just have to work out in the process of construction), but I think it should be manageable using some sort of temporary formwork to support a concrete and/or brickwork structure

Stage 8: Cover the dome with a heap of insulation (again not yet to sure what kind of material to use?) and cover it in a heap of clay to build out the form close to the circumference of the exterior brickwork. Slap on a small concrete shell, reinforced with chicken wire over the clay, again, molded with a ply cut-out, to give a solid (and waterproof?) surface in which the final brickwork can be laid.

Stage 9: build the final exterior layer of brick coursework using a ply cut-out hung from above to ensure an accurate form.

Finished!

Neil2: Your idea of a smaller sphere on a short pedestal has its appeal in that it would be a lot less work and a lot less wasteful (given the huge amount of dead mass which my current design depends on) however I have an irrational tendency (which I’m generally comfortable with) to commit to doing things the hard way for some arbitrary aesthetic end even though I know that I almost certainly will come to regret it half way through the project … Thanks for the suggestion though

I also have a few additional questions to ask if I may. I’m wondering if somebody could advise me on what would be the ideal dimensions for the opening into the oven and the ideal dimensions of a cross-section of the chimney?

Cheers,

Jack

[Lburou]

Your talent is obviously thinking outside the box.

Subscribing to this build to watch your dreams grow.

I'm sure you'll want to insure the ultimate performance of your oven. One thing in your design that strikes my concern is how you plan adequate insulation between the dome mass and chimney flue (given such a confined space). Without adequate insulation, the heat will migrate from the dome directly to the flue and decrease and otherwise interfere with the heat holding capabilies of your oven.

If you bake only pizza, that is not a big deal. If you want to bake bread and such, the impact would be greater.

You have a fabulous imagination and obvious creativity....Good luck and enjoy the process

[nissanneill]

Jack,
I just updated my Aussie list. You are now on the Melbourne list.
Just reading your plan of attack, one hell of a lot of bricks and cutting amongst other potential nightmares.
I see a problem getting your mortar joints in the lower hemispherical sphere accurate and even especially when hidden in the earth pattern. Maybe cut a heap of high density plastic strips 10mm wide and use them as spacers which after you remove the mound, pull them out and point the joint to suite your likes.
I have also been thinking of pre-casting 2 reinforced concrete semi spheres, one for the top and the other for the bottom of your build. You might even be able to include some reinforcing/retaining galv wires around the proposed mortar joints for the rows of bricks and cut/lay the bricks and then using a crane/loader/forklift place them into position. This would make the tasks of even brickwork and better shape much easier but sets up another challenge in positioning.
The bottom one would be easy once you overturned it, leaving a large circular hole left to allow your reinforcing steel to protrude, easy to pour your concrete and rubble fill.
The top one could locate over a raised locating concrete rim which can be done with your inner fill, but this would go on after your hearth, oven dome with insulation, and chimney. Putting just the precast semi sphere on would then be easy as your opening would be cut out and then brick your outer bricks.
Again, thinking outside the sphere highlights options which might make the task easier/quicker/better.
Good luck.

Neill

[dmun]

Dmon: when you say that you worry about the water resistance of the outer brick enclosure, is this because your thinking that the insulation may become saturated and not perform correctly? I was thinking that I would, after constructing the interior dome and covering it in insulation, I would put a thin layer of concrete reinforced with chicken wire which the outer brickwork would subsequently be laid on (see my section drawing), perhaps if you think that this is insufficient I could cover the concrete in water proofing membrane first, or just use a water-proofing agent in the mortar mix that brickwork will sit on?... Not sure what you mean by “drip gaps in the brick below the oven floor” could you elaborate?... I’m not too keen on the idea of building the chimney up, but if it turns out that it doesn’t draw the smoke properly I could always build it up after..

My only concern is that your brick sphere is going to soak up water like a sponge when it rains. If you make an inner waterproof layer, separated by a gap from your outer brick layer, and give some way for any moisture that accumulates a way to get out, then your oven may have a better chance of success. If you look around your neighborhood you won't see many homes with brick roofs. The porous brick structures are always capped with some sort of stone, shingle, or flashing to deflect moisture away from the brick structure. In those rare instances where bricks are exposed horizontally, like front steps, it's not unusual to see them crumble away in a few years from freeze/thaw cycles. Also, in that particular instance, the steps are usually filled with some kind of rubble which it's not important to keep dry.

I'm not proposing a solution, just suggesting you give the water issue some thought.