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Post by dilby on Apr 27, 2017 15:20:52 GMT
Hi all - I'm looking to create an outdoor oven and am after some tips. In short, it's not only Pizza I want to be cooking, and I've seen a few pizza ovens that I think are very shallow; designed to slide a pizza in but nor perhaps a roast chicken. I'm trying to at this stage work out the best design and then move onto how i'll actually do it - so reverse engineering I guess! The two main designs I see are the ones that are like half a sphere, and many people seem to use a yoga ball as a form for this. The second, and the one I'm meaning towards as it's more of a better shape and size for an oven, is what is essentially half a cylinder - so it has a flat back and arched sides. I've attached an image of one I saw on google images that seems quite simple. So some initial questions I'd be very grateful if someone could answer: - What are the differences between these two shapes in the way it actually performs? - How necessary is a door on the front? - In the example image there is simply one layer of bricks - is this generally thought to be enough to hold heat for long enough? Many thanks!
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Post by moonhead on Apr 30, 2017 8:42:49 GMT
Hi dilby and welcome Both styles of oven will give you any style of cooking, pizza, bread, roast, slow roasting...... For me it came down to how confident I felt with my none existent building skills - so I opted for the vault (half barrel). The Igloo style of oven is by far the most popular and efficient performer but no matter the style you choose, both will give fantastic results. As for doors, if you want to get more from your oven then yes you want a door. It will help the oven retain heat once the flame has gone allowing you to use the retained heat for another cook. The answer to your last question, in use these ovens heat upwards of 700 degrees F. An uninsulated oven as in the pic will cook pizza as long as there's a flame, but the outer brick face of the oven will be dangerously hot. So definitely insulate, under and over. It is essential to retaining the heat in the oven for other styles of cooking other than pizza. Best advice to give you is check out the builds on this forum. Under the General heading are sections for all styles Pompeii, Barrel and clay/cob. Read people's build threads this should help you decide which style of oven suits you best. Rick ukwoodfiredovenforum.proboards.com/thread/1112/barrel-vault-oven-build-durham
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Post by oblertone on May 3, 2017 8:14:14 GMT
- What are the differences between these two shapes in the way it actually performs?
Very little difference in performance if correctly built and insulated. Domes are naturally self supporting and easier to build 'free hand' while barrel vaults require forms to support the structure while building. Because of the way the forces act in a barrel vault they generally need exterior bracing to counteract expansion and contraction when in use, although they do offer better floor space for bulk cooking.
- How necessary is a door on the front?
A door on the front is largely decorative however if you wish to use your oven for retained heat cooking i.e. baking or roasting, then you need to separate the inner oven from the flue, this is normally achieved by building a lip into the structure, then placing a removeable inner door tight against the lip; this will kill the fire but prevent the oven from cooling too quickly.
- In the example image there is simply one layer of bricks - is this generally thought to be enough to hold heat for long enough?
The pictured design will eventually cook pizza, but nothing else. A single brick is usually 4" thick, heat travels at roughly 1" per hour, so after 4hrs the exterior will be as hot as the interior and radiating heat; this is not only wasteful but very dangerous to users and spectators. That being said, a single brick dome/barrel will work perfectly well if is is properly insulated to the extent that the exterior is safe to touch even when the interior is at 550c. Many builds exceed this standard and will be at little more than ambient temperature on the outer surface during use.
My build is one brick thick, will do pizza all night; slap in the removeable (insulated) door and without further firing will do breakfast and bread in the morning and a roast in the afternoon. Some of the builds on here will retain useful heat after three days, the key is insulation.
One further point for clarity; the oven in the picture has a flue within the main oven, this design will allow precious heat to escape before it has warmed the structure. In a 'classic' build the internal height of the oven (dome or barrel) and the height of the entry arch to the oven have a strict relationship (63% is optimal); this will trap heated gases within the oven which allows the heat to soak into the structure before the gases exit into the entry arch and up the flue. As they exit they will create a draw of fresh air into the oven.
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Post by dilby on May 5, 2017 8:29:34 GMT
Thanks so much for the replies everyone. Because of space limitations I'm leaning towards building a base and then getting some bendable ply bent in an arc shape with two lengths of timber branding it - this will give me an arch I can build my bricks over. I'd then insulate with insulation and chicken wire before covering in cement. I'd do this for the insulation but it will be quite near a wooden fence so I don't want the outer to be too hot. What I don't fully understand is an inner and outer flu - oblertone, do you have a picture of this or link that I can see as a reference? As far as I can tell, all the builds I've seen have a flue which just comes from the main part of the oven. Can I use a flue with a stop on the top or adjustable vent instead? Also, oblertone you mention an barrel vaults being liable to cracking - is there a particular cement that can be used to help with this? Also, I cannot find an example of how such supports would work - are they just internal vertical struts or more like wall ties? One more question, is do I really need fire bricks? Perhaps I sound stupid, but as far as I'm aware standard bricks are already fired at very high temperatures, so why can I not use them in an oven? And do I need to use firebricks just for the base that food and coals will sit on or the entire build? Thanks so much!
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Post by oblertone on May 5, 2017 9:06:58 GMT
Not sure where 'inner and out flue' comes from but try looking through my build thread (below) for an example of the inner oven being used without any flue, then a flue being added in the entry arch. You can use a flue stop or adjustable vent, but as you'll still need a door, why not just create a lip and stand the door against it ? The best cement mix for a WFO, whatever the shape is called homebrew; it is a mix of sand/cement/clay/lime in the ratio of 3-1-1-1 by volume. It is cheaper than any ready mix, easy to work and most suitable for the temperatures your oven will reach, typically 550c. The bracing commonly found on barrel ovens is extra buttressing at the base to prevent the vault walls pushing out. Metal supports have been used but differential expansion can cause stresses. No you don't need fire bricks, any solid building brick will suffice, old wire-cut solids can be found but are increasingly rare. A reclamation yard my do you a deal on damaged or half bricks with which you could build a dome. Avoid any bricks with holes all the way through, indented ones are fine. I got mine out of a neighbours skip after a 200 yr old chimney was demolished. Floor bricks could be fire brick, but heater blocks from old storage heaters are much cheaper and work well.
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Post by dilby on May 5, 2017 15:50:45 GMT
Thanks Oblertone, so much useful information - apologies for the continuos questions, but....
Can a concrete paving slab be used as the base?
Also, you mention in your first post that single skin brick is dangerous, but then go on to say that's what you have. Do you have any further insulation on the outside, and if not, how do you find using it given it's dangerous?
Also I'm still lost about this lip business - you say there is a post below but did you forget to post a link?
My best guess is that you mean you build a little internal shelf in that sits below the opening of the flu. Perhaps this stops hot air going straight up and out as hot air rises, but does help air circulate and eventually escape. Is that a good guess?
Many thanks again! Invaluable support.
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Post by dilby on May 6, 2017 8:28:58 GMT
Also one more question; does the pizza oven need to be vaulted? I was thinking last night it would be so much easier to simply build a box! But would this stop the air circulating in the right way? (I figured that our ovens are boxes!)
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Post by oblertone on May 6, 2017 10:01:24 GMT
On the bottom of my post(s) there is a link to my build thread, albeit hosted in another very informative site. This details my build in pictures which may assist. Yes I have a single brick dome, but it is insulated, rendered and then tiled. Mine isn't as fully insulated as I'd like but I ran out of room on my mobile build.
Slabs can be used as a base, but there needs to be some insulation between them and the oven floor otherwise you'll spend time and fuel heating them up. Wherever base structure you use should be topped by insulation before you lay the oven floor/cooking surface; I used vermiculite board, but there are plenty of alternatives.
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