Hybrid, Alan Scott/cob low crown bread oven

[yaffle87]

Hi there,

I wonder if theres some help I can get here;

My build is about 64"x52" (outer) 45"x32" (inner)using reclaimed Storage heater bricks for the hearth, with a sand and clay rich soil sub-floor. I have just enough firebricks for a side-end arch with a chimney outside door to contain steam effectively. I plan to clad the outside of the oven with an insulation layer of clay rich soil/sand, vermiculite and an outer cob layer with lime finishing plaster with a good amount of space around the door. I have had trouble with high ceilings in pizza ovens and want to make a more dedicated bread oven with a lower crown that I can use for small scale market baking as well as pizzas etc for supper clubs.

I have built many cob and fire cement pompei style ovens but this is my first try using brick arches, which I have no experience with.
I need advice on whether its possible to make the crown of the oven as low as 12" with the width of the arch being 32", with standard firebrick - I could afford to get a few keystones or some tampered bricks for edges but trying to keep cost right down and use what I have. this is bearing in mind the weight of a 6-8 inch cob and insulation layer on top of that.

The other thing Im deciding is whether to get cal sil board or not, Ive layed foundations and built a breeze block plinth and am going to start on a wooden base and surround for the sub floor. I would prefer to just make a hefty 6-8 inch clay/sand sub floor with enough heat retention for 2-3 bakes - I have plenty free clay but just wondering if I need a fire board to stop any heat loss underneath perhaps?

I will upload some pics if neccessary - Im currently scavenging all the leftover breeze blocks from my neighbours skip which is great and has done the job with the plinth, as well as around a ton of good clay from my garden. hope to keep all costs well under 200 smackers, have a load of leftover fire bricks from kilnlinings from my previous builds too but may need to purchase a few more, probably Vitcas without minimum order??.

Any professional advice much appreciated!

cheers

[simon]

With regards to the shallow arch, this is possible. A shallow arch like I imagine you're after will create large side ways forces which you'll need to control. This can be achieved with a decent amount of buttressing or weight, which is not a great solution, or you make use of some steelwork.

The steel solution is often used, so you can find examples of it out there. It is simply making use of a couple of steel beams/RSJs, that are pulled together by tightened down threaded rod. As an image speaks a thousand words, here's an example for you...

www.stovemaster.com/html_en/pop/ristow/ristow_00.html

Simon.

[downunderdave]

Feb 29, 2016 21:16:00 GMT simon said:

With regards to the shallow arch, this is possible. A shallow arch like I imagine you're after will create large side ways forces which you'll need to control. This can be achieved with a decent amount of buttressing or weight, which is not a great solution, or you make use of some steelwork.

The steel solution is often used, so you can find examples of it out there. It is simply making use of a couple of steel beams/RSJs, that are pulled together by tightened down threaded rod. As an image speaks a thousand words, here's an example for you...

www.stovemaster.com/html_en/pop/ristow/ristow_00.html

Simon.

The example shown shows some massive bracing preventing the side walls from being forced out by the weight of the vault. Unfortunately no attention appears to have been paid to supporting the end walls, particularly the back, from being forced out by the expanding vault. End walls for kilns and ovens should be built under rather than beside the vault for this reason. People often think a barrel oven is easier to build than a dome, however it's instability and need for bracing end up making it more difficult to build than the self supporting hemispherical dome.

[downunderdave]

Feb 29, 2016 18:24:36 GMT yaffle87 said:

Hi there,

I wonder if theres some help I can get here;

My build is about 64"x52" (outer) 45"x32" (inner)using reclaimed Storage heater bricks for the hearth, with a sand and clay rich soil sub-floor. I have just enough firebricks for a side-end arch with a chimney outside door to contain steam effectively. I plan to clad the outside of the oven with an insulation layer of clay rich soil/sand, vermiculite and an outer cob layer with lime finishing plaster with a good amount of space around the door. I have had trouble with high ceilings in pizza ovens and want to make a more dedicated bread oven with a lower crown that I can use for small scale market baking as well as pizzas etc for supper clubs.

I have built many cob and fire cement pompei style ovens but this is my first try using brick arches, which I have no experience with.
I need advice on whether its possible to make the crown of the oven as low as 12" with the width of the arch being 32", with standard firebrick - I could afford to get a few keystones or some tampered bricks for edges but trying to keep cost right down and use what I have. this is bearing in mind the weight of a 6-8 inch cob and insulation layer on top of that.

The other thing Im deciding is whether to get cal sil board or not, Ive layed foundations and built a breeze block plinth and am going to start on a wooden base and surround for the sub floor. I would prefer to just make a hefty 6-8 inch clay/sand sub floor with enough heat retention for 2-3 bakes - I have plenty free clay but just wondering if I need a fire board to stop any heat loss underneath perhaps?

I will upload some pics if neccessary - Im currently scavenging all the leftover breeze blocks from my neighbours skip which is great and has done the job with the plinth, as well as around a ton of good clay from my garden. hope to keep all costs well under 200 smackers, have a load of leftover fire bricks from kilnlinings from my previous builds too but may need to purchase a few more, probably Vitcas without minimum order??.

Any professional advice much appreciated!

cheers

When you say "... For small scale market baking as well as ...supper clubs" does this mean you intend it to be trailer able? If so you maybe asking a bit too much of a low dome brick and cob construction.

[simon]

Mar 1, 2016 10:20:28 GMT downunderdave said:

The example shown shows some massive bracing preventing the side walls from being forced out by the weight of the vault. Unfortunately no attention appears to have been paid to supporting the end walls, particularly the back, from being forced out by the expanding vault. End walls for kilns and ovens should be built under rather than beside the vault for this reason. People often think a barrel oven is easier to build than a dome, however it's instability and need for bracing end up making it more difficult to build than the self supporting hemispherical dome.

The use of steel in this way does not prevent you from building the end wall under the vaulted roof.

Shallow dome 'Neopolitan' pizza ovens are also sometimes braced with steel to support them.

Another type of oven with a shallow roof is a bagel oven. Check out this one Alex Chernov and his team built for Best Ugly Bagel.

Best Ugly Bagel Oven

Note at 2:38, and at 3:00, you can see the bracing.

It's the shallowness of the roof that causes the problem, 'yaffle87' wants a shallow roof, steel allows you to do that.

[yaffle87]

Cheers guys,

Simon, I have some steel strap stuff and some tighteners that I will use to support it in that case I think. Stovemasters make some awesome looking ovens. What happened to Turtle Rock, they built some beautiful Guillard ovens in north America but they seemed to have dissapeared?

Any ideas on Calcium Silicate board and if its needed? Im pretty sure I will save money and go without?

Dave - I already have a mobile pizza oven that I made from fire cement and lime on a custom built trailer I use for outside catering so Im all good this is just to bake bread at home and take to markets for now and to run pizza nights and supper clubs in the garden:

  

I also need to decide on a door design for the brick oven, Im thinking 3 inch wood covered in steel plate with a lip to keep it flush?

[simon]

If you're trying to support a barrel style oven, you need a rigid beam of steel. Steel strapping doesn't sound suitable.

In all honesty, given your needs, I don't see the need to go for such a shallow oven.

If you're on a budget then don't use CalSil. Do insulate though.

[downunderdave]

Mar 1, 2016 20:45:43 GMT yaffle87 said:

Dave - I already have a mobile pizza oven that I made from fire cement and lime on a custom built trailer I use for outside catering so Im all good this is just to bake bread at home and take to markets for now and to run pizza nights and supper clubs in the garden:

  

I also need to decide on a door design for the brick oven, Im thinking 3 inch wood covered in steel plate with a lip to keep it flush?

Nice set up. I thought mine was small, but I think yours is smaller.