Hybrid Oven: Brick Walls with Cob Dome

[mfugee1234]

I was wondering if anybody has ever made an oven with refractory brick walls and a sand/clay thermal oven dome? I originally wanted to make an all earthen/cob oven, but when i found out how many cracks form using all clay, i revised my plans. So far for the thermal layer, i have built the walls about 12.5 inches high using refractory brick. Its currently in a "U" shape.
My next step is to build the dome using a clay/sand mix. My question is, if i use a clay slip & saw dust mixture for the next layer (Insulation), will the insulation mixture stick to the brick like it will the clay dome section? Also, do you see any potential problems that could happen? I'm think if the bricks expand faster/slower than the clay dome section, it may cause unnecessary cracks. Any advice or comments would be greatly appreciated. i will also post pics later for anyone that would like to try this hybrid oven.

[Tscarborough]

Re: Hybrid Oven: Brick Walls with Cob Dome

You would do better with cob walls and brick dome.

[cobblerdave]

Re: Hybrid Oven: Brick Walls with Cob Dome

Gudday
Firstly I am a brick oven builder but I have had contact with clay ovens.
I have never heard of brick walls topped with clay. I have seen brick hearth with a border of brick to protect the dome from damage from peels etc. the dome was cracked along the connection between the two as would be expected. My thinking would be that the clay dome has its strength due to it being I piece resting on the hearth. Breaking the dome into two different materials so high up would just lead to it failing at that junction. Tscarborought is certainty right in saying that the dome would be better bring brick on the top this is always the hottest and most stressed.
You have got this far with brick why don't you just finish the whole dome with brick.
Regards dave

[mfugee1234]

Re: Hybrid Oven: Brick Walls with Cob Dome

that sucks to hear but thank you both for your input.

[cobblerdave]

Re: Hybrid Oven: Brick Walls with Cob Dome

Gudday
Now I remember you , your the bloke who made the mini oven which cracked when you were curing it. Your really determined to build an oven with materials from your local environment ... That's cool.
On the way to building my oven I would have liked to do that as well but the local environment ( sub tropical Australia ) is a bit cruel on cob ovens ( 30 in rain this year 22 in the first 2 mths).
I had the idea to build with commons but they are not common since most of the housing is basically hardwood frame with hardwood cladding on stilts. Modern stuff is brick veneer and modern brick is not suitable.
So my oven has a heart of firebrick and some ceramic insulation and the exterior of reclaimed and salvage. Suits me just fine. Sometimes you just have to change things.
One of the coolest ovens I know is made of a mix of things. The hearth is possibly firebrick reclaimed from an old boiler. The dome was built of local commons built on a sand mold. The insulation is clay and straw with compressed fiberglass over that and all finished with a dome of reclaimed house brick ,pavers house roof tiles. It doesn't have an entrance proper but rather a hood made of 2 brown baked enamel range hood out of the 70s. It cooks well and I eaten bread out of this oven.
Anyway enough of my ramblings why don't you keep all of your build to a single post so its easy to follow. Keep it in this section and you'll also get a following.
Forno has the best home built ovens builds on the planet ... Period .. But the important thing is to encourage all

Regards dave

[mfugee1234]

Re: Hybrid Oven: Brick Walls with Cob Dome

Gudday
Now I remember you , your the bloke who made the mini oven which cracked when you were curing it. Your really determined to build an oven with materials from your local environment ... That's cool.
On the way to building my oven I would have liked to do that as well but the local environment ( sub tropical Australia ) is a bit cruel on cob ovens ( 30 in rain this year 22 in the first 2 mths).
I had the idea to build with commons but they are not common since most of the housing is basically hardwood frame with hardwood cladding on stilts. Modern stuff is brick veneer and modern brick is not suitable.
So my oven has a heart of firebrick and some ceramic insulation and the exterior of reclaimed and salvage. Suits me just fine. Sometimes you just have to change things.
One of the coolest ovens I know is made of a mix of things. The hearth is possibly firebrick reclaimed from an old boiler. The dome was built of local commons built on a sand mold. The insulation is clay and straw with compressed fiberglass over that and all finished with a dome of reclaimed house brick ,pavers house roof tiles. It doesn't have an entrance proper but rather a hood made of 2 brown baked enamel range hood out of the 70s. It cooks well and I eaten bread out of this oven.
Anyway enough of my ramblings why don't you keep all of your build to a single post so its easy to follow. Keep it in this section and you'll also get a following.
Forno has the best home built ovens builds on the planet ... Period .. But the important thing is to encourage all

Regards dave

Hi Cobblerdave,

You must be thinking of somebody else. I just joined Forno Bravo yesterday cause i started panicking about a build im already 1/3 of the the way into. I already bought the materials for the original design and am just trying to do damage control until completion.

Since the brick walls are already laid out/mortared in a "U, i was thinking about adding a thin (1 1/2 inch) cob wall outside of the bricks. once the bricks end, i will then make the cob 3 inches in width. My thinking is that if the cob starts from the ground and continues to the dome, then it will have more structural integrity. I know this is hard to picture so i added an attachment of of the design i'm talking about. Thanks so much for the help thus far.

[cobblerdave]

Re: Hybrid Oven: Brick Walls with Cob Dome

Gudday
Sorry about the mistake.
Have you already mortared those bricks in with Portland cement based mortar? Or a lime based mortar ? If Portland cement only it will fail. No if,buts,or maybes it will break down with the temps in you oven. Sorry for the bluntness but its fixable at this stage not after without a big effort
Regards dave

[mfugee1234]

Re: Hybrid Oven: Brick Walls with Cob Dome

I used a sand, clay, lime, portland cement ratio of 10:6:3:2. Did you have any suggestion on the oven design i attached? i got the idea from the sunset magazine article where they used both brick and adobe (its modified though). The only thing is that i can not find any comments, good or bad, from people that have actually made this Sunset design. So I'm hoping the FB community could potential problem/solutions i should be thinking about. Thanks so much thus far Cobblerdave!

Build an Outside Oven - Sunset.com

[Tscarborough]

Re: Hybrid Oven: Brick Walls with Cob Dome

You should just proceed as planned. It will work fine. Certainly there are other ways, but you will, if nothing else, gain experience and when done be able to cook some pizza and bread (among other things). Then if you decide that you really do enjoy it more than you thought, you always have the option of going back and building to a different specification.

edit-move the chicken wire to the outside of the vermicrete layer and embed in either clay or cementious stucco.

[cobblerdave]

Re: Hybrid Oven: Brick Walls with Cob Dome

Gudday
I took the time to read the plans... cute little oven and sounds achieviable.
I recon you'll enjoy building that. see if you can post some pics

Regards Dave

[david s]

Re: Hybrid Oven: Brick Walls with Cob Dome

Unfortunately the plan does not go on to tell about the importance of the water elimination from a cob oven. If the water in the centre of the walls suddenly turns to steam it simply pops and blows the arch apart from the centre. Because although it may appear dry on the outside the clay will still be moist in the middle. To help with the water elimination you can add polypropylene fibres which melt at 160C and provide a network of mini pipes that water vapor can escape through. However you should wait for around three weeks to allow sun and wind to do much of the work for you, covering if it looks like rain. The plan doues not say anything about removing the cardboard cylinder so it presumably stays in place and burns away. This is an easy approach, but does not help the arch dry from the inside. Proceed really slowly to eliminate water from the clay to prevent failure. Good Luck.

[mfugee1234]

Re: Hybrid Oven: Brick Walls with Cob Dome

Thank everyone for the input. Its a bit overwhelming taking on a task a bit blindly. I will definitely post pics of the project.

[mfugee1234]

Re: Hybrid Oven: Brick Walls with Cob Dome

You should just proceed as planned. It will work fine. Certainly there are other ways, but you will, if nothing else, gain experience and when done be able to cook some pizza and bread (among other things). Then if you decide that you really do enjoy it more than you thought, you always have the option of going back and building to a different specification.

edit-move the chicken wire to the outside of the vermicrete layer and embed in either clay or cementious stucco.

Just to clarify, should i replace the vermiculite layer with a clay insulation layer instead? Also would you recommend adding chicken/mesh wiring in the 1st (thermal) layer and 2nd (insulation) layers for added support or just the 2nd layer?

[Tscarborough]

Re: Hybrid Oven: Brick Walls with Cob Dome

Like this:

[Laurentius]

Re: Hybrid Oven: Brick Walls with Cob Dome

The vermiculite layer is the insulation. What is clay insulation??