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Barrel oven, encased in cob

 
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Hey yall.
So i'm developing a plan for an outdoor kitchen: (barrel oven, rocket stove, and a griddle bbq setup of some sort. At first I was wondering if all could be powered by one J-tube. hot air going up riser, into one end of oven chamber around and out into a tunnel with an opening for a stove, a griddle, and finally a looong chimney at the end. Now I don't feel too confident that exhaust would be hot enough to be of much use after going through the oven system.

So now I think I will give each feature a separate core, but I'd like to keep them aesthetically part of the same cob "form". I know that most rocket ovens have a metal outer layer, which makes sense bc of contraction and expansion. I've been looking at this oven https://www.firespeaking.com/videos/wood-fired-barrel-oven-video/ , it's not powered by a rocket core but other wise seems like a similar idea. If I built a brick cavity or was able to make the outer cavity of just cob somehow, is it likely that this thermal mass would affect the technology in some other way?

Thanks,
Sophie
 
Rocket Scientist
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That was a fun video I expect a cob surround similar to that would work fine. It would not lose heat any faster than a metal outer skin, and after some heating it would probably retain heat and help keep the oven warm.
 
master pollinator
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Offhand, I wonder if the expansion/contraction of the metal in the barrel would mess up the bond with the cob and interrupt the heat transfer. It's still way better than naked steel though.

I have seen quick-and-dirty cob-and-barrel ovens, but the cob was stuffed on the inside of the barrel with a heavy duty expanded steel mesh to hold it in place.

Edit: I just watched the video. It's a different approach from what I visualized, but I like it.


 
rocket scientist
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Location: latitude 47 N.W. montana zone 6A
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Hi Sophie;
Here are a few photo's of my Rocket powered all brick Black or White oven.
Construction is ongoing and I will have photo's of the build itself later.

I smoked several chunks of white cheddar cheese in this oven yesterday as its first meal produced.
20210627_100339.jpg
[Thumbnail for 20210627_100339.jpg]
20210629_073831.jpg
[Thumbnail for 20210629_073831.jpg]
20210629_073917.jpg
[Thumbnail for 20210629_073917.jpg]
 
Douglas Alpenstock
master pollinator
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Mmmm, smoked cheddar. Awesomeness! What's your preferred wood for smoking?
 
thomas rubino
rocket scientist
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Well my preferred wood is Hickory , but it does not grow here. So I can only get it when someone brings chunks back for me.
However we do have plenty of mountain maple (vine maple)
I use it almost exclusively with cheese.
I have apple and cherry on hand as well.
 
Sophie Gell
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Thanks all! I will have to make a temporary frame for the cob or brick out of willow, or plywood. It seems that, understandably, the expansion of the metal frame causes the masonry to crack/shift over time. Do you tend to use high refractory materials for the j-tube as you would on an RMH? It seems most people are just going with regular brick. What did you use Thomas?

Additionally, I've been binging a lot of youtube videos of wood cookstoves like this:  

I am surprised that the fire would come out of multiple places and still remain strong enough to heat the pans. Do you buy it?
 
thomas rubino
rocket scientist
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Hi Sophie;
There are over 300 plain clay bricks in my build.
There are also apx 40 split fire brick, that are needed in the core area.
No refractory cement was used at all.
The lowest levels of the clay brick surround are concrete mortared and all the upper levels are fireclay/sand mortar.

Nice video.  That is an L tube design.
As the holes are covered it sends more heat down the line, heating the chimney stack and creating a solid draft.

L tubes require steady attention to keep the fire hot.
A J tube design is the same but is self feeding with vertical wood.

 
Sophie Gell
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Wanted to post an update on this project!

We got very far, then a set back. Looking forward to finishing in the spring.

It's a 6.5" J tube powered rocket oven, but as stated in the title, we used cob as the shell. For the metal fabrication of the inner barrel, I followed the permies plans exactly. The J tube dimensions are somewhat unique, as they have to be so that the oven is not too high.

Fabricating the metal frame to hold the barrel 2" above the riser was rather tricky. Constructing the armature to support the cob out of Luan, was easier than expected and seems to have worked well.

Once it was cob time, it was pretty much smooth sailing. Until the rainstorm. I was planning to do a 'smoothing coat' of just sand and clay to set the tiles into. Then come back in the spring to plaster when it warmed up again. Well I did that, and then a very windy thunderstorm blew the tarp off and set me back quite a bit. Lost a good amount of material, it just slid right off under the weight of the water and gravity. I threw what I could back on, expedited the roof. And now we are on hold until spring. Will update.

I did get to fire the oven a couple times, got it to 350 without trying too hard, and it was still wet. I am hoping for much higher temps. The exhaust was very hot, so I installed a damper but haven't tried it out since. Felt like walking a fine line between wanting to fire to dry up the cob shell, but not wanting to burn out the armature before cob could support itself. In the end not sure it mattered much.
 
Sophie Gell
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pics!
Barrel-Oven.png
early sketch
early sketch
grinding-toxic-waste-out-of-barrel.jpg
barrel held one of two part insulation foam chemical, left a hard film that had to be grinded out.
barrel held one of two part insulation foam chemical, left a hard film that had to be grinded out.
metal-fab.jpg
followed permies barrel oven design closely for this part
followed permies barrel oven design closely for this part
wood-base.jpg
pressure treated for the base
pressure treated for the base
cobbing-in-j-tubes.jpg
J tubes go in. Thanks friends
J tubes go in. Thanks friends
frame-for-barrel.jpg
This was tricky
This was tricky
-manifold-.jpg
this are is deemed the manifold
this are is deemed the manifold
barrel-set.jpg
barrel mounted
barrel mounted
building-up-manifold.jpg
building up the side of the manifold
building up the side of the manifold
frame-for-cob.jpg
luan armature
luan armature
hardibacker-o.jpg
hardibacker will support a cob facade
hardibacker will support a cob facade
making-prgress.jpg
okay..
okay..
getting-somewhere.jpg
okay..
okay..
cobbing.jpg
cobbing
cobbing
getting-somewhere-two.jpg
fully cobbed oven
fully cobbed oven
smooth-coat-and-tikles.jpg
smooth coat and tiles on
smooth coat and tiles on
Frost-on-Oven.jpg
uh oh, running out of time
uh oh, running out of time
from-the-back.jpg
[Thumbnail for from-the-back.jpg]
rain-damage-on-oven.jpg
big storm :( annnnd now its winter
big storm :( annnnd now its winter
rain-damage-on-j-tubes.jpg
repeated freezing and thawing of wet cob doing some decent damage
repeated freezing and thawing of wet cob doing some decent damage
Oven-gets-structure.jpg
roof non-negotiable
roof non-negotiable
 
master pollinator
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What a shame that storm set back your beautiful work, Sophie! It will be wonderful when it's finished.
 
please buy this thing and then I get a fat cut of the action:
An EPA Certified and Building Code/UL Compliant Rocket Stove!!!!!
EPA Certified and UL Compliant Rocket Heater
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