Benjamin Dinkel

Hi Cedric,
I don’t know how hot the bell outside gets. I’m sure some of the Permies with a bell in their house can answer that.
But I have some questions that might help us get closer to the answer.

Is it structurally necessary that the ladder/staircase touches the bell? Does the fireplace support the stairs?

Could you make the bell slightly smaller, leaving a gap?

You could also put insulation between the bell and the stair.
Or maybe insulate a bigger part on the inside of the bell around where it will touch with some super wool.

Today I made some more cob with the harvested clay, replaced the 5-minutue-riser with a riser made from dense firebrick and raised a layer of (insulative) cob around the core.
Also I had the idea to put a tile with a cutout on top of the feed tube to give it some stability.

Yesterday I went and harvested some clay from a site a friend of mine, being a geologist, was happy to point out to me.





Cracked soil is a good indicator for high clay content





The clay soil was really hard to dig, hard as a rock almost





It's good clay though, and after re moisturizing is nice to work with and has almost no stones.

Ok, will do.
I’ll keep you posted on the progress.
Thanks for watching out!

Hi and welcome to Permies!
In any cob mix you want clay, sand and fiber. So a good first step would be to make some test bricks from the soil you have. Just make it into a workable moist mass and form some "pucks". After drying see how much they crack and how much resistance they have to compression.

Could you elaborate more on the project you have in mind? A lot of the answers are "it depends", so it really depends on what your plans are.

Hey guys,

good point. Would you care to elaborate what the difference is? Why does it work for a stove but not an oven?

As I understand it the carcinogens come from breathing in very small particle things?

Hi Thomas,
I've seen your oven and it's really cool. Black and white function especially.

I have also seen Matt's riserless cores, but wanted to first go more traditional.  

One of my design goals was a pizza stone and a round cupola.

I'm giving it a go at building a rocket powered, black pizza and bread oven.
You can check the progress here: Cob-brick-oven-rocket-technology

This build got unfortunately cancelled.
In November I'll build a similar J-Tube for someone else and will probably use the metal parts on that one. I'll start a new thread with questions and documentation soon.

The bricks will get used much sooner in my first attempt of combining the aesthetics and the durability of a cob and brick oven with the rocket technology. You can check out the progress here: Cob-brick-oven-rocket-technology

I have, after way too much pondering, finally started the construction of my cob and brick oven powered by rocket technology.

It will be a black oven.
A big clay tile will be positioned over the riser and act as a pizza stone.

The power will come from a 6" J-tube built in dense firebrick and a "5-Minute"-riser.
Dimensions (inside) are feed 27 cm, burn tunnel 62 cm, riser 85 cm.
Exhaust will be 150 mm pipe.


I have an open ear for any questions and suggestions!


Yesterday I put down some foundation to keep the construction off the ground (there's sometimes rainwater washing down that path).





Then a layer of expanded clay bound with lime.
Then sand for an extra level bed for the core.






Then I built the core, sticking everything with some clay slip and adding some cob (actually more clay mortar, no fiber) on some of the joints.






I also researched how to use my laptops webcam to take time lapse photos (1 every 5 s). So I'll compile a time lapse of the build. Unfortunately I took a single photo the first day instead of starting the time lapse.