Cob Ovens/Heaters

Overview and building of the base

We (that’s me sunshine, who else, just nicer saying “we” and not “I”), are building a cob oven, two chamber incorporating a Rocket mass heater as a second means of firing. The stack will have copper coils and a system for heating water. In front of the oven will be a seperate rocket heater for boiling water for tea, as well as raising steam for cooking vegetarian food and making syrup from sugar cane.

The double chamber oven will serve pizza, breads, baking etc, and a young lady from Russia who grew up using wood fired ovens, will give us some demo’s.

Alex with oven 300x225 Cob Ovens/Heaters


So this is a similar basic oven, being constructed by Alex Ojeda in Jacksonville.

And yes Alex, 5+2=7. You should make 10 your target so we can get into the metric system. Keep up the good work.  🙂

Maya is proud of you. LOL….

Now carry on building, time waits for no man….


The front door is cedar. Will be backed by steel? Or ceramic fiber blanket?




So this is where we are heading..


image4 e1359938751516 225x300 Cob Ovens/Heaters

Oven in front of dome

image5 e1359939143274 225x300 Cob Ovens/HeatersThis is the first bread bake.


There’s some video’s and hints in the bake section.  Where did we go wrong.. LOL


Good fun this.


The oven was fired with the wood in the wood chamber and the rocket was fired up too. Incredible how little smoke was generated and temperatures got to over the top of the scale. (>900 F).




  Back to the building… 

overall view 300x225 Cob Ovens/Heaters

oven overall view

OK. The base of our oven is made from bags. Number of reasons: Same architecture as the dome,  bags are on hand and building technique is more or less standard. Filling was expensive and labor intensive. As it turned out, the base was stripped down for re-engineering (reinvention of the wheel..), so having a bagged base was a plus in this instance. We are also making trials with cobbing and plasters for the dome home eventually. Thats the main reason really.


M.T. bottles are used to fill in the base. We may also use them on the cobbing of the base. (Perhaps also use on the dome later). The top two layers inside of the base will be bottles and the cob is mixed with perlte or/and saw dust and wheat straw.

The PVC pipe on the fire bricks is at the back of the oven. Feeding into the back lower part of it. This will obviously be replaced by Steel pipe. The bucket will be incorporated as a feed chute. Playing with with arches to test the construction as well as vertical and upside down cobbing. In the end only the one Arch for wood storage which is on the other side, was kept in the base.



Viewed from the other side:

ie view 300x225 Cob Ovens/Heaters


Wood storage under arch.

Just playing with the arch really, practice for the dome.

Used a wedge box to make wedged bags for the arch.







ewn wege bag 150x150 Cob Ovens/Heaters

Arched wedge bag

This is the wedge box ….

wege box 150x150 Cob Ovens/Heaters

Wedge box


Note the wood splitting maule

Nice weight for tamping. Small too.

                                                   Sewn bag in wedge  box shown on right.





You contruct a box form for the making of wedged bags.

IMG 1239 300x225 Cob Ovens/Heaters

And the wedged bags are stacked over the form to make up the arch.

They can be filled less as you go up if you like.This will lower the height of the base, and you can see it in later photo’s.

These are 11″ custom made bags.

 There’s lots of stuff on bagging in the dome building section of the blog!








oven cobbing 300x225 Cob Ovens/Heaters

oven cobbing


Build up the oven base using standard bagging methods.

A layer of chicken wire was layed ontop of the bags before cobbing.

Living in Florida, I was amazed that Turkey wire was not available? .. yuk yuk ..

Cob was laid over empty bottles (two layers of them). The cob was made up from clay on the property, that was excavated for the septic tank. Coarse building sand, soil or saw dust may be added.

The first layer was made up of soil/sand and sawdust. Nice texture. Perlite, soil, sand and Wheat straw was used in the second layer covering more bottles. Every batch was tweaked, depending on clay layer.

The oven floor will be next, built from clay and sand. That’s below the fire brick.

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The base is being cobbed now, just to play with the cobbing.

Soil from the property was dug out and the clay seperated. A bucket of this clay made up the “soil”. To this two to three buckets of sand was added as well as some wheat straw and Perlite. This made a nice first sample:

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 The insulating mix was made with soil and perlite. Plenty of perlite. This was placed over the second layer of bottles. So the base has two layers of bottles as well as a layer of sawdust with straw and a layer of perlite. This will contain the heat inside the oven quite nicely? 

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The cob should be firmly pressed downwards and sideways to give a good bind with the other placed balls. It was pressed down nicely when the whole floor was covered. Race against the sun here…

0 Cob Ovens/Heaters

The rocket test was to see if the draw would be OK with an elbow in the stack. The longer stack gave a nice draw and will be fitted with ceramic fiber blanket as insulator. I ordered 6# density which is good for about 1200 F, but received 8# density. Overkill.
I have used it for many years in kiln building and the main concern here is to protect the bags (and people) from heat. The rocket firing bricks will be cobbed as well. Bricks only cost $1,49 a piece. Good price for a FB.

 This a start. Go to the oven building section for the next episode …


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  • wp socializer sprite mask 32px Cob Ovens/Heaters
  • wp socializer sprite mask 32px Cob Ovens/Heaters
  • wp socializer sprite mask 32px Cob Ovens/Heaters
  • wp socializer sprite mask 32px Cob Ovens/Heaters
  • wp socializer sprite mask 32px Cob Ovens/Heaters
  • wp socializer sprite mask 32px Cob Ovens/Heaters

4 thoughts on “Cob Ovens/Heaters

  1. luis

    hey mike, my name is Luis, i’ve been trying to get information regarding sustainable living in florida and seems that there is not to many people doing it, i guess due to state or county regulations on housing construction…Well i’ve be been looking to buy a piece of land in florida in order to build an earthbag house, do you happend to know where can i find information on which counties is permited this types of contructions? obviously i would like that information prior buying land.


    Luis D.

    1. admin Post author

      Sorry, I know only of Suwannee County. The further North the easier? It’s a matter of going to them? Perhaps somebody out there can shed some light?

  2. Alex

    Mike, this is fantastic. Seeing this oven project in production lights a fire under me 😉 We are building another cob oven next Saturday and I continue to build the food forest where you helped the other day. More projects than I have time for!!!

    See you soon!

    1. admin Post author

      Great stuff these ovens. The blog is updated daily on the ovens as I am focussing on completing the project asap as the Dome is standing. (At least it didn’t fall down hey .. lol) I am also using the Permaculture techniques that you and Valerie shared and the garden remodeling is also ongoing. Fantastic stuff you guys do!

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