Cob,  Gardening adventures,  Permaculture and Edible Forest Gardening Adventures,  Ponds

Cob Oven, Part One

Levelling the firebricks

Today six members of the San Diego Permaculture Group converged upon my property to build a cob oven.  No, not with corn cobs.  Cob is an ancient building method that is similar to adobe, but without the brick.  Cob buildings, some of them several stories high, have stood for centuries in as diverse areas as Turkey and Wales.  Building a cob outdoor baking oven is a good exercise in cob building that is useful and easy.  None of the members, nor my daughter who jumped right in to help mix mud, had made a cob oven before.  That was okay, because neither had I!  Using as a reference the book Build Your Own Earth Oven by Kiko Denzer, and having watched several YouTube cob oven videos, we set off on our learning experience with the energy and fellowship that this newly formed group radiates.

Because of all the deconstruction on my property, building materials were at hand.  I decided to set the oven on a cement platform left from a torn-down shed.  That eliminated digging and filling a drainage base.  My son had helped carry bags of sand down to the work area, which besides straw and wood shavings were the only items I purchased for this project.  With broken concrete and cinderblocks, the group made a circular base about two and a half feet high.

The base made with cinderblock and cement chunks

The height helps the back of the baker, but if the oven isn’t used all day every day, a shorter one isn’t going to be a problem.  Especially for a short person like myself.  Not that short, but short.

When I moved onto the property there was all this gravel and stone around.  I hated it.  I removed a lot, but much disappeared into the pathways.  Some has resurfaced with the tilling that has been done to loosen the soil and add mulch.  We gathered a lot of the stone along with some dirt and used it to fill the base.

Then we made some rough cob.  There was a pile of hard clay that came from the pond excavation.  In fact, the bottom of the pond, which is unlined because of the clay content, is almost pudding-like in consistancy with the silky clay.  How do I know?  Well, let’s say that on a hot day this last week I got to know my pond a little better.

Collecting clay samples with my feet

Anyway, the clay contains really hard lumps.  It will make wonderfully strong cob, but first it has to be broken down.  My daughter filled a wheelbarrow with it, then we dumped it out onto a tarp and added water, expecting it to be easy to mix when wet.  Wrong!

This insulation batch is made with clay, sand and wood shavings

We added a lot of water and some sand, and mixed pretty well, then added some wood shavings to it for tensile strength.  This was used to gap holes in the oven stand and form a base for the insulation.  The insulation was made of the flat vodka bottles somebody in the history of this property obviously preferred, along with a broken necked Coke bottle that were found when the pond was excavated.  Pretty cool, huh?

A treasure of old bottles
Bottles were layed on cob for insulation

Meanwhile, another wheelbarrow was filled with clay and water, and a group started using their hands to mix it and disintigrate the hard lumps if possible.  This took a long time, and still there were lumps.  The scene looked like the part in Moby Dick when the whalers are kneeding the blubber with their hands, only a lot less gruesome.  This clay mix must be smooth for the next step, building the oven itself.

Finding the lumps in the clay









On top of the bottles went a layer of sand, which was levelled as best we could.  On top of that went firebricks, which were also levelled.

The firebrick was layed on sand


At this point we stopped due to time.  The whole process was only a little over two hours long. The wheelbarrow of prepared mud has been covered, as has the oven base.  In the very near future we plan to reconvene and make the rest of the oven.  After that… pizza!

Everything was even except the middle



    Good for you. It is a lot of fun, hard work. I hope you have helpers. We’re going to cob the insides of our chicken tractor, which doesn’t have insulation for the girls. It should entertain the hens, at least!

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