From HOMEGROWNer Andrew Odom
(The following post is about our experience making a cob oven. We built in the middle of the summer and that presented a multitude of problems. But today we fired it up and it worked and we are getting
ready to have homemade pizza for lunch. So it does work. The
construction details have been trimmed back a bit. However, feel free to
contact me for more detailed instructions on how to build an Earth Oven
that costs less than the 24 beer bottles I used in construction.)
I love pizza. Having lived in Brooklyn, NY for a while I can't NOT love
pizza. It was on every corner and as a photographer with little money it
was the most affordable meal most days. I have also recently taking to
making bread of all sorts. So in the spirit of DIY neo-homesteading
projects I thought an outdoor earth oven would be a perfect experiment.
And since we live in Georgia - home of red clay - I figured the
materials were just out in the yard so why not?
After a fair amount of research I decided we would build a small cob
oven that would hold two personal size pizzas or three loaves of fresh
bread. The cost was right in my estimation, we had nothing but time
really, and compared to masonry oven, a cob was more eco-friendly and
better for our diet as traditional concrete contains a small amount of
volcanic ash and dye.
As is my tradition the first step I took was to do a little research which I did with the help of Kiko Denzer’s Build Your Own Earth Oven, a small book covering the construction of cob ovens from the ground up.
So how did I actually build it? Well....
With little more than some Georgia red clay, concrete sand, what straw,
brick, some recycled beer bottles and old granite slabs, plust a little
wood, I had everything I needed to make my own oven. After familiarizing
myself with Kiko’s cob oven design, I began building the foundation for
my stove from the reclaimed granite slabs. The foundation served two
purposes I figured. It would raise the oven off the ground in order to
have it at a more convenient working height and it also provided a place
to store wood for burning.
A fire brick hearth with insulation
insulating layer of beer bottles in a wheat straw/clay mortar was
constructed on top of the foundation in a ring of cob and beneath the
firebrick hearth. The hearth, a simple arrangement of 12 firebricks (the
only real expense at $1.85/each), would serve as the bottom of the cob
oven, where breads and pizzas would bake directly. The hearth bricks
were carefully laid on a thin bed of sand, so that they could be gently
tapped to be firm and level.
Sizing the Earth Oven
After all my reading I felt like a 21" diameter oven would be perfect.
Anything larger would be larger than we needed and anything smaller
would be little more than a rocket oven. I have found today that our
oven heats up to about 550 degrees in less than two hours of solid
firing with good, dried, hard wood.
Making a brick arch and cob dome
Before building the actual oven dome, we made an arched doorway with
some reclaimed red brick, pebbles (for holding the bricks at an angle)
all mortared with a sand/clay mix. The cob dome (nothing more than a mix
of sand and clay at a 3:1 ratio) was carefully built up around a moist
sand form covered with wet newspaper and up against the brick arch. The
sand was piled out of the doorway after the dome had dried some.
NOTE: The door is a critical 63% of the cob dome height, or 10″ high.
(The dome is 16″ high, which is Kiko’s recommendation for cob ovens
across the board.) This one measurement is the most critical because it
allows the oven to actually draw. Because the door is left open while
the oven is firing, the cool air is drawn in, and hot air and smoke can
pass out the top half of the door. (A larger ovens would more than
likely need a chimney.)
After all the above steps are done I would suggest adding layers as
necessary. Because we built in the middle of the summer we encountered
cracking with our layers as the mud simply dried too quickly. We will
also need to add a final insulated layer made of earth clay, no doubt,
to ensure all the heat is retained and the cracking does not effect
cooking heat or time.
Overall, this oven has been a tremendous learning experiment and one we will continue to employ and expand on.
To see all the pictures from start to finish just visit this Flickr set.
You can also see the first firing by watching the embedded video below: