Hello! Welcome to our four part series on how to build your own cob oven. This is our very first attempt at building with cob and we by no means know what we’re doing. Please use these posts as a rough guide and learn along with us. If you are interested in building with cob, we strongly suggest finding a “hands-on” workshop to participate in.
Let’s get started!
(8) 50 lb. bags of sand
(3) 50 lb. bags of “fire clay” –this measurement may be different if you are using natural clay
(1/4) of a bale of straw or dry grass
(45-50) red bricks or fire bricks –fire bricks are better, but not many stores keep them in-stock
Insulated base or stand to build on
Tarp –canvas or plastic
First, find a suitable location for your cob oven. We picked an unused section of the yard close to the house and without any tree limbs hanging overhead. Keep in mind that this oven will be getting very hot and fire safety should be your first concern when choosing a spot. It helps if the area is somewhat level too.
We decided to repurpose logs from around the property to build our base instead of buying extra bricks or stones to build it. Mark off your area! We used spray paint to mark off a circle so we knew how big to make our ring of logs.
Build up your logs or stones or bricks as close to your waist height as possible. Building the stand at waist height will make it more comfortable to use the oven since you won’t have to bend over too far. We couldn’t quite reach waist height, so we built up our ring as tall as our tallest log (about 2 1/2′ feet tall).
Then we filled the center of the ring with dirt and packed it down. Remember, our dirt has a very high sand content so if you do this be sure to use lots of sand as an insulator. Many people use a thick layer of sand and glass bottles to insulate the base from the heat of the oven.
We also added a layer of concrete slabs to help insulate and to create a level surface for the red bricks. I’m pretty sure these aren’t rated for high temperatures so I hope the red bricks will be a thick enough layer.
Next goes the layer of red brick. I also marked the size of the interior circle with chalk so that when I started building the core with sand, I would know the diameter needed. The diameter of my interior circle is 30″ inches. This measurement does not count any of the wall thicknesses… Just the inside of the oven. The outer circle is the 3″ inch thickness of the first layer. That way I know where to start.
Keep reading for “step 2” coming soon!