By Elizabeth Smith
If you love the taste of brick oven fired pizza and like to build things, this article is for you. At the Rita Ranch Community Garden, we are building an outdoor oven so we can make homemade pizza, roasted vegetables, baked bread, and more. Since our area is completely outdoors, our oven needs to be weather proof, easy to use, inexpensive to build, and fun to make so we decided to make an earthen oven out of “cob.” What is cob? Cob is finely screened, clay soil mixed with water and some straw. Our instructor, Beau Woods, taught us that cob is this wet mixture formed into whatever shape you need while adobe is that same wet mixture but formed into blocks and dried first.
To find the clay content of your soil, dig down 4-6” and take a handful of dirt and put it into a glass jar with twice as much water. Shake it up and let it settle back down for the next 24 hours. It will have several layers which will probably include water, then clay, and then the heaviest sediments and sand at the very bottom. You need 20-30 % clay for the best cob.
Using ¼” mesh, sift your soil onto a tarp. Form a basin in the middle of the pile and add some water. Now its time to add in the fun part by mixing it up with your bare feet. You could also use a cement mixer but where’s the fun in that? Add in about 5 % straw (not hay) and stomp away. Your goal is to make a thick mixture that doesn’t crack apart when you throw a clump of it in the air and catch it. Too wet and it wont stay in place but too dry and it wont stick together properly.
We marked a circle on the ground for how big our pizza oven was going to be and dug out about 4 inches of dirt from this area. Making sure the ground was level, we started laying a base of cinderblock and mortaring (with real cement) in between all the horizontal seams of the bricks. The outside of the entire oven will be plastered over with cob so it doesn’t have to be absolutely perfect. Be sure and fill the inside of the circle and inside the holes of the cinderblocks with regular, dry dirt compacting it all down. Then came a buildup of cob, bringing the height to within 6” of the oven base height. Visualize pulling a pizza out of your oven and see what height works for you comfortably and adjust accordingly.
Next, lay down a couple of inches of cob on the base of the oven and build up an additional ring of cob all around the outer perimeter of the circle. Add an inch of sand inside that perimeter and level it off. On top of the sand, you will need a bunch of same sized, empty, uncapped glass bottles (beer, soda, etc) laid down on their sides. This creates a pocket of air underneath your oven, adding more insulation to keep your oven hot. Cover the bottles with more sand, bringing the sand to the top level of that cob ring you created earlier. On top of this layer of leveled sand goes a single layer of fire bricks. These are bricks made to withstand the very high heat of an oven or a fireplace so be sure and only use these here.
Visit the Rita Ranch Community Garden to see this project progress and for the rest of the instructions, go to our YouTube Channel:
https://www.youtube.com/channel/UCxGqjq28c802OHeJHfJx2LA
Pizza Oven Materials list:
Oven: fire brick, sifted sand, bales of straw (not hay), cinderblock, cement mortar.
Options: double walled metal chimney pipe, granite or flagstone for a countertop, decorative tile pieces for the outside of your oven.
