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It started with cob. I have always been interested in natural, alternative, inexpensive, and
do-it-yourself building techniques. Things like timber framing, straw bale, and rammed earth building. While surfing alternative building sites on the internet, I learned
about cob. I had never heard about cob, it sounded interesting. Just dig up
some sandy clay soil, mix it with water and straw, build a house! Well, a house might be
a bit much to start with, maybe try something smaller, just to get a feel for it.
What could I build that was small and useful? - An OVEN!
An earth oven would be the perfect project to get to know about building with cob. And an earth oven wouldn’t take too much work. It would be useful and fun and great to make pizzas and bread. I have the perfect spot for an earth oven, next to my fieldstone patio and fireplace. Part of the foundation was already there as a curve in the patio that fit the foundation outline nicely. While thinking about building an earth oven, I happened to take a trip to the Yestermorrow design build school near Warren, Vermont. There they had an earth oven, with a sculpted tree trunk as the chimney. I purchased Kiko Denzer’s book Build your own Earth Oven from them also. We ate dinner later at the nearby American Flatbread Co. where they make incredible pizzas in a big earth oven inside a barn. This was all the inspiration that I needed. When I got home I immediately started digging my foundation and gathering rocks for the base. |
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I dug down about 2 feet to provide a solid foundation. I wanted a good strong base that looked good and would last long time. The earth oven, with its stone base will be very heavy, and I didn't want it to shift and crack. The frost line here is supposedly around 3 feet, but 2 feet is deep enough to get to stable soil that won’t be heaved by frost. I used 3 bags of Sack-crete concrete mix to provide a solid footing to begin laying the rock foundation. |
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I went rock collecting 3 times, filling the back of the van until the springs were near bottomed out. The pile of rocks I had to build the foundation looked enormous, but all but a small pile of odd-shaped rejects were used. The rock foundation is a little over 4 feet in diameter and about 4 feet tall - 2 feet in the ground and 2 feet above ground. I layed the stones in cement mortar, and kept the mortar raked well back from the face of the stone for a more natural look. |
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The rock foundation was hollow in the center, and this hollow was filled with various things as I built it up. At the bottom, I used a layer of coarse washed gravel to provide good drainage for any water that might find its way into the foundation to easily leach out. Most of the hollow was filled with sandy gravel subsoil dug from the hillside behind my garage, and some extra odd shaped rocks not used in the walls. I added the filling in layers as the walls rose, packing it down well by pounding with a timber to prevent settling. |
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The top of the rock foundation received a special filling. I had a bag of pumice lava rocks sold for landscaping, and thought that a layer of this would provide some insulation below the sand and firebrick floor to help the oven hold heat longer. Above the lava rocks was a 4-inch deep bed of well-tamped sand that acts as a setting bed for the firebrick oven floor.
The sand was carefully leveled and tamped solid to receive the firebrick floor. I was able to scrounge some used firebrick from Grandpa Elton, and purchased 15 new ones, for the total of 21 bricks needed. I laid the bricks tightly together in a basket weave pattern, with 3 bricks forming the doorway hearth. |
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The sand that forms the void was packed and shaped to a beutiful pregnant dome. The sand was collected from a sandbar under a bridge in the forest. A lovely time spent collecting 12 five-gallon buckets of sand. This void is 27 inches in diameter and 16 inches tall. |
Any questions or comments?? then....
E-mail me!