THE EARTH OVEN, PART TWO…
The next stage of oven building was to either remove the sand dome, or to add on the insulation layer. I think I forgot to mention that before work halted on the original workday, a door had been cut. There is a particular, exact ratio of door-height to oven-height to which one must adhere in order to achieve a working oven. We had a 16″ dome, which meant that we needed an opening that was something like 9.12.” A piece of clay corresponding to the correct amount of area was excised from the wet clay of the first mud layer. The removed piece was then covered with newspaper, and re-inserted into position insulated order to act as a removable support for the clay as it dried. Large screws were inserted into the mud in order to act as “handles” so the piece could later be removed.
The insulation layer hearkened back to Bible stories time…straw had to be added to the mud/clay to make this layer. We placed mud and straw onto a tarp, got a hose, and some tightly attached shoes. We used our feet to work the straw into the mud. By pulling up on the tarp we were able to “knead” the mud, then press more straw into more mud, repeating this process over and over until a workable mess had been created. This was a lot of hard work, and brought up endless mental images of Hebrew slaves toiling in the Egyptian sun to make Pharaoh’s bricks….this particular technology hasn’t changed in millenia, and, the Hebrews were right….no straw = crappy bricks. This layer went on over the original layer, four inches thick. And at this point, the decision was made to not have just a simple oven…we were going to go for an extended oven opening (the correct term for this is a “plenum”, I am told), with chimney. So by now, we had about eight inches thick of both wet and dry oven mud, still with the sand dome inside. Somewhere in there I decided it was time to dig out the sand. This, like every other project stage, proved more time-consuming than one would anticipate. I used a gardening hand tool called a “Soil Scoop” to scrape the sand out. Sometimes it was slow going since we had packed the sand down quite firmly. Other times, large amounts fell loose. When it was all out, a small foxtail-type broom swept out the last of the sand….and, we left it to dry. Over the course of the next few days, we began to have really bad cracks on the inner layer of mud…if you peeked into the oven interior, it looked ugly. The cracks were so bad that one large oven section was almost broken free. I didn’t want to start all over again so I used more mud to patch those cracks, forcing lots of mud into the gaps…but in retrospect, this indicated a flaw in the original mud mix. We should have added some straw or long grass…something with fiber, in order to better reinforce that mud in the first place. But the damage was managed well enough.
Before the outer layer of mud dried too much, we realized that we had a problem with our door opening…it hadn’t been measured and cut correctly, and now that had to be fixed with the clay having already hardened. Oops. We tried using a Sawzall to go through the mud…which didn’t work well. Finally I went to the low-tech solution of a hammer and chisel. This worked fine, though I had to be careful not to hit the chisel too hard, and without too much effort the opening was re-formed and made smooth.
Now it was time to create the plenum and chimney, to extend the oven opening outward. This was done by taking a section of 4″ agricultural pipe (PVC) and wrapping a few thin sheets of wet newspaper around it. The pipe would be butted up against the oven opening as the form for the chimney, and it was important to make sure that the pipe could slip out once the clay was dry. This particular pipe had a flared end, and we made sure that the flared end was ON TOP, otherwise it would have been impossible to remove later. So we took more of our clay and straw mixture that had been prepared (by again stomping the two ingredients together on a tarp with water added as needed). We built the plenum and then about six inches of chimney around the PVC pipe. We rotated the pipe and let it dry for some days, and then carefully removed the pipe. Everything after this point was cosmetic. I wanted the oven to be “something”, a creature or some special shape. Original ideas ranged from a peacock, to a beehive, to a…..basically I stared at it for a long time until the shape of what was there suggested the finished item to me. This turned out to be a Sphinx. Not the Sphinx in Egypt, but the mythologically classic one that is the head and torso of a woman, feet-body-tail of a lion, and wings of an eagle. To make the sphinx, I mixed a finish plaster. This choice allowed for making the oven into a creature, as well as providing a measure of water resistance. We bought a sack of mason’s lime. I hydrated it and added sand, fine feathers and dryer lint (they functioned as a binder), and concrete tint. I mixed this caustic brew with a hoe, and it was very stiff and difficult to fully incorporate. If I could do it over, this would best have been done in a mortar mixer. Something like 7 gallons of plaster were created this way. I waited until the next day, then went to work. A gloved hand and a smooth carving knife were used to glob on the plaster and press/smooth it. There wasn’t really enough mix, so some areas are only a half an inch thick instead of the recommended inch. However, it held together even in thinner measure and adhered very well to the underlying dry mud. In areas where detail was called for, extra plaster was used to form features. The head of the sphinx encased the chimney of the oven…I thought through ahead of time about where each detail would need to be located. The finish plaster was very sculptable and could take a fairly fine level of detail, but dried somewhat quickly…there was maybe 30 minutes in which to create detail before the material began to harden to unworkability. A knife smoothed and shaped, and a stiff feather shaft cut relief-types of details such as wings. I can’t really offer “how-to” for sculpting as I’m not really sure how I do this. All I can say is that I have spent many years studying art and sculpture, taking note of shapes and proportions, and I’ve practiced on a lot of snow-people when the opportunity presented itself. If you can shape things out of clay, this should be do-able.
The very last stage was to fire the oven. Build a fire of sticks, get it good and hot, and at long last bake something. The firing sort of “sets” the mud, and this is the point of no return. I think many people fire the oven much sooner than we did but….done was done. This was a fun project, took a lot of time but very little money, and pretty much everyone should have one!