|
 |
When the first layer was finished, I used a notched trowel to roughen the surface, so the next layer would bind to it better. We let this first layer dry for 2 hot days, and came home to find some big nasty cracks across the dome. I figured that the mix was shrinking while drying, and the sand core prevented it from shrinking inwards, so it had to crack. The dome was drying well, getting quite stiff and leathery. I immediately cut out the door opening and scooped out the sand. The cracks, which were maybe 3/8" wide, then closed up quite a bit. I plastered the cracks shut. I let it dry another day, and built a very small fire inside, just to help it dry a little more. A collar of earth mix was added to reinforce the door opening. After another day of drying we started on the second layer.
|
 |
The next layer used a little different mix, more of a traditional cob mix: 1 bucket of Farnsworth redi-mix, 1/3 bucket of fairly pure clay, 1 bucket of sand, about 1 bucket of loose straw, chopped to 3 or 4 inches long, and enough water to make a good squishy mix. It was maybe a little to squishy, as it started to bulge again, and I stopped after building up about 8" from the base. During this time, it was hot and dry, and some more smaller cracks (about 1/16") were showing up in the first layer dome.
|
 |
We weren't able to work on it for 2 more days, so the lower part of the second layer got to dry quite a bit. The final batches of earth mix for the second layer were made with a little more sand, as follows: 1 bucket redi-mix, 1 bucket clay, 2 buckets sand, 1-1/2 buckets cut straw, water to make a little stiffer not so squishy mix. The first layer inner dome was getting pretty dry, so I dampened it and rubbed it with muddy watery soil mix to help the second layer bond. The second layer was finished, a full 4" to 5" thick over the 3" to 4" thick first layer, and smoothed and shaped by rocking and rubbing with a board. We left this layer a little rougher, with its straw stubble and small holes and joints showing, not completely smoothed out.
|
 |
I made this thick wooden door from a section of tree trunk, hacked into shape using a chainsaw, circular saw, and handsaw. The top photo shows the back side of the door that fits into the oven opening, the bottom photo shows the door in place. Over the next few days, I helped the drying along by building small fires and letting them burn out, not heating up the oven fully. A bunch of small cracks showed up on the surface, but the straw seemed to keep them small, short, and well distributed. After a week of drying, we were impatient to give the oven its first full firing and cooking test. |
 |
I filled the inside with lots of wood and fired it up. It smoked lots of smelly black smoke and had a weak flame. Fooling around, propping up a small section of 5" diameter stovepipe with an elbow on one end, I got a better draft and cleaner burn. Later after more firings, I found that a small fire, taking up only the middle section of the oven floor with lots of space around the edges worked better, burned cleaner, and heated the oven up faster with less wood. The stovepipe really helps with the draft, especially when the wind is blowing towards the door opening.
|
|
