Monday, August 23, 2010

First bit of cobbing

The power went out today, so we abandoned laundry and cooking and went outside and did a little work on the oven. We did a final laying out of the firebricks, adding a fourth brick to the front edge to accommodate future extra-large pizzas, and changing their orientation slightly. We tamped them down gently with the butt end of the wooden handle of a hammer to set them nicely into the compacted sand beneath.

Then we mixed up a small batch of cob. For our clay we eventually decided that a mix of 2 parts sand to 1 part clay was right. Or maybe 2 and a bit parts of sand. We mixed that together with some water, and folded in a bit of straw for tensile strength.

The idea today was to create a ring of cob around the fire brick to secure it during construction of the oven. We'll need to fuss around a lot on top of and around the fire brick to build the dome-shaped sand form, and to secure a thermal layer of cob over top of that. It won't be until the final thick insulating cob layers that the fire bricks will end up completely covered and enclosed in the walls of the oven. So in the meantime it's good to help them stay perfectly put by enclosing them in a ring of cob. It also gives us a chance to test out our cob-mixing ratios with a small batch. We mixed this batch in the wheelbarrow and it worked out well. Next time we'll be doing much larger batches and we'll mix on a tarp on the ground -- with our feet!

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