Tuesday, July 31, 2007

The Second Layer

Last time we completed the first layer of the dome. This update brings us through the second layer. As you recall, the first layer is thinner with no straw added to the clay mix. The second layer is thicker and adds neccesary thermal mass to the oven.

We begin with more mixing. This time we are mixing true cob -- a mixture of Virginia red earth, sand, straw and water. Because I had some powdered Red Art clay on hand and little left over coarse grog from the first layer, I added it as well.

I learned an important lesson about oven-building collaboration. While these projects are great fun for the kids, adult helpers can actually make the project go faster and provide good company. In this session, I was particularly lucky to have two helpers with great attitudes and actual experience in working with clay. In the future, I shall encourage more adult collaboration in my oven building activities.

Here, Mr. J does the cobbers' high step with me.

As before, we patted the cob into mushy bricks to facilitate the orderly shaping of the second layer. At the beginning of the day, it seemed anything approaching a brick shape would do. By the end of the afternoon, Mr. J's standards had changed and the bricks seemed much improved in shape and integrity.

We laid the cob "bricks" in courses around the first layer. The trick is to proceed as though you are truly building one course on top of another, merely using the existing dome as a guide. Note how pressure is applied down and not inward toward the dome.

We mixed two large batches of cob and one tiny one just at the end because -- of course - we were a two bricks shy. Here, Ms. J and I put the last bits of cob in place.

The last order of business was to smooth the outside of the second layer using hands and a rocking motion with a flat board.

After drying out, which takes at least a few days, the oven is functional. However, a final layer of adobe plaster makes the exterior a little more presentable by, among other things, hiding the straw pieces. Next update will include photos of the "plastered" end product.

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