On the farm where we’re living, they intend to build some cob houses. Cob is a building method that uses clay from the ground mixed with sand, straw and water. You make mud balls and press them into shapes and let them dry. It’s like giant pottery. Anyway, we have never built anything with cob, so we decided to get some experience before embarking on building a house. We have started building a cob oven.
We started by clearing the grass away and putting down a weed barrier and rock. We then placed cinder blocks in a pentagon form on them. There is nothing magical about the pentagon, but we thought it looked cool. I think we could have done this in cob to save money, but it would have taken a long time to make that much cob and build that.
We then took bigger river rocks and placed them around the base of our pentagon cinder blocks. This will the the foundation of our structure so that water does not wick up the cob. It’s just like a house, the walls can’t touch the ground or you end up with big water problems. Especially in Washington State.
The dirt we had dug from the subsoil had varying degrees of clumpiness. I didn’t get a picture of it, but we smashed the dirt with a rock or stick to get the big clumps out before screening it to get a nice mixture of clay particles.
You then mix the clay with sand and add a bunch of water and mix it up. With the quantities that we are making, the only real way to mix it up is to dance on it. Then you add straw and dance some more. We need some music because it was tough to dance without music. The kids really enjoyed playing on the mud, but they did not weight enough to really get the stuff mixed well.