Recently one of my friends here invited a group of us to a natural building site he's been working on. He's attempted to describe his work to all of us, and we all have the same problem understanding because: 1) none of us actually know what houses are made of, therefore 2) we can't really understand or appreciate what is different about "natural" building.
"Natural" building refers to a range of building types, but in this case, in mainly refers to the walls. We were building two walls on Saturday for a greenhouse on someone's property. The first wall is going to be made of cob, because it absorbs heat during the day, and will radiate the heat in the evening when the temperatures drop. The second wall, which will be the back wall of an adjacent storage room, is made of wood but insulated with straw, rather than modern insulation.
While James and a few other friends were stuffing straw into the back wall, I was eyeing the cob mixture. I leapt at the chance to mix it up myself!
Cob is made of dirt and sand. The dirt and sand sits on a tarp. The best way to mix the two together is to pull one end of the tarp toward the other end, and then repeat in the other direction until everything is rolled up together.
Then it was time to throw some water on the pile and start stomping! It flattens out pretty quickly, so we'd pick up the tarp and roll the mixture around, then repeat the stomping.
After everything is pretty mixed up, and the consistency seems right, we folded in about one flake of straw, stomped, rolled the tarp some more, etc.
After some time, it begins to thicken and our builder-in-residence gives the OK that yes, this is good cob. The next step is to form it into balls and carry them over to the wall. Plop them right on there, and take care to stitch the cob mixture into the wall. I used my thumbs to press it the new cob into the dried cob that was below it. It's easiest to start on the outside and use one hand to make sure the side is nice and flat.
Meanwhile, the rest of our group was mixing straw with a mud-water mixture, called "slip", and stuffing it in the back wall. This is going to act as insulation inside the wall.
Their process was: Nail four boards on either side of the wall frame (the horizontal ones shown below), stuff with the straw/slip mixture, then pull up the bottom board on each side of the wall frame and nail it above the second board. Then repeat. The straw/slip mixture dries in the shape of the boards, so once everything is dry, the straw will be evenly distributed and nice and sturdy in there.
Just another weekend in North Carolina!