| Building Green on Your Own, Part 3 |
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Cob Cob is a mixture of sand, clay, water, and straw, applied directly to the foundation by hand or shovel, and then massaged into shape. Most of the work is done by hand or by simple hand tools. Walls are whitewashed, lime-plastered, or coated with earthen plaster to protect them from rain. Add insulation in cold climates. In rainy climates, protect the walls with large overhangs or durable plasters or both (lime/sand plasters are good). Earthbags This method uses the same polypropylene bags that are used to store and ship grain. Fill the bags with a slightly moistened mixture of sand and clay. Lay them flat on the foundation one by one and tamp each course to flatten and compress the "bricks." Add two strands of four-point barbed wire on top of each course to give tensile strength and to help secure the layers together. Lay the next course on top in a running pattern. Hand-tamp the new course and repeat. Completed walls are plastered. Earthen or lime/ sand plasters are preferred and adhere well without preparation. Earthbags provide excellent thermal mass but very little insulation. Readers will notice that a lot of the construction methods mentioned above involve tamping to consolidate the sediment. If a pneumatic tamper isn't available, a makeshift tamper can be as easy as stomping with booted feet. Primitive tampers can be made by screwing a 12-inch-square piece of 1-inch plywood to the end of a 4 x 4 timber, or by drilling a hole into a stump or an 8 x 8-inch hardwood block and driving a 5-foot pipe into it. Cast Earth This type of construction is a proprietary process using a slurry of water, soil, and 10 to 15 percent heated calcium, poured into forms on a concrete foundation. The walls are plastered or finished with stucco for protection and cosmetic appearance. Straw-Clay This material is made from straw and a little clay slip (clay and water used as a binder). Slip is poured into the straw and mixed in until the straw surfaces are slightly wet. The mix is packed into 2-foot-high wooden forms attached to wall framing with lumber or posts. The mixture is then tamped by hand. Bamboo reinforcing is installed by hand, for lateral stability, through holes drilled in framing members along the height of the wall. When a form is filled, a new one is added. After two are filled, the lower is removed for drying. When walls have dried, they are coated with plaster. Straw-clay structures are fireproof, soundproof, and well insulated. Their disadvantage is that they dry very slowly. |
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