Start with a foundation, mix the cob, build up walls and then cover with plaster to seal the structure. Cob structures are made with natural substances, and some houses in Europe have lasted hundreds of years using the mixture.
- Lay out the foundation
Dig a trench around the perimeter for the building's foundation. Lay gravel down on the trench and then cover gravel with stones or reclaimed concrete chunks. Dig the trench in such a way that water runs away from the foundation to protect the cob walls when it rains.
- Mix the cob
Take two parts clay, four parts sand and one part straw and mix them together. Put clay in water overnight so it turns into the consistency of pudding. Put one part sand down on a tarp, then one part clay, followed by another part sand. Mix these substances together, adding two more parts sand during the process. Place straw on top of the clay-sand mixture and keep turning the substance over until the straw is evenly distributed.
- Sculpt and build
Place one clump of cob on the outside edge of the wall, one on the inside and then one in the middle. Mash these three cobs together. Repeat this process until the structure is complete, working upwards, sideways and around corners. Knead clumps of cob together by working straw fibers into surrounding material. Plaster the outside to seal the structure and keep out the elements.