Once the insulation dried, the wall were ready for the base plaster. The ratio of clay, sand, and chopped straw is 1:3:1 respectively. Water to taste. Remember,to test your soil first to figure how much clay or sand to add to it. At Aprovecho we have been working with an almost pure red clay and have done several test patches to develop the given ratio. We mixed using tarps and good ol’ fashion foot stomping. The base layer is different from the finish layer because it can first be applied with hands to get good adhesion and then smoothed and evened with a wooden float.