Plaster for the walls is essentially the same material as the floor -- a mix of clay-rich earth, sand, water, some chopped straw and a bit of oil. The proportions depend on the binding properties of the clay used. Three coats is a typical application, about 3/4 inch (2 cm) thick, and is applied directly to the cured (thoroughly dried) straw-clay wall.
The chopped straw is omitted from the final coat, which is applied about 1/8 inch (3 mm) thick. Often a potter's clay, and possibly a white sand will be used, for a whiter, more light-reflective surface. Boiled linseed oil, heated, is also added to the final coat to improve spreadability and durability when dry.