 What is applied depends on the location of the wall; if it is located in an area where it will be exposed to water (such as in a bathroom or utility room) it will need to be coated with a concrete layer.If it is located in a living room or bedroom, it can be covered with adobe plaster.A tin can wall that has half of its structure outside (such as the wall of an entrance to a building) will be coated with cement on the outside and adobe on the inside.