1. Clay plasters are designed for internal use but can be used externally if protected from water. They should not be used as an external wall finish exposed to rain. 2. Tools for applying clay plaster include hawks, trowels, sprayers, buckets, and masks. Walls should be moistened before application depending on material and weather. 3. Clay plaster is mixed by adding dry powder to water in increments and mixing until it reaches a mousse-like consistency. It is applied in one or two thin coats, smoothed after setting, and can be finished with hard troweling, sponging, or glazing.