Clay
Clay is often found in subsoil, and it can be excavated locally using a spade or digging machine. (If local sourcing isn’t possible, purchase clay from a pottery supply store or quarry.) Clay is usually golden yellow, orange or brown, but it can also be gray, purple and green. It’s sticky and clumps together when wet. (Read Building with Cob for more information on clay subsoil selection.)
Lime
Lime is produced when calcium carbonate (most often in the form of limestone or chalk) is burned, then mixed with sand to make a mortar/plaster.
Casein
Casein, a milk protein, is used to make milk paint or as a paint and plaster additive to assist with adhesion and dust prevention.
Rock dusts
You can add natural sands and marble dusts to plasters and paints to provide bulk and structure. Purchase them from building supply stores or directly from quarries.
Natural earth pigments
By grinding up rock or earth, we obtain naturally occurring pigments such as ochres, siennas, umbers and oxides. Purchase them from specialist building supply stores or artist supply stores.
Beeswax or carnauba wax
Natural waxes provide polish and sheen and help protect finishes such as earth plaster. Most beekeepers sell beeswax directly to customers.
