The casein primer is composed of milk protein.

The primer is applied prior to the application of a paint or a plaster. A transparent primer, it is used to stabilize backgrounds and uniformize the absorption of surfaces to ensure the proper rendering and durability of the chosen finish. It is applied on untreated substrates such as plaster (lime, plaster, cement or clay), plasterboard, plaster, limestone and concrete. It is not suitable for smooth, non-absorbent or permanently damp substrates. It can, in certain cases, be used to consolidate interior coatings (clay coating for example).

Packaged in powder form, it can be diluted with water and applied easily with a brush in transparent base coats.