Plaster from the Cascina Pozzobonelli (Milan), probably built by Bramante in the 15th century, was analyzed to find the raw material composition, the working techniques, and the causes of decay so that conservation work could be carried out. The plasters are of two kinds: decorated graffito and plain, finishing plaster. The graffito consists of two layers, the first with lime, sand, and charcoal, the second with gypsum. The second layer was applied after drying of the first and then engraved while still damp to obtain the graffito. The plain plaster consists of two layers, the first made from lime, sand, and crushed brick, the second made of gypsum. The decay was caused by the high humidity of the environment. The restoration was carried our by sealing the detached areas and consolidating the disintegrated areas with acrylic resin.