ABSTRACT
The decay of a rock exposed to the weathering is a phenomenon that normally occurs on the Earth’s surface. This decay also affects the stone used for building, creating serious problems for construction. Different decay phenomena related to the petrographical characters of the Lombard stones are described according to their effect on the stone surface: i) without worsening; ii) loss of material from the surface; iii) loss of outward form; iv) deposit and/or formation of by-products and v) loss of mechanical properties. The scientific knowledge of the decay phenomena is the base of the preservation methods of stones used in architecture.
