Résumé On peut définir la «maladie de la pierre» comme une accélération de l'altération naturelle des surfaces des pierres sous l'action de l'environment. Cette accélération paraît être due essentiellement à la pollution atmosphérique, tandis que les autres facteurs climatiques (gel, oscillations thermiques, agents biologiques etc.) modifient les symptômes et la vitesse de l'altération. La défense contre l'altération est basée sur les traitements de nettoyage, consolidation et protection qui ne. peuvent quand même pas produire de résultats permanents, si les pierres restent exposées à un environnement agressif. Le succès de la conservation dépend alors de l'établissement de routines d'entretien très soignées et de la continuation des études visant à évaluer et à améliorer la performance des matériaux employés.

Summary Stone deterioration is a natural process caused by the action of the environment on stone surfaces. The number of factors involved is large (frost, thermal shock, wind, biological agents, crystallization of soluble salts, etc.), and it, is quite difficult to assess their relative importance. The stone of monuments exposed to urban atmospheres in continental areas of the temperature region undergoes an accelerated deterioration process, frequently called the “stone disease”. The assumption is made in this paper that the main cause of this process is condensation of humidity in the presence of air pollution; climatic factors (such as frost, thermal shock, etc.), would influence the process affecting both, the symptoms and the rate of decay. Conservation practices include cleaning (aiming to remove soluble salts and other dangerous materials from the stone surface) and consolidation by means of inorganic reactions (silicates, fluosilicates, baryta) or organic synthetic polymers (silicones epoxy resins and others). Protection of threatened stone objects may be achieved through removal from external exposure or application of protective screens in winter, when the deterioration factors are more active. Application of film forming materials may be successful if the base material is clean and coherent but this is dangerous on weathered surfaces. Anyway all treatments must be considered as temporary measures and subjected to periodical inspection and renewal if the stone is exposed to an aggressive atmosphere. An improvement of the present conditions of the conservation of stone monuments may be hoped only if continuous maintenance schedules are established while conservation processes are being tested both in the laboratory and in the field.