Conservation of earthen constructions: Earth-gypsum plasters

Earthen constructions represent an interesting and important architectural heritage, whose conservation is necessary in order to make possible the transmission of a technological culture which keeps values of the uniqueness of the landscape as well as of its history. Observing many unplastered earthen buildings and their weakness towards the external surroundings conditions, it seemed fundamental to set-up and test out treatments for the protection of the walls of such kind of buildings, with the aim to improve their resistance against the aggressive action of external agents and in particularly, of the water. The preservation of this heritage calls for the definition of effective techniques able to mitigate and, if possible, to prevent processes of alteration and ruin, ensuring a long-term conservation. In order to do so, activities designed to assess the effectiveness of different surface protection methods have been carried out, aiming to prevent the arising of defects. The application of plasters on earthen constructions, even if makes it difficult to appreciate their real material consistence, can guarantee their adequate safeguard. Used since ancient times, it certainly is the protection method more diffused worldwide. A testing campaign was conducted on different plasters prepared mixing earth and gypsum (the so-called plaster of Paris) or earth, gypsum and additives, real sacrifice surfaces which, trying to guarantee the readability of the actual aspect of the walls, intend to offer an effective way of protection against the atmospheric agents characterizing the environment in which the constructions are located. The testing campaign, including chemical and mineralogical characterization (XRD and FTIR), colour evaluation (spectrophotometry) and performance tests as capillary absorption, erosion spray tests and Geelong tests made it possible to assess effectiveness and performances of the different plasters.