The construction of Riga Dome Cathedral was initiated in 1211, at the same time the Capithulum hall of Cathedral was built. In order to diminish the problems caused by moisture, during the last restoration (already in 1888-1891) the walls of Capithulum hall were covered with damp proof sandwich-type plaster, consisting of cement – glass tile (ca 4-5 mm thick) – cement. Thus the evaporation of water through the walls is hindered. Soluble salts crystallise on the surface of carvings dislocated above the level of historical hydroisolation and cause damages. The processes of corrosion of historical building materials of Capithulum hall were studied from the viewpoint of moisture and salt migration.The type, range and distribution of salts and moisture in masonry of Capithulum hall were detected by qualitative and quantitative chemical analysis, measurement of physical properties and XRD analysis.