This report discusses results of studies on weathering of stoneworks caused by accumulation of soluble salts. Fifteen samples chosen from efflorescence, crust, humidity stains and from parts of the stone which have lost cohesion, mostly from superficial layers of stone from six different monumental stoneworks, representing four types of physico-chemical action, are discussed. In addition to determination of chemical composition pH reactions, content of moisture, microscopic and electron-microscopic examinations, as well as determinations of porosity, specific surface, heat of moisturing and x-ray diffraction, have all been indicated. The typical symptoms of damage and causes of salts accumulation are also described. -- AATA