Sodium chloride crystallization in a “salt transporting” restoration plaster

In recent years several types of restoration plasters, especially developed for salt loaded substrates, have been introduced on the market. The behaviour of these plasters in the field is, however, not always satisfactory. The reasons for failures may be found both in the moisture and salt transport behaviour of the substrate/plaster combination and in the severity of the situation (salt load, moisture supply and environmental conditions).In the present paper a restoration plaster for salt loaded substrates is examined. Its properties and composition are investigated in laboratory by means of multiple techniques (MIP, PFM, ESEM, XRD and FTIR). Particular attention is given to the study of the salt (NaCl) crystallization in the plaster. Field situations are considered in which this plaster shows damage after a few years from its application. The knowledge of the specific situation, together with the information gained in the laboratory research on the plaster, explains the fast development of the decay.