Sensitive measurements of interaction between sulphur dioxide and treated/untreated stones were performed by the method of stone surface labelling by radioactive isotope 85 kr. After a few hours, these measurements made it possible to detect even a slight formation of calcium sulphate after reaction with low concentrations of so2. This study reports direct application to marbles, to test the conservation efficiency of materials used for surface protection. Two types of marble (Carrara and Bohemian marble from Slivenec) were impregnated with methylmethoxysilanes, ethylethoxysilanes, and Fomblin p1-10.