Conservation treatments on stone are generally performed on materials that have been exposed for a long time to the action of atmospheric agents, and for this reason, contain variable quantities of soluble salts. Researchers examined a phenol-methyl-polysiloxane resin with low molecular weight, which had been used to treat some samples of Istria stone, Carrara marble, and Vicenza stone by capillary rise and by brushing. The samples were soaked with a saturated solution of MgSO₄ or NaCl before the silicone treatment. The samples were then bathed in water in order to evaluate the efficiency and adhesion of the resin by means of conductivity measurements. It was established that efficiency of the product in these conditions is very low, in fact the salts had been completely washed out. The difficulty of obtaining homogeneous and close films when salt is present is confirmed by scanning electron microscopy (SEM) observations. Some porosimetric measures were performed on the samples and the results are discussed.