Perfluoropolyethers, having molecular weight from 600 to 7000, have been tested as water repellents to be applied on stone. They are in fact colorless, chemically stable, permeable to oxygen, nitrogen and water vapor, insoluble in water and common organic solvents but soluble in fluorocarbons, thus providing a reversible treatment. When sprayed on the surface of the stone, perfluoropolyethers having molecular weight 6000-7000 have provided the best results by reducing the water penetration by two thirds. -- AATA