The organic derivatives of silicon have interesting characteristics owing to their organomineral nature and to the bond between Si-O that is reminiscent of the quartz configuration. The author describes the results obtained with silicon resins, silicate esters and silicon rubber. The first ones (silicon resins) are applied solely as waterproof masonry as well as other waterproof building materials; they have the advantage of not blocking the pores of the material impregnated, but instead, of forming a sort of colorless, almost invisible facing that prevents water capillary aspiration, while permitting vapor to pass. The siliconates and the silicate esters are used as consolidation agents; they restore cohesion to disintegrating (or crumbling) stone by the formation of polymeric structures reticulated and of SiO₂. The silicon rubbers are used, on the other hand, for the manufacturing of joints capable of expanding and contracting and of pliable molds for the reproduction of architectural elements. G.G.A. (A.A) -- AATA