Organosilicon compounds have been used with good results for the surface protection of porous building materials. The paper attempts to use silicon-based admixtures for volumetric hydrophobization of cement mortar and paste. Basic research was carried out to determine the effect of two organosilicon admixtures: based on poly (dimethylsiloxane) and an aqueous solution of a methyl silicone resin. The paper presents the results of research on the influence of siloxanes on the compressive strength, water absorption and microstructure of cement mortar and the wetting angle of cement paste. The effect of poly(dimethylsiloxane) to reduce water absorption is particularly advantageous. But its negative impact on the mechanical properties must be solved. The use the water solution of methyl silicone resin as hydrophobic admixtures to bulk treatment requires further research taking into account the long-term studies.