Water is the main vehicle of pollutants and other decay agents that affect to buildings and monuments. Hydrophobic treatments, available in the market, present significant drawbacks related to their low penetration in building materials, especially in those with low porosity such as concrete, promoting a low durability. Our research group has developed an impregnation treatment specially designed for concrete. Specifically, a sol with low viscosity, containing a silica oligomer, is able to penetrate in the decayed concrete structure producing, in situ, by a spontaneous process, calcium silicate hydrated gel (C-S-H gel), the main component of cement matrix, responsible of its excellent mechanical properties. We demonstrate that the sol can produce new C-S-H by the reaction of the silica precursor with Ca2+ present in the pore solution from the portlandite. We also add to the starting sol two hydrophobic agents: (i) propyltriethoxysilane penetrates into the porous structure and (ii) polydimethylsiloxane produces a superhydrophobic surface. Silica nanoparticles are also added to create a Cassie-Baxter state. The role of each hydrophobic agent to produce hydrophobic and repellence performances was evaluated by modifying their ratio in the sol.