The deterioration of bricks results from the independent operation of several mechanisms: hydrolytic reactions, hydration reactions, exchange processes and mass transport phenomena. These processes generate a micro-porous network within the brick as well as a layered system of micro-cracks parallel to the exposed surface. For the stabilization and preservation of old bricks in situ, it is necessary to select an impregnant which is compatible with the mineral constituents lining the pores of the stone, and to get this material to penetrate into the subsurface micropores. The substances that have been employed to date are primarily organic polymeric compounds, including silicones.