Characterization of a hybrid nano-silica waterborne polyurethane coating for clay bricks

A transparent hybrid organic–inorganic waterborne coating was evaluated for the protection of clay bricks. The nanocomposite film was prepared by combining an environmentally friendly process based on UV-curing of water-based acrylic resins and a mild thermal treatment to form nanosilica in situ from alkoxysilane precursors. Coated and uncoated facing bricks were compared by scanning electron microscopy, surface profilometry, water wettability, and capillary rise tests. The hybrid coatings act as a moderate water repellent; interestingly, no appreciable alteration of the aesthetic properties of the brick was observed, in particular no gloss or color change appeared after the treatment.