Airlite Hystoriqa Stone is a water-repellent coating which becomes invisible after its application, specially formulated for the protection of mineral building materials. Airlite Hystoriqa Stone is non-toxic, with zero VOC, it stays stable in case of contact with liquid alkaline and acidic solutions and it eliminates the formation of salt deposits whilst maintaining the natural porosity of the substrate. Its formulation is the result of the aqueous dispersion of the water repellent photocatalytic nanoparticles of titanium dioxide. Its innovative formula gives the self-cleaning characteristic against the organic substances with which it comes into contact. The photocatalytic reaction occurs in the presence of sun-light and permits the reduction of air pollution decreasing both the concentration of NOx and SOx.