Design of ceramic tiles with high solar reflectance through the development of a functional engobe

Roofing solutions with high capacity to reflect incident solar radiation, the so-called cool roofs, can provide an effective answer to summer overheating of either individual buildings or whole urban areas. Nowadays, commercial cool roof products are mainly represented by organic membranes and coatings, but ceramic tiles can offer an interesting alternative or complement in view of their high durability. This work presents the procedure through which a traditional white engobe and a glazed tile with high solar reflectance are developed by the introduction of suitable raw materials and pigments, in the perspective of production by commonly used industrial processes. The solar performance was checked for both light and dark supports and for different engobe thicknesses up to 250 μm; the estimated solar reflectance values were correlated with surface properties such as microstructure, mineralogical composition, and roughness. The best performing engobe, applied as a 200 μm layer, improved solar reflectance of the sample up to 0.90. Three different glazes were then applied on engobed samples and were found to slightly affect the reflectance and improve the resistance to mechanical stress or weathering. A white gloss glaze was found to be the best performing one in terms of solar reflectance.