Despite technological improvements in its production process, the sanitary ware industry inevitably generates a certain volume of discards, products whose quality is not up to standard. The present paper is the first to scientifically explore clay-based sanitary ware waste (SW) with a view to its valorization as an addition in the design of new, more environmentally friendly cements. The focus is on characterization of the waste and its pozzolanicity, as well as the structural and microstructural changes taking place in the pozzolan/Ca(OH)(2) system in the first 90d of reaction. The findings show that pozzolanicity in clay-based waste is comparable to the activity observed in silica fume (SF) and higher than that found in other clay-based materials and fly ash (FA). The microstructural study of the clay-based waste/Ca(OH)(2) system, in turn, reveals that the proportion of C-S-H gels rises with hydration time. These gels are characterized by long mean chain lengths (MCL) and low Ca/Si ratios. The intrinsic characteristics of this thermally activated clay-based waste qualify it as a type Q pozzolans as defined in the European cement standards, making it apt for use in the manufacture of CEM II, IV, and V cements.