Aim of the present invention is to obtain cementitious products having smooth, planar surfaces and low thickness for applications having aesthetic purpose, of integrated architecture or as substrates, for example for a thin-film photovoltaic unit, with controlled curling and surface roughness, manufactured by mold casting of a fluid composition comprising: I. a hydraulic binder; II. one or more aggregates; III. an anti-shrinkage agent; IV. a superplasticizer agent; V. water, wherein the percentage by weight of said hydraulic binder in the composition is lower than that of said aggregates, and wherein said aggregates have a maximum diameter dmax not greater than one third of the thickness of the product, the final product thus having an arithmetic mean surface roughness Ra not greater than 500 nm and curling not greater than 1500 micron.