Spin-coated cellulose thin films have been used as model substrates to investigate the crystallization of calcium sulfate dihydrate (gypsum) under industrially relevant conditions using highly concentrated dispersions of calcium sulfate hemihydrate (bassanite). Pre-treatment of the films by regeneration in aqueous solutions of Ca2+ promotes gypsum crystallization specifically on the polysaccharide substrate in the presence of bassanite or in control solutions comprising supersaturated calcium sulphate. The results demonstrate a facile procedure in which inert films of cellulose are rendered active with regard to gypsum nucleation and growth, and could have important applications in the processing and general application of Plaster of Paris-based materials and products.