Top-spray fluidised bed coating scale-up experiments have been performed in three scales in order to test and validate the Akkermans flux number as possible scale-up parameter. Coating operations were performed on low porosity sodium sulphate cores View the MathML source coated with aqueous solutions of Na2SO4 using Dextrin as binder in three top-spray fluidised bed scales, i.e. a small-scale (type: GEA Aeromatic-Fielder Strea-1), medium-scale (type: Niro MP-1) and large-scale (type: GEA MP-2/3)