The effects on the slurry rheology of the chemical composition of suspensions representative of those typically adopted for the washcoating of structured supports have been studied in this work, with the purpose of rationalizing the process conditions used in the preparation of structured catalysts. It has been found that the viscosity of the suspensions can be easily predicted and controlled by knowing the pore volume and the nature of the surface of the dispersed powders. In order to prepare suspensions, containing different powders, with the same rheology, water content has to be modulated considering the pore volume, while the dispersant (nitric acid) amount has to be proportional to the quantity required by the complete charging of the surface of the dispersed powders. Obtained results clarify some fundamentals of the washcoating processes and allow a dramatic reduction of the number of experimental tests typically performed to washcoat a structured support starting from a new catalytic material.