Liquid Expulsion technique was used in this study to quantify the transport properties and microstructure of a refractory coating used in the Lost Foam Casting process. The pore size information obtained from the Liquid Expulsion Method is found to be well correlated with the transport properties of the porous coating material. For manufacturing process control, the viscosity of these coating slurries prior to its application on expanded polystyrene foam is often reduced by dilution with water and/or using a dispersant. In this paper, the effects of diluting or dispersing the slurry on the microstructure and transport properties of the dried refractory coatings are evaluated. Results show that the dilution and dispersion have opposing influences on the pore size and transport properties. Adding dispersant was found to reduce the transport properties of the refractory coatings significantly, potentially leading to defects in metal castings. The pore characterization technique developed in this paper is also used to determine the effects of drying methods (oven versus air dry) on the pore size and transport properties. (c) 2006 Springer Science + Business Media, Inc.