Binary-sized particle slurries (binary slurries) prepared by mixing micro-particles and electrostatically stabilized nano-particle slurries (nano-slurries) were cast onto metal substrates to form wet coatings and the drying process was studied. The highly charged nano-particles were found to deposit on the surface of the micro-particles, resulting in a decrease in the viscosity of the binary slurry. The drying kinetics were classified as an initial constant rate period (CRP), followed by a falling rate period. In the early stage of CRP, the movement of micro-particles induced coating shrinkage and tensile stresses developed due to the constraint of the substrate. Thereafter, the nano-slurry continued to dry and shrink around the static micro-particles without further coating shrinkage, but with an increase in the stress. The addition of micro-particles reduced the level of the maximum stress and prevented crack formation during drying. The microstructure of green coatings shows the presence of nano-particles between micro-particles that cement the micro-particles together.