The application of Zirconium Silicate (ZrSiO2) as refractory coating material can improve the smoothness of casting surface and overcome die soldering. The cost is quite expensive, causing the need for alternative materials to reduce production costs. Alumina (Al2O3) is one of alternative material because of its high melting temperature and free of iron content. This study aims to determine proper concentration variation, distribution of alumina particles as a partial substitution of the refractory fillers in the casting layer, and drying treatment of coating samples. The variation of concentration used in alumina is 16 wt.%, 18 wt.%, and 20 wt.%. Particle distribution used is filler material that is with and without milling. Coating samples optimized by drying at room temperature and 100 °C. The characterization used was Particle Size Analyzer (PSA), viscosity value, and Differential Thermal Analysis (DTA) to test the heat resistance of the coating. The surface scanned by Scanning Electron Microscope (SEM). The results of 16 wt.% concentration alumina in a higher viscosity value facilitates better coating deposition, a wider distribution of alumina particles are resulting a variety of particle sizes that support the quality of the casting coating due to grain interlocking and passing gases out of metal castings, and drying coating samples at temperatures 100 °C produces morphological densities. The result of adding alumina is considered comparable to the refractory coating made from zircon silicate.