In the slip casting process, the relationship between the amount of plaster and water used in the production of molds influences the production of ceramic materials, because the higher the water content in the mixture, the lower the mechanical strength of the mold and higher the water absorption rate. In order to evaluate the influence of the variation in the plaster/water (P/W) ratio in the production of ceramic pieces, plaster molds with P/W ratios of 2.0, 1.67, 1.43, and 1.25 (100 parts of plaster/50, 60, 70, and 80 parts of water by weight) were manufactured and used in the production of ceramic pieces. It was found that the fluidity, density, flexural and compressive strength of the molds decreased with the increase of water content. For pieces sintered at 1050 °C, higher density and lower porosity were observed for ceramic materials obtained with molds with higher plaster/water ratios.