Silica sol physico-chemical parameters mainly include: the content of SiO2, density, content of Na2O, PH, kinematic viscosity, colloid particle diameter, etc., the physical and chemical parameters of the main affects the stability of shell strength, coating and coating powder liquid ratio.As the general precision casting enterprise hard to these physical and chemical parameters for testing, so, on the one hand, we must strengthen the supplier selection, evaluation and validation, on the other hand, the surface layer and back layer should choose to use different specifications of the silicon sol, such as the surface of S - 830 silicon sol choice, choice of S - 1430 silicon sol back layer.