Silica sol mainly consists of silicon dioxide, high-density substances, sodium dioxide, substances that adjust acidity and alkalinity, rheological agents, colloidal particles, etc. The physicochemical parameters of these substances primarily affect the strength of precision casting shells and the stability of coatings.

Since precision casting manufacturers find it difficult to detect these physical and chemical parameters, on one hand, the selection, evaluation, and confirmation of suppliers should be strengthened. On the other hand, different specifications of silica sol should be used for the surface and the back; S-830 type silica sol is selected for the surface, and S-1430 type silica sol for the back. In precision casting production, the preparation method of the coating directly affects the quality of the castings.

The preparation of the coating usually starts with adding silica sol, then a wetting agent, followed by refractory powder during mixing, and finally a defoamer. To ensure coating quality, the surface coating always uses new materials, and the stirring time should exceed 24 hours before use; for some newly prepared mixtures, the stirring time can be shortened to 12 hours. The mixing time for the transition and back layers can be less than that of the surface coating; all use newly prepared paint with stirring time exceeding 12 hours, and for some newly prepared coatings, the mixing and stirring time can be reduced by more than half. If the prepared paint is not used, it should be sealed with a cap to prevent moisture evaporation.