Abstract: The effects of additive in the silicasol back coating slurry on the weight of investment castings are investigated. The results reveal that the additive has strong impact on the weight of the castings and when the content of the additive is 6.0% of the silicasol in weight, the weight of the castings has an optimum concentrated distribution and the problem of overweight and underweight in the production of the castings is solved.