Materials on the basis of the magnesian binding substances possess a number of positive characteristics that increases interest in them. Their main shortcoming is low water resistance. Due to input of natural mineral additive of hongurin, the water resistance of a magnesian stone increases. The influence of this additive on the main properties magnesian binding and a stone on its basis is considered in this article. Optimum concentration of a grouting fluid – magnesium chloride solution is also defined. It is defined that input of a natural hongurin to structure of magnesian binding promotes formation of a dense, strong and waterproof magnesian stone.