Q1: Why does magnesium fluorosilicate have a hardening effect on concrete?

Magnesium fluorosilicate reacts with free calcium hydroxide in concrete to form insoluble calcium fluoride and silica gel, filling the pores in the concrete and thus increasing surface hardness and wear resistance. It also prevents weathering and white spots on the concrete surface.

Q2: What is the solubility of magnesium fluorosilicate? How should the solution be prepared for use?

Magnesium fluorosilicate hexahydrate has high water solubility, approximately 648 g/L at room temperature. A 1% aqueous solution has a pH of approximately 3.1, which is acidic. In industrial use, a 10%–20% aqueous solution is usually prepared before spraying or brushing onto the concrete surface. When preparing the solution, magnesium fluorosilicate should be added to the water slowly with continuous stirring to avoid localized overheating. The solution should be prepared and used immediately and should not be stored for long periods.

Q3: What reaction occurs between magnesium fluorosilicate and calcium hydroxide in concrete?

Magnesium fluorosilicate reacts with calcium hydroxide, a cement hydration product, to form silica gel and calcium fluoride, which fill the microporous structure of concrete, thereby improving surface density, wear resistance, and weathering resistance. Simultaneously, this reaction eliminates efflorescence (white bloom) on the concrete surface, making the building more aesthetically pleasing.