One is that the silica particles gather and grow, and then precipitate. The other is that the silanol groups of the silica particles contained in the silica sol dehydrate, and the siloxanes are connected to form a gel with a network structure. Another point needs to be pointed out: the silica sol freezes below 0°C, at which time the silica particles precipitate and gelation occurs, but the binder function has been lost at this time. One thing to explain here involves the storage of the silica sol. It must be ensured that it cannot be exposed to the sun or frozen. Exposure to the sun may cause the silica sol to lose water, increase the silica content, and cause gelation; while freezing will cause the silica particles to aggregate and precipitate. Therefore, the silica sol must be sealed and stored at room temperature. The silica sol uses the second gelation method as a binder. In the gelation process of the silica sol, the colloidal particles form a capillary network structure with hydrogen bonds in the early stage of drying; the later stage of drying is mainly the dehydration of the silanol groups to form siloxanes, which are connected to form a spatial network structure.