Cementitious waterproofing is a polymer-modified cement coating applied to the surface of concrete to fill pores and reduce permeability — it relies on a continuous physical barrier and is vulnerable to cracking if the substrate moves. Crystalline waterproofing uses reactive chemicals (typically cement, quartz, and active silicates) that penetrate the concrete matrix and form insoluble crystals inside the capillary pores, permanently blocking water migration even under hydrostatic pressure. Crystalline systems are self-sealing to minor cracks and remain effective even if the surface is damaged, making them the preferred choice for water-retaining structures such as tanks, reservoirs, and basement walls.