Stone is a widely favored material for building façades due to its durability and aesthetic appeal. It is often used in the exterior curtain walls of malls, hotels, and high-end residences. However, in humid climates—especially during the rainy season—stone surfaces are prone to retaining moisture due to their porous structure, making them ideal breeding grounds for moss and mildew. These biological stains not only compromise the appearance of buildings but may also lead to material deterioration and discoloration over time, requiring regular maintenance and cleaning.