Physical Method: Primarily involves using external force to push dirt away from the building's exterior walls. The specific method is to wash with water (or spray water) to soften, peel off, and melt the dirt, followed by a thorough rinse. This method is mainly used for removing dust, floating debris, and sand residue from exterior materials like glazed tiles, washed stone, and mosaic, but it consumes a significant amount of water. Additionally, high-pressure spraying can easily damage the exterior walls and is ineffective against bloodstains and heavy dirt on some walls. Relying solely on this method is not practical.

Chemical Cleaning Method: The chemical cleaning method involves dissolving, separating, and degrading dirt using chemical reagents to achieve the purposes of descaling, rust removal, degreasing, and defatting. There are three types of exterior cleaning agents: neutral, alkaline, and acidic cleaners. However, the neutral cleaner is the primary choice. The main components of neutral cleaners include surfactants, detergents, and additives. In fact, they are not truly neutral but are slightly alkaline or acidic. Nonetheless, they are commonly referred to as neutral cleaners. They possess wetting and emulsifying properties, along with various functions such as dispersion and solubilization.

Corrosive acid wash agents like hydrochloric acid and hydrofluoric acid are a double-edged sword. They can remove dirt but also damage the base material, reducing its strength and surface finish. Moreover, hydrofluoric acid is toxic to humans. Therefore, according to the cleaning standards both domestically and internationally, it is important to select the appropriate exterior washing agent. Additionally, the exterior surface should be rinsed or sprayed with water before cleaning to reduce the amount of cleaning solvent used and enhance its effectiveness.

Chemical cleaning methods are primarily characterized by their suitability for cleaning various types of exterior wall soiling, with fast and effective results. Generally, as long as the cleaning agent is chosen properly, the cleaning will be very thorough. However, chemical agents are corrosive and some can impact the environment. Therefore, construction companies and operators should also select appropriate cleaning agents and eco-friendly products.