Traditional Cleaning Methods:
Traditional Cleaning methods can usually be broken down into 3 categories: Water, Chemical, and Mechanical
Water: A low pressure water wash is often considered “not enough”, and a high-pressure wash or steam cleaning can destroy the brick and mortar while forcing moisture deep into the stone itself. Since brick and stone are porous they may absorb moisture, leading to spalling or cracking. This excess water will also contribute to bringing soluble salts from within the masonry to the surface leading to the formation of efflorescence
Chemical: some types of masonry will dissolve easily with acidic cleaners, even in a diluted form. Some chemicals can change the color of the masonry itself as well as leave a hazy residue despite a heavy rinse. They can react with components of mortar, stone, or brick to create soluble salts and eventually lead to efflorescence. Historic Brick buildings are particularly susceptible to damage from hydrochloric (muriatic) acid.
Mechanical Cleaning: Abrasive blasting, hand tools, grinders, sanding discs, wire brushes, etc. all abrade the contaminants off the surface with damaging results. Brick is a fired product and is hardest on the outside where temperatures were the highest; damaging this protective layer will expose the softer brick to accelerated environmental deterioration. Therefore, mechanical cleaning should not be used, especially on mortar joints using limestone.