The influence of material characteristics and environmental circumstances on the efficiency of water repellent treatments of historic facades

Water repellents are widely applied directly to the outer surfaces of existing buildings to increase the hydrophobicity of porous materials. Research on the efficiency of water repellent treatment under practical approaches and environmental circumstances are limited. This study aims to examine the hydrophobic efficiency of a siloxane-based water repellent solvent on different materials (natural stone, brick and lime mortar) using the practical application approach of spraying, and to determine how material characteristics and application conditions affect the water repellent agent’s efficiency. Spray-treated samples demonstrate comparable hydrophobic efficiency to those capillary absorbed samples, though absorb less active agent during treatment. Application temperature and relative humidity have little effect on water repellent efficiency. Moreover, the critical coverage amount for different material varied. Lime mortar and limestone's hydrophobic performance is less effective than that on brick and sandstone due to their chemical components and pore structure.