The investigation of dozens of exterior walls on buildings by the authors have revealed that certain sealants used to seal joints in exterior walls have caused the following conditions: 1. Local staining and discoloration of masonry wall substrates due to penetration of sealant into substrates. 2. Local change in absorption of masonry wall substrates due to penetration of sealant into the substrates which results in local discoloration of wall substrates after rains. 3. Surface discoloration of sealant due to dirt accumulation on sealant. 4. Stains in the form of streaks of dirt on masonry and on metal wall substrates due to transfer by rain water of some of the dirt on the sealant surface onto the adjacent surface of the substrate.
Laboratory and field testing of the major commercially available sealants by the authors to date have revealed that silicone sealants have the propensity to stain certain exterior wall substrates while polyurethane sealants do not; that silicone sealants in service discolor more significantly and faster due to dirt accumulation than polyurethane sealants; that sealant that has penetrated into masonry substrates cannot be entirely removed from the substrate by cleaning; and that preconstruction testing of sealants and proper material selection can help to avoid staining of sealant.