Case Study: This picture shows extensive damage from leaking skylight flashing resulting in spalling of brick. Even with all the obvious water penetration, little to no staining is evident.
Detail of spalled area
Close up of the spalled brick showing deposits in brick which are the source of staining. These deposits exposed to air and weather consistently have no staining around them.
Area of brick showing staining under a sound roof. The water that caused this staining migrated slowly internally to a dry area and left the stains on the surface upon drying.
Our Conclusion: Water saturation and migration to a dry area is the consistent cause of these types of stains, not the brick and not our chemistry...