Masonry Cleaning

"A well-planned cleaning project is an essential step in preserving, rehabilitating or restoring a historic masonry building. Proper cleaning methods and coating treatments, when determined necessary for the preservation of the traditional masonry, can enhance the aesthetic character as well as the structural stability of a historic building. Removing years of accumulated dirt, pollutant crusts, stains, graffiti or paint, if done with appropriate caution, can extend the life and longevity of the historic resource." — Preservation Briefs #01, Technical Preservation Series, National Park Service, US Dept of the Interior:  "Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings," Robert C. Mack, FAIA, and Anne Grimmer.