This technical report provides information on the careful removal of exterior dirt, paint, stains and graffiti from historic masonry surfaces. It covers all aspects of a cleaning project, including: identifying building materials to be cleaned and adjacent materials which might be affected by cleaning; scheduling cleaning around other preservation or maintenance work, what to ask for in cleaning specifications and what kind of test cleaning procedures ensure a successful project. The report also includes warnings about using certain techniques on specific building materials, as well as possible dangers to people and the building's environment. A useful chart summarizes both cleaners and removal techniques. Bibliography (25 entries), photographs.