Anyone faced with the task of performing restorative cleaning on a historic building has a whole series of fundamental and far-reaching decisions to make. The unique testimonies of the past must not be irretrievably damaged or even destroyed by inappropriate methods, as facade cleaning is one of the most demanding cleaning tasks. There is hardly any other cleaning task that requires so much know-how and experience or the use of a range of technical procedures and equipment. The diversity of materials used in building facades, the state of decay caused by weathering, the varied structures & shapes and the numerous types of contamination found on the exteriors of buildings, always necessitate a solution which is specifically designed to suit the conditions on site. A distinction is made between mineral soiling such as efflorescence, sintering, pigment discolouration and the products of corrosion, i.e. verdigris, manganese dioxide and rust and organic soiling,i.e. soot, algae, moss,lichen and bird droppings. Dirt containing oil and grease adheres to smooth surfaces and provides a good base for further deposits.