Exterior Building Cleaning
General. The purpose of this section is to give the Specifying Authority the basic information to prepare a specification for the cleaning of exterior building stone.
Exterior building stone is considered in this section to be all stone used on the exterior of a structure, either as a structural component or as a facing material, with the exception of polished, finished marble. Even though polished marble is not recommended for exterior use, it is occasionally used on storefronts, column facings, and similar treatments.
Regular Cleaning. The ideal in maintaining exterior building stone is to clean it at periodic intervals (at least annually, depending on atmospheric conditions) by simply hosing down with clean water. This will prevent accumulation of dirt and impurities.
Sporadic Cleaning. If cleaning the stone is not done regularly, one of the water systems (hydraulic, hydro-air, plain water) will be the most effective method at the lowest cost.
Dirt on Older Buildings. Where dirt has accumulated on older structures over a long period of time, a combination of methods may have to be employed to properly clean the stone. Plain water jet is satisfactory for removing most accumulation. No chemicals should be used which would be injurious to the stone.
Brushes may be necessary for the removal of certain surface impurities. Soft fiber brushes are recommended.
Test Panels. By cleaning and inspecting test panels, the Specifying Authority can determine if the method is satisfactory. This procedure eliminates the possibility of improper cleaning; since the Owner and Specifying Authority can see what results will be obtained prior to commencement of the total contract. It also gives the Cleaning Contractor a standard to work toward, making definition of the cleaning more specific for all parties concerned.
Source: Marble Institute of America – Cleaning and Maintenance