ABSTRACT
The types of chemical cleaning agent used on buildings involved brush application of alkaline and/or acidic chemicals, followed by water washing. The alkaline cleaning agents used were solutions containing sodium hydro xide; acidic cleaning agents often contain hydrofluoric acid with, or without, the addition of phosphoric acid. The concentrations, dwell times and method of application of these chemicals can vary widely. Due to lack of records, details of the cleaning methods used on the buildings studied here are not known; however, results of chemical analysis indicated that the chemicals used could be broadly identified by the residues left in porous stone.
