Ammonium bifluoride solutions containing two to four ounces of ammonium bifluoride per gallon of water is made up in rubber or plastic buckets and applied to the building surface with a long handled brush. The solution and grime is then removed by steam cleaning. Since ammonium bifluoride may cause etching of clear glass windows, proper precautions should be taken to prevent contact of the ammonium bifluoride solution with clear glass. Should contact occur, the ammonium bifluoride should be washed off as quickly as possible with water.