Masonry Magazine March 1971 Page. 24
Sandblasting involves projecting an abrasive material, such as sand, through an air hose and nozzle by compressed air at various pressures, depending upon the surface to be cleaned and the type of unit involved. This method should be employed only when the units will not be damaged and/or when certain types cannot be successfully cleaned with high-pressure steam. This sometimes is the case with respect to more porous material, such as limestone, sandstone and certain types of brick; but, regardless of the type of unit in the building to be sandblasted, a sample of substantial size should be done by the contractor before proceeding with the entire job.
Hand Washing
Many buildings of smaller size have been cleaned successfully by hand washing. It is a bit slower and does not give the added advantage of the heat in high pressure steam. Usually this work is done by using some sort of soap or detergent with cold water. The method is more costly because it is slower, does not lend itself to a job of any size, and must be done more often.
High-Pressure Cold Water
Reasonably new in the field, high-pressure cold water blast is being used a great deal in the Midwest and Pacific Coast regions but not much in the East or large eastern cities. It does a very satisfactory job; however, getting rid of the large volume of water used is sometimes a problem. Another requisite of this method is an ample water supply.
Chemicals and Steam
Mr. Newman points out that chemicals and high-pressure steam are used primarily to remove applied coatings to masonry, such as paint. This is a highly specialized field and frequently the proper cleaning agent can be determined only after an analysis of the various factors involved in a particular project.
The following cleaning methods are described in literature of the Western Waterproofing Co., Inc., St. Louis, Missouri.
Wet Sand Cleaning
This method is used on unpolished granite, hard brick, rock face or rough finished limestone. This type of cleaning depends on a water-cushioned abrasive action for its effectiveness. It is recommended for removal of paint or other surface coatings, or in other situations where abrasion of the surface is permissible. Wet sand cleaning employs water in the cleaning action to eliminate dust.
Wet Aggregate Cleaning
This is a special process developed by Western for use on limestone, soft brick or sandstone, particularly effective on surfaces with flutings, carvings and other ornamentation. It is a gentle but thorough process, employing a mixture of water and a friable aggregate free from silica, delivered at low pressure through a special nozzle with a "scouring" action which cleans effectively without damage to the surface.