Americans have a fondness for bright, shiny, new things -- cars, pennies and buildings. Show an old building to many Americans and the first thing they will want to do is clean it.
Clean, bright and shiny is not, as Benjamin Franklin would have us believe, always a good thing, at least for buildings. Part of the dirt people sometimes see or think they see is really a patina acquired with age.
But some buildings are dirty, especially city buildings that are covered with the soot, gunk, and grime that settles over a building from the smoke, pollution, and auto exhaust of the 20th century. Getting rid of that accumulation is one of the first things many people try to do when they buy an old house, factory, warehouse, or store.
Cleaning an old building is not always bad, but the methods used can be disastrous. Sandblasting is a particularly destructive process and has long been a bugaboo for people who are concerned with the preservation of old buildings.
It is not the sand that is the primary culprit. The destructive feature of the process is that the sand is blown against the building at high pressure to abrade or rub the dirt away. The problem is that the process takes part of the building away with the dirt.
Sand is not the only material used in abrasive cleaning. Various firms use such things as ground corncobs or coconut shells, crushed walnut or almond shells, rice husks, glass beads, silica flour or water.
The material is blasted at high pressure against the surface. Wire brushes, rotary wheels and power sanders produce the same type of damage.
But what do you use if you want to clean a building? The Interior Secretary's standards for historic preservation projects require that surface cleaning be done with "the gentlest means possible." Those standards are used by the staff of Interior's Heritage Conservation and Recreation Service to determine whether a project qualifies for the special historic preservation tax incentives available for commercial projects.
Projects have been denied approval because they used sandblasting or other destructive techniques that damaged historic buildings. It has become an expensive process for many developers.
For a brick building that has been painted, the gentlest means possible would be to wash the surface with soap, water and a stiff brush, and then to repaint. Many 19th century buildings were painted as soon as they were built to protect poor-quality brick or to imitate stone.
Others were painted or stuccoed to hide alterations or to solve a moisture problem. Blasting away the old paint can mean opening the old, soft brick to possible weather damage, or giving that old moisture problem another place to start.
There are commercial cleaning products that can be used to remove dirt, stains or paint from brick or stone. They are used in combination with water or steam and a scrub brush.
Whatever the method you choose, test it on a small area first and watch the results.
There are two publications that can help you with the job of cleaning your old building. "Dangers of Abrasive Cleaning to Historic Buildings" and "The Cleaning and Waterproofing of Masonry Buildings" are preservation briefs that are available from the Technical Preservation Service Division, Heritage Conservation and Recreation Service, Department of the Interior, Washington.