Masonry Magazine August 2001 Page. 12
RESTORATION
CLEANING
OF MASONRY
COVER STORY
by James Diedrich and Larry Kotke
The restoration of old buildings utilizing the chemical process has been around for more than fifty years. But, at the same time, it seems to be a well-kept, elusive secret. There are still architects and contractors out there that think the only way to clean an old dirty building is to sandblast it or "just use some muriatic acid on it." The problem with muriatic acid is that it has such inconsistent purity; muriatic acid should never be used to remove pollution grime because it is not effective for this process.
Then there are some people that won't clean a building because it loses its "character." That argument may have some merit in old Europe but, on American buildings, dirt hardly constitutes antiquity.
There are many reasons for cleaning and restoring old buildings. No one would consider changing a few areas of color on an old master's painting. Why, then, should it be acceptable to allow pollution-grime on a building to alter the subtle color relationships designed to be a permanent part of an architect's composition?
No one seems to object to removing films of dirt from old paintings, but it is not uncommon to hear preservationists complaining about the loss of a "venerable patina." If only the architect, who carefully selected design features, colors and textures of his composition, could argue with these well-intentioned but misguided activists! Accumulated grime hides not only colors, but subtle molding profiles, delicate carvings and textural differences between materials.
There are, however, more than aesthetic reasons for cleaning:
PREVENTIVE
Dirt layered on exposed surfaces aids in the retention of water. Both chemical and mechanical deterioration are encouraged by this additional moisture:
a. Freeze-thaw - Damage is increased in proportion to the quantity of retained water.