MASONRY CLEANING
Masonry cleaning shall be undertaken by the most gentle means possible. Most buildings in the East Row Historic District have never been painted and display their original brick and stone surfaces. Over time these masonry surfaces have weathered creating a richness of textures and colors which provides distinction and individuality to buildings. In most cases cleaning of brick and/or stone surfaces may not be warranted. However, if cleaning is desired the following methods are available:
- Water and Detergents -- This cleaning method is the least harmful to brick and stone surfaces and is relatively inexpensive. This cleaning can be performed by a non-professional although care must be taken not to soak the brick too extensively. For most buildings in the East Row area this cleaning method would be sufficient. Low pressure water cleaning is acceptable as long as the pressure is low to moderate, such as 30 - 60 pounds per square inch (psi). Water cleaning above this psi can damage the masonry and mortar and is not acceptable. A garden hose spray nozzle operates around 30-60 psi. It is best to begin at that pressure and gradually increase the pressure until it is effective, but remaining below 80 psi. Additionally, a pressure gauge mounted on the nozzle is more accurate than one mounted on the compressor.
- Steam Cleaning -- This is also a good method for cleaning masonry but is more expensive and the machinery must be operated by a professional. This is a recommended and acceptable cleaning method for buildings in the East Row Historic District.
- Chemical Cleaning -- The use of chemicals to remove paint on brick or masonry surfaces has been popular in recent years and can be an effective cleaning method. This process can be costly and professionals must be used who are experienced with this cleaning method and will not etch or scar the masonry surface. The repainting of brick or masonry surfaces rather than removal by chemicals should be considered.
Chemical cleaners do have problems which may include:
- A change in the color of the masonry caused by the chemicals, not by the removal of dirt
- They may leave a hazy residue in spite of heavy rinsing
- Chemicals can react with components of mortar, stone or brick to create soluble salts which can form efflorescence
- Historic brick buildings are particularly susceptible to damage from hydrochloric (muratic) acid
Effects of sandblasting on brick surfaces.
- Abrasive Methods: Sandblasting/Abrasive Blasting/High Pressure Water -- None of these methods are acceptable alternatives for masonry cleaning. Abrasive cleaning is destructive and causes irreversible harm to the historic building fabric. Abrasive methods remove the hard, outer protective surface of brick making it more susceptible to rapid weathering and deterioration. Additionally, abrasive methods can erode the bond between the mortar and the brick and also can remove portions of the mortar, requiring expensive repointing and masonry repair.
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