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Cleaning (procedures and materials)
The removal of all foreign matter from the stone,
masonry unit and mortar. This is usually the first
phase of a restoration or preservation project. It
will establish the criteria of the colors and
textures to match when repairing the damaged
stones. Sometimes, contractors prefer to do the
cleaning last. However, a mock-up should be
performed first to establish the criteria.
Cleaning is probably the most important phase
and the most misunderstood procedure. More
damage is done during the cleaning operation
than any other phase of restoration. Too often the
cleaning phase is rushed and destructive. Instead
of starting with the gentlest type of cleaning, the
contractor will often start with the most abrasive
type and severely damage the stone. Cleaning
methods should be
only strong enough to do the
required job and no more
.
When using cleaning
products focus on the pH; this is the
concentration of hydrogen ion in a solution. A
small change in the pH value is a large change in
concentration of hydrogen.
Cleaning requires a good knowledge of the
stones. Quartz stones have a greater resistance to
acids and high alkaline detergents. Granite,
which is primarily quartz, will take aggressive
cleaning without damaging the stone; limestone
will not tolerate any cleaning agent because of its
calcium content.
When using detergents, poultices and diluted
acids solutions, watch the pH.