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 Figure 4-11. Sources of Water Damage Around Chimneys.
Note entry points at chimney cap, parapet, flashing, and
defective mortar joints.
(Source: Respectful Rehabilitation: Mason ry, The Preservation
Press, National Trust for Historic Preservation)
Before attempting any type of cleaning, it is important to
find out what kinds of dirt are present, determine whether the
dirt is actually damaging the building, and decide on the
gentlest possible means of removing it. Dirty buildings usually
have a combination of dirt, soot, smoke, bird droppings, oil
stains, metal stains such as rust and copper, graffiti, paint,
tar, and\or organic stains left by moss, algae, lichen, fungi,
and ivy tendrils. The masonry itself may have developed a
dirty-looking protective crust that cannot be removed without
removing part of the masonry. One type of dirt found in urban
and industrial areas is grime, a black or gray crust formed by
the interaction of airborne particles from natural and industrial
sources with microorganisms like fungi, algae, or ivy secretions,
as well as byproducts from the breakdown of the masonry surface
itself.
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