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 Retain the original or early
Do not use electric saws or
hammers to remove mortar.
color and texture of masonry
surfaces wherever possible.
Brick or stone surfaces may
Do not remove paint from
masonry surfaces unless it is
have been painted or
necessary. This may subject
whitewashed for practical or
the building to damage and may
aesthetic reasons.
change its historical
appearance.
Repair or replace where
necessary, deteriorated
material with new material
that duplicates the old as
closely as possible.
(Further discussion of masonry maintenance problems and
recommended solutions may be found in Sections 4.3, Moisture
Problems; 4.4, Cleaning and Coatings; 4.5, Structural
Maintenance; 4.9, Exterior Wall Systems: and 4.17, New and
Substitute Materials.)
4.2.2 Metal. Metals found in historic structures include
wrought and cast iron, tin, lead, zinc, copper, bronze, brass,
lead, steel, terne, nickel and nickel alloys, stainless steel,
and aluminum. These metals are found as nails, hardware, roofs,
decorative crestings, balusters, domes, cupolas, railings,
interior and exterior stairways, window tames, window frames,
masonry anchors, girders, trusses, paint, and walls--almost
anything and everything a building might contain, from structure
to decoration. In order to stop metal deterioration and repair
damage, it is essential, but not always easy, to identify the
metal. Most metal problems are caused by water, corrosion, or
galvanic reactions.
o
Corrosion. Architectural metals most often deteriorate
through corrosion (also called oxidation), the chemical
reaction of a metal with oxygen or other substances. The
corrosion attack may be uniform (the metal corrodes evenly
wherever it is exposed to corrosive agents) or selective
(certain parts are affected more than others because of a
difference in composition of the parts). Corrosion can
take many forms:
-Pitting.
-Stress corrosion cracking (caused when wrought, or
worked metal reacts to chemicals in the environment) .
-Erosion (caused by abrasion that exposes fresh metal to
corrosive agents) .
-Galvanic corrosion (an electrochemical reaction to
contact between two different metals, such as an iron
nail in a copper roof).
4-13
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