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Historic Preservation - Technical Procedures
Copper: Characteristics, Uses And Problems
Developed For Hspg (Nps - Sero)
Copper: Characteristics, Uses And Problems
COPPER: CHARACTERISTICS, USES AND PROBLEMS
This standard includes general information on the characteristics
and common uses of copper and identifies typical problems
associated with this material along with common causes of its
Characteristics of Copper:
- Ductile: Can be drawn or "stretched"
- Malleable: Can be hammered or rolled into sheets without
Copper is initially bright reddish-brown in color, but when exposed
to the atmosphere, it acquires a protective patina that turns from
brown to black to green over an eight to ten year period. This
patina is a copper carbonate or copper sulfate formed on the
surface of the metal when hydrogen sulfide combines with oxygen or
sulfur dioxide. This naturally occurring corrosion resists further
corrosion. Though copper does corrode, this protective patina
makes copper a corrosion-resistant material.
Typical historical uses for copper included:
- Sheathing for ships
- Roofing and flashing: Sheet copper is light and easily
- Ornamental detailing such as weathervanes and finials
- Decorative detailing such as running moldings, sheathing on
oriel and bay windows, rain conductor heads, and other detail
fabricated to ornament the cornice lines of many buildings.
- Statues: Sections of sheet copper were often hammered over
wooden or other forms to create ornaments or statues. Once
the copper sheets had taken the shape of the form, they were
removed and soldered together over a wooden or metal
framework. The most famous example is the Statue of Liberty
which consists of copper sheeting over a steel framework.
Typical uses for copper in the 20th century include:
- Decorative detailing: Limited due to the high cost of copper.
- Flashing, gutters and downspouts: Used in small quantities.
- Piping systems: Copper's strength and resistance to corrosion
by most types of soils and water make it appropriate for use
- Electrical wiring, telephone wiring, and heating and air
conditioning systems: Copper's high capacity for thermal and
electrical conductivity makes it suitable for these
PROBLEMS AND DETERIORATION
Problems may be classified into two broad categories: 1) Natural
or inherent problems based on the characteristics of the material
and the conditions of the exposure, and 2) Vandalism and human-
Although there is some overlap between the two categories, the
inherent material deterioration problems generally occur gradually
over long periods of time, at predictable rates and require
appropriate routine or preventive maintenance to control.
Conversely, many human induced problems, (especially vandalism),
are random in occurrence; can produce catastrophic results; are
difficult to prevent, and require emergency action to mitigate.
Some human induced problems, however, are predictable and occur
NATURAL OR INHERENT PROBLEMS
1. Chemical corrosion:
a. Copper is attacked by alkalis, ammonia, and various
sulfate compounds that can combine with water to form
b. Some bituminous roofing cements will attack copper, as
will sulfate-reducing bacteria, which act as a catalyst
c. Copper is also attacked by rainwater that has become
acidic through contact with moss, lichen, algae, and
occasionally wood shingles. (The use of 16 oz. copper
sheets will often alleviate the problems associated with
2. Galvanic (Electrochemical) Corrosion:
a. Galvanic corrosion occurs when two dissimilar metals come
in contact with one another and an electrolyte, such as
rainwater, condensation, dew, fog, etc. is present. Such
a reaction will cause one or the other of the metals to
b. Direct contact of copper with other metals will cause
those metals to corrode. Iron, steel, zinc and
galvanized steel, tin and aluminum are especially
susceptible to corrosion if put into contact with copper.
1) Copper roofing fastened with other than copper or
brass fasteners will cause the fasteners to
2) Mixing metals used for flashing, gutters and
downspouts, decorative elements, windows or roof
covering will also cause galvanic corrosion.
VANDALISM OR HUMAN-INDUCED PROBLEMS
Mechanical or physical deterioration:
1. Erosion: Erosion of valley flashing and gutters is caused by
continuous exposure to rain and snow which scours the surfaces
as it drains.
2. Fatigue: Anything which restricts movement due to normal
expansion and contraction will cause fatigue. This can
a. The use of asphaltic building papers which will stick to
the backside of the copper sheets preventing them from
moving when heated by the sun.
b. The lack of an adequate number of transverse joints or
welts in a length of sheet copper between bays. Cracking
of the sheets will often result.
c. Improperly sized bays (space between vertical seams) or
the use of an inadequate number of fasteners. Using
copper sheets which are not rigid enough to resist this
movement will exacerbate the problem.
d. Inadequate support from the underside, such as spaced
rather than tight sheathing boards, will also result in
buckling and sagging of the sheet metal, ultimately
causing the metal to crack and tear.
END OF SECTION