Identify, Retain and Preserve
Identifying, retaining, and preserving architectural
metal features such as columns, capitals, window hoods,
or stairways that are important in defining the overall
historic character of the building; and their finishes
and colors. Identification is also critical to differentiate
between metals prior to work. Each metal has unique
properties and thus requires different treatments.
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The ongoing maintenance and repair of historic architectural metals is emphasized in the treatment, Preservation. This shows a detail of a well-maintained polychromed cast-iron
facade in Petaluma, California, 1886 (O'Connell
and Lewis, Architectural Iron Works, San Francisco).
Photo: Don Meacham.
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Altering architectural metal features which are important
in defining the overall historic character of the building
so that, as a result, the character is diminished.
Replacing historic metal features instead of repairing
or replacing only the deteriorated metal.
Changing the type of finish or its historic color or
`accent scheme.
Stabilize
Stabilizing deteriorated or damaged architectural
metals as a preliminary measure, when necessary, prior
to undertaking appropriate preservation work.
Failing to stabilize deteriorated or damaged architectural
metals until additional work is undertaken, thus allowing
further damage to occur to the historic building.
Protect and Maintain
Protecting and maintaining architectural metals from
corrosion by providing proper drainage so that water
does not stand on flat, horizontal surfaces or accumulate
in curved, decorative features.
Cleaning architectural metals, when appropriate,
to remove corrosion prior to repainting or applying
other appropriate protective coatings.
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Where chemical paint stripping is involved,
careful planning of the sequence of work and inspection
by an architect or conservator to ensure strict
compliance with the contract documents is important
to minimize the risk of problems. Photo: Raymond
M. Pepi, Building Conservation Associates.
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Identifying the particular type of metal prior to
any cleaning procedure and then testing to assure that
the gentlest cleaning method possible is selected or
determining that cleaning is inappropriate for the particular
metal.
Cleaning soft metals such as lead, tin, copper,
terneplate, and zinc with appropriate chemical methods
because their finishes can be easily abraded by blasting
methods.
Using the gentlest cleaning methods for cast iron,
wrought iron, and steel--hard metals--in order to remove
paint buildup and corrosion. If handscraping and wire
brushing have proven ineffective, low pressure grit
blasting may be used as long as it does not abrade or
damage the surface.
Applying appropriate paint or other coating systems
after cleaning in order to decrease the corrosion rate
of metals or alloys.
Repainting with colors that are appropriate to the
historic building or district.
Applying an appropriate protective coating such
as lacquer to an architectural metal feature such as
a bronze door which is subject to heavy pedestrian use.
Evaluating the existing condition of the architectural
metals to determine whether more than protection and
maintenance are required, that is, if repairs to features
will be necessary.
Failing to identify, evaluate, and treat the causes
of corrosion, such as moisture from leaking roofs or
gutters.
Placing incompatible metals together without providing
a reliable separation material. Such incompatibility
can result in galvanic corrosion of the less noble metal,
e.g., copper will corrode cast iron, steel, tin, and
aluminum.
Exposing metals which were intended to be protected
from the environment.Applying paint or other coatings
to metals such as copper, bronze, or stainless steel
that were meant to be exposed.
Using cleaning methods which alter or damage the historic
color, texture, and finish of the metal; or cleaning
when it is inappropriate for the metal.
Removing the patina of historic metal. The patina may
be a protective coating on some metals, such as bronze
or copper, as well as a significant historic finish.
Cleaning soft metals such as lead, tin, copper, terneplate,
and zinc with grit blasting which will abrade the surface
of the metal.
Failing to employ gentler methods prior to abrasively
cleaning cast iron, wrought iron or steel; or using
high pressure grit blasting.
Failing to re-apply protective coating systems to metals
or alloys that require them after cleaning so that accelerated
corrosion occurs.
Using new colors that are inappropriate to the historic
building or district.
Failing to assess pedestrian use or new access patterns
so that architectural metal features are subject to
damage by use or inappropriate maintenance such as salting
adjacent sidewalks.
Failing to undertake adequate measures to assure the
protection of architectural metal features.
Repair
Repairing, stabilizing, and conserving fragile architectural
metals using well-tested consolidants, when appropriate.
Repairs should be physically and visually compatible
and identifiable upon close inspection for future research.
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This detail of a repaired historic cornice shows the zinc modillion and the leaf and egg and dart moldings after Preservation work, including repainting of the elements, has been completed. Photo: Michael Devonshire.
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Repairing architectural metal features by patching,
piecing-in, or otherwise reinforcing the metal using
recognized preservation methods. The new work should
be unobtrusively dated to guide future research and
treatment.
Removing architectural metals that could be stabilized
and conserved; or using untested consolidants and untrained
personnel, thus causing further damage to fragile historic
materials.
Removing architectural metals that could be repaired,
using improper repair techniques, or failing to document
the new work.
The following work
is highlighted to indicate that it represents
the greatest degree of intervention generally
recommended within the treatment Preservation,
and should only be considered after protection,
stabilization, and repair concerns have been addressed.
Limited Replacement in Kind
Replacing in kind extensively deteriorated
or missing parts of architectural metal features
when there are surviving prototypes such as porch
balusters, column capitals or bases, or porch
cresting. The new work should match the old in
material, design, and texture; and be unobtrusively
dated to guide future research and treatment.
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Another example shows one metal modillion (left side of cornice) that has sustained damage from a faulty gutter. The damaged modillion will be replaced in kind during the Preservation work, while the intact elements of the historic cornice will be maintained and preserved.
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Replacing an entire architectural metal feature
such as a column or balustrade when limited replacement
of deteriorated and missing parts is appropriate.
Using replacement material that does not match
the historic metal feature; or failing to properly
document the new work.
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