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Substitute materials should be used only on a limited
scale and after careful research. Learn as much as
possible about the proposed materials, the fabricator, the
installer, the specifications for use, and any previous
experience with the material in a similar situation and
similar environment. Some materials are too new to have a
real track record. Although they may look promising, they
should not be used unless the manufacturers, fabricators,
and/or installers can supply satisfactory information on:
Appearance. Does the substitute material match the
original in color, texture, shape, etc.? Will its use
change the appearance of the building in any important
way?
Physical Properties. Is the chemical composition of
the new material similar to that of the original?
Will it react in the same way to exposure to sunlight,
moisture, pollution, and temperature changes? Will it
expand and contract at the same rate? Will it absorb
moisture in the same way? Does it have similar
tensile and compressive strengths (i.e., does it react
to weight and movement stresses in the same way as the
original)? If the answer to any of these questions is
no, can the new material be installed in a way that
will compensate for the differences? Will differences
between old and new materials cause damage to the
historic fabric of the building? In old buildings,
the historic material is almost always weaker than new
material and needs to be protected from stresses
caused by trapped moisture and uneven expansion and
contraction rates.
Performance. Will the substitute material hold up
over time? Will it need special care or frequent
maintenance once it has been installed?
4.17.1 Cast Aluminum Attributes.
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Material. Cast aluminum is a molten aluminum alloy cast
in permanent metal molds or in one-time sand molds. Color
is from paint applied to primed aluminum or from a
factory-finished coating. Small sections can be bolted
together to achieve intricate or sculptural details. Unit
castings are also available for items such as column
plinth blocks.
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Uses. Cast aluminum can be used as a substitute for
cast-iron or other decorative elements, grillwork, roof
crestings, cornices, ornamental spandrels, storefront
elements, column capitals, column bases and plinth blocks.
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