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 How are units to be installed and anchored?
Have performance standards been developed to ensure
color stability?
Have large samples been delivered to the site for
color, finish, and absorption testing? Has mortar
been matched to adjacent historic mortar to achieve a
good color/tooling match?
Are fabricators/installers experienced?
4.17.3 Precast Concrete Attributes.
o Material. Precast concrete is a wet mix of cement and
aggregate poured into molds to create masonry units.
Molds can be made from existing good surfaces on the
building. Color is generally integral to the mix as a
natural coloration of the sand or aggregate, or as a
pigment. To avoid unsightly air bubbles that result from
the natural curing process, great care must be taken in
the initial and long-term vibration of the mix. Because
of its weight, it is generally used to produce individual
units of masonry, not thin shell panels.
Uses. Precast concrete is `generally used in place of
o
masonry materials (e.g., stone or terra cotta) . It is
used both for flat wall surfaces or for textured or
ornamental elements (e.g., wall stones, window and door
surrounds, stair treads, paving pieces, parapets, urns,
balusters, and other decorative elements) . Unlike
dry-tamped cast stone, surface texture is created by mold
rather than hand tamping.
Advantages.
o
Easily fabricated, takes shape well;
Rubber molds can be made from building stones;
Minimal shrinkage;
Can be load bearing, or anchorage system can be cast
in;
Expansion/contraction rate similar to stone:
Material is fire-rated;
Range of color and aggregate available;
Vapor permeable.
4-60
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