Page 104 - Masonry and Concrete

Understanding Masonry
103
UNDERSTANDING MASONRY

4.4 Cast Stone and Cultured Stone

Cast stone is a fine-grained precast concrete product manufactured to
resemble natural stone, with the same finish as stone which has been
cut and dressed to precise shape and dimension. Despite its name, cast
stone is more closely related to concrete and concrete masonry than to
natural stone. Cast stone is used for decorative accessory elements in
masonry construction. Cultured stone or “simulated” stone is another
manufactured product which looks like rustic stone and is used as a
veneer.
Cast stone is made of a carefully proportioned mix containing nat-
ural gravel, washed and graded sand, and crushed and graded stone
such as granite, marble, quartz, or limestone. White portland cement
usually is used to produce light colors and color consistency, although
grey cement and color pigments are sometimes blended with the white
cement. Because a rich cement-aggregate ratio of 1:3 is normally used,
cast stone properly cured in a warm, moist environment is dense, rel-
atively impermeable to moisture, and has a fine-grained, natural tex-
ture. Cast stone is relatively heavy, and its compressive strength is
higher than ordinary cast-in-place concrete. Most cast stone manufac-
turers produce and stock standard items of architectural trim such as
balusters, corner quoins, door pediments, and balcony rails (Figure 4-
14). Any shape which can be carved in natural stone can generally be
reproduced in cast stone at a lower cost. Cast stone may also simulate
the appearance of small, roughly hewn quarried stone or weathered
natural stone from fields or riverbeds. The color of the cement and the
type of aggregate can be varied depending on the desired appearance.
To produce a simulated white limestone, for instance, white portland
cement and limestone dust are used (Figure 4-15). Cast rubble stone is
generally less expensive than natural stone and easier to lay because it
is more regular in size and shape and does not require field trimming.

4.5 Natural Stone

There are many different ways to describe stone. It can be identified by
the form in which it is used—rubble, ashlar, or flagstone. It can be
identified by its type or mineral composition—granite, limestone,

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