Geoscience Reference
In-Depth Information
Building stone
2
a substantial area of business for the petrographer in
their own right and are therefore considered separately in
Chapter 3. Road paving applications were historically one
of the largest uses of stone in construction. Today the
use of stone setts, kerbs, and paving is restricted to
'streetscape' projects where a particular appearance is
required or for repairs of existing stone paving.
Of the immense variety of building stones that are
available, all may be classified geologically as being in
one of three broad groups. All stones are rock that are
either of igneous, sedimentary, or metamorphic origin,
depending on their composition and how they were
formed. Each of these three groups will be discussed in
detail in subsequent sections.
The marketing of stone has resulted in a wide variety
of nonscientific stone names being introduced into the
building stone industry. This can cause confusion when
trying to determine the identity and source of particular
stone types. The definitive name for any stone is its
'petrographic name', which is the geological identity
determined by petrographic examination. Additionally,
stones are likely to have a 'commercial name' for
marketing purposes, which may relate to traditional stone
names for the area of production or may be just a
marketing tool. The stone industry groups stone types
into 'commercial groups' as shown in
Table 4 (overleaf)
.
In this chapter both the petrographic name and (if
available) the commercial name will be included for each
of the stone types discussed. The commercial name will
be identified by single quotation marks.
The principal applications of petrographic
examination to building stone investigations are:
• Initial suitability assessment of stone from new
sources.
• Routine quality assurance of stone from the factory
production run.
• Confirming the identity/quality of stone for
purchasers.
• Diagnosing the causes of in-service
deterioration/failure.
• Matching stone types for restoration of historic
buildings.
Stone, the primary geomaterial, has been used for
building since man gave up the nomadic lifestyle of a
hunter-gatherer and began to build permanent
settlements. Natural stone is used in civil engineering for
structural elements, facing and cladding, and hard
landscaping. Current uses of natural stone in buildings
include load-bearing and self-supporting masonry,
masonry façades to framed buildings, cladding and
lining, roofing, flooring, and miscellaneous elements.
The earliest stone structures were probably masonry
constructed of unworked stone laid dry. Some ancient
masons used stone blocks with close-fitting joints not
requiring mortar. These often utilized blocks so large that
they would not subsequently shift, only occasionally
incorporating metal dowels for added stability. More
commonly, less precisely worked masonry units were used,
which had to be set in mortar to add stability to a wall or
building and make it weatherproof. Traditional stone walls
may be constructed from roughly squared blocks (random
rubble) or with dressed regular layers (coursed). Building
stone that has been selected, trimmed, and cut to specific
shapes and sizes is referred to as 'dimension stone'.
Traditional load-bearing masonry materials are inherently
strong in compression and comparatively weak in tension.
This has led to the development of masonry structures that
generate only very small tensile stresses such as the arch,
the vault, and the dome.
To take the required load, masonry walls for buildings
more than three storeys high must be of great thickness
and are consequently slow and expensive to construct.
From the late 1800s these problems were overcome by
the use of steel and reinforced concrete frames, which
support the floors and walls on the beams of the frame.
Modern cladding systems use relatively thin panels of
stone that are individually attached to the frame with
metal fixings.
Stone is also used as a prestige material for internal
flooring and lining. Another significant application is
stone roofing, with natural slate roofing being of
particular importance. Slate investigations have become
