Granite
Content
GRANITE
The term granite has been applied to almost any igneous stone that can retain a
polish. True granites provide many of these stones but other types of igneous
stone that may fall into this classification include syenites, gabbros, dolerites,
and diorites. The metamorphic stones gneiss, schist and granulite are frequently
also included in this 'granite' classification.
The formation of these igneous rocks by the slow cooling of molten minerals such
as quartz, feldspar and hornblende has resulted in a wide variety of colours and
grain patterns.
In the United Kingdom the quarrying of granite is concentrated in a small number
of locations. Those of particular importance may be found in Devon and
Cornwall, Cumbria, at Peterhead and Aberdeen and on the east coast of
Scotland.
The main sources for imported granite are Scandinavia, South Africa, Sardinia,
Portugal, Spain, India, North America, China and Brazil.
pplications
The interlocking crystal structure imparts both the high strength and low porosity
necessary for a wide range of applications other than just flooring; these
characteristics are also important in allowing successful use of slabs that are
thinner than other types of stone.
Appearance
The immense colour choice includes fine and medium grained silver grey from
Devon and Cornwall and fine grained pink from Scotland, whilst other countries
provide dense, very fine grained materials with reflective crystals such as
larvikite (e.g. blue and emerald pearl) from Norway; reds from Scandinavia and
India; large grained brown from Finland; yellows from Brazil; and the delicately
mottled greys, fawns and pinks from Sardinia.
The surface finish affects the appearances of granite and those available include
sawn, flame textured, dolly pointed, fine axed, rough punched, honed, bush
hammered and water jet. It is in the gloss polished form, however, that these
granites reveal fully their colours and grain patterns.
Performance
Very hardwearing and physically strong, granite is largely unaffected by erosion,
pollution or atmospheric attack. Facades are generally self cleaning, although
eye level areas benefit from occasional cleaning as for glazing. A polished finish
is almost indestructible.
SANDSTONE
The term sandstone is used to describe almost any stone of sedimentary origin
with a granular texture. Some other types of stone that may fall under this
classification include gritstones, siltstones, greywackes, conglomerates and
marls. Aside from particle size variations, the dominant factor affecting
sandstone performance is the grain cement that may be siliceous, calcareous,
clay bearing or iron-rich.
Geologically it is a sedimentary type rock made up of various mineral particles
mainly quartz, mica and felspar. All these minerals are bonded together with
natural cements such as silicas, calcium carbonates, iron oxides and clays. The
individual make up of each sandstone gives a wide range of colours. A pure silica
sandstone is white with the colours arising from other minerals. Iron oxides can
cause the stone to vary from buff or brown through to the deepest red. Grey
colour stone is due to the presence of clay and green could indicate the presence
of glauconite which contained potassium.
Sandstone is a natural material traditionally regarded as the building stone of the
North. However, sandstone can be seen throughout the United Kingdom in many
prestigious buildings from structures which form part of our heritage to modern
office blocks.
Sandstone is traditionally used as a building material in many areas where it
occurs locally particularly in Derbyshire, Yorkshire and the North East of England,
Wales and Scotland. Many of the "stone cities" of the North derive their particular
architectural character from the use of sandstone.
Most of the major sandstone quarries working today are located in the North of
England, Derbyshire and Scotland. For flooring purposes, sandstones are also
imported.
Appearance
Sandstone has many colours ranging from white, grey and buff to various shades
of
pink
and
red.
The colour and texture of stone is self evident, however the colour of dry stone
can change quite dramatically on wetting. Natural weathering can play a major
part in the change of colour. Such colour change can sometimes be viewed on
abandoned faces of the quarry although it is much more important to view
existing
buildings
constructed
from
the
same
stone.
Sandstones generally have an even texture, which may vary from course to fine,
but the stone from some quarries also show attractive natural markings.
Applications
Many types of sandstone are suitable for paving or flooring. Some can be split
("riven") otherwise the normal finish is sawn. Tooled, sandblasted and flame
textured
finishes
are
also
available.
There is a vast variety of surface finishes available from the traditional rubble
walling to wrought stonework with its finishes to different forms ie. boasting,
pitched, broached, hammer dressed and rusticated, to the very intricate looking
vermiculated. But most importantly, credit must go to the craftsmen who hue the
sandstone to all the various forms from large stones with a high degree of
moulding to the most intricate of carving work. Sandstones are suitable for blcok
construction in most building and engineering work and can now be cut to
relatively thin sections for cladding to steel framed or concrete structured
buildings.
All in all sandstone is one of the few historic natural minerals still in use today. It
provides excellent durability and is virtually maintenance free. It is aesthetically
appealing to the eye whilst giving great value for money to the client.
Performance
Most sandstones have good load bearing and weathering properties. Correct
detailling with regard to weathering is of prime importance, especially on
buildings designed with sloping surfaces and without overhangs. Great care is
required in the design of non-ferrous cramps and corbels for fixing to structures.
SLATE
Slate is found extensively, throughout the British Isles and has, for centuries,
been a major source of building stone. Historically, and, in common with other
stones, it was first used in and around the immediate areas of availability.
The term slate is often used to describe any rock that can be easily split into thin
sheets, principally for roofing purposes. True slate is defined by the presence of a
'slaty' cleavage; this allows the slate to be split at almost any point through the
stone parallel to the cleavage plane. Most true slates are metamorphosed
sediments, often formerly mudstones; however, some British "slates" are derived
from volcanic ash sequences and are not true slates in the strict geological
sense.
Appearance
The major UK sources of slate, with their distinctive colours, are the Lake District
blue/grey, light green, olive green and silver grey, North Wales blue, grey, blueblack and red, and Cornwall - grey.
Slate is easily split ("riven") into thin sections, giving a natural finish. Other
finishes include sawn, sanded, fine rubbed, flame textured, bush hammered and
water jet.
Applications
From the very early, basic applications, British Slate is now used for very wide
and diverse purposes. Modern quarrying and machine processes allow prime
blocks to be sawn or split into large slabs and a variety of thicknesses. Current
products include: roofing, cladding, cills, copings, flooring & paving, treads,
plaques & memorials, worktops & fireplaces.
Slate is typically a very durable construction material and rarely exhibits visible
degradation, even when placed under extreme atmospheric conditions for many
years. For flooring purposes U.K. slate is unlikely to delaminate or exhibit
efflorescence.
High flexural strength and typically very low porosity makes slate eminently
suitable for flooring purposes and it requires little maintenance.
Caution should be exercised when choosing material marketed as slate as some
may not be suitable for flooring. If any doubt exists about the material being
considered,
specialist
advice
should
be
sought.
Very thin, split, natural riven sections are used for roofing and the same methods
produce thicker material for flooring and cladding. Slate is readily available in
sawn, fine rubbed and other finishes wuch as sand-blasted and flame textured.
Performance
British Slate has a proven record of durability and being supplied fit for its
intended purposes. This is readily seen on countless buildings in the UK and
many areas of the world. Such examples of installation are witness to the ability
of slate to withstand the rigours of extreme atmospheric conditions. Slate is
extremely stable and will not degrade, warp or twist. Quality Assurance,
management systems are widely used throughout the industry.
LIMESTONE
Stone is a material that man has used in building for several thousand years and
it still lends itself to modern usage and design, and limestone in its various
geological forms is probably the type of natural stone most widely used for this
purpose. It occurs naturally in many parts of the UK with the limestones of the
Jurassic period being those of most importance in this field. They run broadly in a
belt from Dorset and Somerset in the south west, through the Cotswolds and
Oxfordshire, on into Northamptonshire and Lincolnshire, to just north of the
Humber.
Limestone is a sedimentary rock. Many of the commonly used varieties were
formed by the accretion of the hard remains of former organisms such as corals
and shells. These materials principally comprise calcium carbonate (calcite), as
does the cement. Calcite is a relatively soft mineral and careful selection will be
needed when you choose this for use as flooring. Variations in the types and
quantities of shell and other remains and the nature of the cement provide a
huge range in the types of limestone available.
The limestones of these areas were used for building in Roman times and, in
later centuries and to-date, have been the traditional building material of their
localities, many buildings throughout these counties bear witness to this. In
addition, some limestones are extensively used outside their areas of origins as
is evidenced by the many fine buildings to be seen throughout the British Isles,
particularly in major cities and towns. Cathedrals, churches and numerous public
and private buildings provide outstanding examples of the durability and beauty
of these limestones and they show through the skill of the mason, how this stone
is so eminently suitable for producing masonry of excellence in all aspects of
plain and detailed work that may be required. Among the better known
limestones of the Jurassic age are those of Purbeck, Clipsham, Ancaster, Ketton,
Bath, Doulting and Weldon, whilst Portland stone is a characteristic feature of
London architecture. From the earlier Carboniferous age come the limestones of
Derbyshire and Cumbria such as Hopton Wood, Sheldon, Orton Scar and
Salterwath.
Imported limestones, most notably French, German, Portuguese, Spanish,
Turkish,
Egyptian
and
Israeli
are
also
available
in
the
UK.
Appearance
The colours of limestones range from almost white to the warm honey tone of
Bath stones with grey/blue and darker browns a feature in some limestones.
Textures range from fine even grained stones to the smooth fossil bearing types
and to the coarse open textured Portland roach. Certain limestones such as
Purbeck and Hopton Wood take a polish and can be used as "marbles".
Applications
Limestones are used extensively in both new building and restoration where their
ease of working facilitates the production of cladding, ashlar and other forms of
walling.
They
are
also
suitable
for
flooring.
Many limestones are particularly suited to carved and moulded work.
Components such as cills and jambs, soffits and copings, heads and mullions are
readily produced to add interest and enrichment to building facades.
Performance
Limestones generally have good load bearing properties and weathering
characteristics although correct detailing is important as with all building
materials. Limestones must not be used above sandstones on exterior
elevations.
The properties of individual types of stone can vary considerably and advice
should always be sought on the selection of suitable stones, both for general and
particular applications.
MARBLE
True marbles in the geological sense are metamorphosed limestone and are
principally composed of recrystallised calcite formed into an interlocking granular
structure. Some hard or partially metamorphosed limestones are incorrectly
referred to as marble, even though they exhibit many of the characteristics of
marble.
In its 'purest' state marble is typically white, however the presence of other
minerals can often provide colour(s). In some cases the colour appears as
irregular shaped patches (brecciation) or as substantial veining. Specialist advice
should be obtained as to the suitability of such marbles in particular locations.
Greater care must also be taken during installation as other construction defects
easily taint the pureness of marble, particularly from underlying materials, and
may result in staining at a later date.
It is common to use marble with a highly polished surface finish and, as a
consequence, slip resistance should be carefully considered. Marble is imported.
QUARTZITES
Quartzites are typically the metamorphosed product of an original sedimentary
rock e.g. sandstone, composed almost entirely of quartz.
In general quartzites are hard wearing, have low porosity, a high compressive
strength and good durability making them suitable for use as flooring. The
metamorphic varieties in particular may be brittle and so some care is required
in assessing a material prior to use. While composed largely of quartz, the
presence of some impurities can lead to the development of different colours and
the typical range is from white to yellowish brown, through to green, brown, gold,
grey and blue. In Eire, the metamorphic quartzites have a complex geological
history which has tended to result in them having a relatively small natural block
size. All operating quartzite quarries in the British Isles occur in Eire. Elsewhere
quartzites are commercially available from Norway, Sweden, Italy, South Africa,
USA and Brazil.
TRAVERTINE
Travertine is the name normally given to a type of precipitated calcite associated
with the cooling of waters around hot springs or in caves. Being formed very
slowly it often incorporates dead matter such as tree debris that later rots away
to leave a voided structure.
The performance of travertine greatly depends on the size and density of the
voids, which, in most instances, are routinely resin surface filled before the
finished stone is supplied. The nature of the fill material must be compatible with
the travertine and not subject to discoloration or decay.
Traditionally travertine was naturally bedded and generally referred to as vein
cut. Recently travertine cut face bedded and referred to as classico has appeared
on the market. Whilst the vein cut material has a long and proven history of use,
the cross cut or classico travertine has not yet proved to be as suitable because
of surface collapse and filler failure. Before this material is considered, its
limitations in performance must be taken into account.
Generally travertine is suitable only for internal flooring purposes, and then only
after the most careful consideration. Strength may be lower than most other
stones and the presence of hidden voids below the surface may lead to ongoing
repair when the filling material collapses.
Unfilled travertine has been used for flooring purposes but only after strict
quality control of the size and distribution of the voids. All travertine is imported.
GREEN MARBLE OR VERDE
Green or verde marble is considered separately to true marble because its origin
is often the result of the metamorphism of rocks other than limestones. The
green colour is typically derived from the presence of serpentine minerals. These
minerals are relatively soft and the structure often weak, the stone commonly
requiring reinforcement from matting glued to the underside.
Verdes are rarely used for whole floors and are preferred for providing coloured
inserts to other flooring materials. Care must always be taken to ensure their
compatibility with other stones.
A special consideration for any verde is the presence or otherwise of asbestiform
minerals that may be naturally present e.g. chrysotile (white asbestos) and the
amphiboles tremolite and actinolite. It may be prudent to establish that, where
present, fibres of these minerals in the respirable range are not generated during
any cutting, grinding and polishing operations, particularly if carried out dry.
The Asbestos (Prohibitions) Regulations have banned the import, supply and use
of blue, brown and white asbestos (crocidolite, amosite and chrysotile
respectively) essentially when part of an asbestos admixture product. Natural
stone that contains chrysotile for example, and is used for flooring, would not be
classed as an asbestos admixture product.
Ashlar: A horizontal stone pattern generally made from squared and rectangular
shapes having sawed or dressed beds of joints.
- Coursed Ashlar: Ashlar set to form continuous horizontal joints with one rise.
- Stacked Ashlar: Ashlar set to form continuous vertical joints.
- Random Ashlar: Ashlar set with stones of varying length and height so that
neither vertical nor horizontal joints are continuous.
5.3.3 Ashlar-faced solid wall
With this wall type, (Figures 13 (a) and (b)) the dressed stone is attached using
stainless-steel wall ties or brick reinforcement to a concrete block or brickwork
background structure. Whether or not the stone facing acts compositely with the
background structure and carries structural loads depends on the way in which
the stone facing and backing structure are bonded or tied together. Normal
cavity wall ties will not be sufficient to enable a full transfer of load to take place
between the two leaves of a solid wall. The stone is essentially designed to
carry it own weight and to resist wind loads. To ensure composite structural
action it is necessary to build the wall with bonder stones built into the backing
structure (refer to Section 6 for further information). The issues relating to
course heights and joint widths outlined in Sections 5.1.1 and 5.3.1 apply
equally to ashlar-faced solid walls.
Stone suppliers are able to provide a number of different surface finishes and
textures to dressed stone to suit a range of joint widths. It is advisable to consult
45the stone supplier or specialist on the most appropriates stone finishes for
particular joint widths.
The term granite has been applied to almost any igneous stone that can retain a
polish. True granites provide many of these stones but other types of igneous
stone that may fall into this classification include syenites, gabbros, dolerites,
and diorites. The metamorphic stones gneiss, schist and granulite are frequently
also included in this 'granite' classification.
The formation of these igneous rocks by the slow cooling of molten minerals such
as quartz, feldspar and hornblende has resulted in a wide variety of colours and
grain patterns.
In the United Kingdom the quarrying of granite is concentrated in a small number
of locations. Those of particular importance may be found in Devon and
Cornwall, Cumbria, at Peterhead and Aberdeen and on the east coast of
Scotland.
The main sources for imported granite are Scandinavia, South Africa, Sardinia,
Portugal, Spain, India, North America, China and Brazil.
pplications
The interlocking crystal structure imparts both the high strength and low porosity
necessary for a wide range of applications other than just flooring; these
characteristics are also important in allowing successful use of slabs that are
thinner than other types of stone.
Appearance
The immense colour choice includes fine and medium grained silver grey from
Devon and Cornwall and fine grained pink from Scotland, whilst other countries
provide dense, very fine grained materials with reflective crystals such as
larvikite (e.g. blue and emerald pearl) from Norway; reds from Scandinavia and
India; large grained brown from Finland; yellows from Brazil; and the delicately
mottled greys, fawns and pinks from Sardinia.
The surface finish affects the appearances of granite and those available include
sawn, flame textured, dolly pointed, fine axed, rough punched, honed, bush
hammered and water jet. It is in the gloss polished form, however, that these
granites reveal fully their colours and grain patterns.
Performance
Very hardwearing and physically strong, granite is largely unaffected by erosion,
pollution or atmospheric attack. Facades are generally self cleaning, although
eye level areas benefit from occasional cleaning as for glazing. A polished finish
is almost indestructible.
SANDSTONE
The term sandstone is used to describe almost any stone of sedimentary origin
with a granular texture. Some other types of stone that may fall under this
classification include gritstones, siltstones, greywackes, conglomerates and
marls. Aside from particle size variations, the dominant factor affecting
sandstone performance is the grain cement that may be siliceous, calcareous,
clay bearing or iron-rich.
Geologically it is a sedimentary type rock made up of various mineral particles
mainly quartz, mica and felspar. All these minerals are bonded together with
natural cements such as silicas, calcium carbonates, iron oxides and clays. The
individual make up of each sandstone gives a wide range of colours. A pure silica
sandstone is white with the colours arising from other minerals. Iron oxides can
cause the stone to vary from buff or brown through to the deepest red. Grey
colour stone is due to the presence of clay and green could indicate the presence
of glauconite which contained potassium.
Sandstone is a natural material traditionally regarded as the building stone of the
North. However, sandstone can be seen throughout the United Kingdom in many
prestigious buildings from structures which form part of our heritage to modern
office blocks.
Sandstone is traditionally used as a building material in many areas where it
occurs locally particularly in Derbyshire, Yorkshire and the North East of England,
Wales and Scotland. Many of the "stone cities" of the North derive their particular
architectural character from the use of sandstone.
Most of the major sandstone quarries working today are located in the North of
England, Derbyshire and Scotland. For flooring purposes, sandstones are also
imported.
Appearance
Sandstone has many colours ranging from white, grey and buff to various shades
of
pink
and
red.
The colour and texture of stone is self evident, however the colour of dry stone
can change quite dramatically on wetting. Natural weathering can play a major
part in the change of colour. Such colour change can sometimes be viewed on
abandoned faces of the quarry although it is much more important to view
existing
buildings
constructed
from
the
same
stone.
Sandstones generally have an even texture, which may vary from course to fine,
but the stone from some quarries also show attractive natural markings.
Applications
Many types of sandstone are suitable for paving or flooring. Some can be split
("riven") otherwise the normal finish is sawn. Tooled, sandblasted and flame
textured
finishes
are
also
available.
There is a vast variety of surface finishes available from the traditional rubble
walling to wrought stonework with its finishes to different forms ie. boasting,
pitched, broached, hammer dressed and rusticated, to the very intricate looking
vermiculated. But most importantly, credit must go to the craftsmen who hue the
sandstone to all the various forms from large stones with a high degree of
moulding to the most intricate of carving work. Sandstones are suitable for blcok
construction in most building and engineering work and can now be cut to
relatively thin sections for cladding to steel framed or concrete structured
buildings.
All in all sandstone is one of the few historic natural minerals still in use today. It
provides excellent durability and is virtually maintenance free. It is aesthetically
appealing to the eye whilst giving great value for money to the client.
Performance
Most sandstones have good load bearing and weathering properties. Correct
detailling with regard to weathering is of prime importance, especially on
buildings designed with sloping surfaces and without overhangs. Great care is
required in the design of non-ferrous cramps and corbels for fixing to structures.
SLATE
Slate is found extensively, throughout the British Isles and has, for centuries,
been a major source of building stone. Historically, and, in common with other
stones, it was first used in and around the immediate areas of availability.
The term slate is often used to describe any rock that can be easily split into thin
sheets, principally for roofing purposes. True slate is defined by the presence of a
'slaty' cleavage; this allows the slate to be split at almost any point through the
stone parallel to the cleavage plane. Most true slates are metamorphosed
sediments, often formerly mudstones; however, some British "slates" are derived
from volcanic ash sequences and are not true slates in the strict geological
sense.
Appearance
The major UK sources of slate, with their distinctive colours, are the Lake District
blue/grey, light green, olive green and silver grey, North Wales blue, grey, blueblack and red, and Cornwall - grey.
Slate is easily split ("riven") into thin sections, giving a natural finish. Other
finishes include sawn, sanded, fine rubbed, flame textured, bush hammered and
water jet.
Applications
From the very early, basic applications, British Slate is now used for very wide
and diverse purposes. Modern quarrying and machine processes allow prime
blocks to be sawn or split into large slabs and a variety of thicknesses. Current
products include: roofing, cladding, cills, copings, flooring & paving, treads,
plaques & memorials, worktops & fireplaces.
Slate is typically a very durable construction material and rarely exhibits visible
degradation, even when placed under extreme atmospheric conditions for many
years. For flooring purposes U.K. slate is unlikely to delaminate or exhibit
efflorescence.
High flexural strength and typically very low porosity makes slate eminently
suitable for flooring purposes and it requires little maintenance.
Caution should be exercised when choosing material marketed as slate as some
may not be suitable for flooring. If any doubt exists about the material being
considered,
specialist
advice
should
be
sought.
Very thin, split, natural riven sections are used for roofing and the same methods
produce thicker material for flooring and cladding. Slate is readily available in
sawn, fine rubbed and other finishes wuch as sand-blasted and flame textured.
Performance
British Slate has a proven record of durability and being supplied fit for its
intended purposes. This is readily seen on countless buildings in the UK and
many areas of the world. Such examples of installation are witness to the ability
of slate to withstand the rigours of extreme atmospheric conditions. Slate is
extremely stable and will not degrade, warp or twist. Quality Assurance,
management systems are widely used throughout the industry.
LIMESTONE
Stone is a material that man has used in building for several thousand years and
it still lends itself to modern usage and design, and limestone in its various
geological forms is probably the type of natural stone most widely used for this
purpose. It occurs naturally in many parts of the UK with the limestones of the
Jurassic period being those of most importance in this field. They run broadly in a
belt from Dorset and Somerset in the south west, through the Cotswolds and
Oxfordshire, on into Northamptonshire and Lincolnshire, to just north of the
Humber.
Limestone is a sedimentary rock. Many of the commonly used varieties were
formed by the accretion of the hard remains of former organisms such as corals
and shells. These materials principally comprise calcium carbonate (calcite), as
does the cement. Calcite is a relatively soft mineral and careful selection will be
needed when you choose this for use as flooring. Variations in the types and
quantities of shell and other remains and the nature of the cement provide a
huge range in the types of limestone available.
The limestones of these areas were used for building in Roman times and, in
later centuries and to-date, have been the traditional building material of their
localities, many buildings throughout these counties bear witness to this. In
addition, some limestones are extensively used outside their areas of origins as
is evidenced by the many fine buildings to be seen throughout the British Isles,
particularly in major cities and towns. Cathedrals, churches and numerous public
and private buildings provide outstanding examples of the durability and beauty
of these limestones and they show through the skill of the mason, how this stone
is so eminently suitable for producing masonry of excellence in all aspects of
plain and detailed work that may be required. Among the better known
limestones of the Jurassic age are those of Purbeck, Clipsham, Ancaster, Ketton,
Bath, Doulting and Weldon, whilst Portland stone is a characteristic feature of
London architecture. From the earlier Carboniferous age come the limestones of
Derbyshire and Cumbria such as Hopton Wood, Sheldon, Orton Scar and
Salterwath.
Imported limestones, most notably French, German, Portuguese, Spanish,
Turkish,
Egyptian
and
Israeli
are
also
available
in
the
UK.
Appearance
The colours of limestones range from almost white to the warm honey tone of
Bath stones with grey/blue and darker browns a feature in some limestones.
Textures range from fine even grained stones to the smooth fossil bearing types
and to the coarse open textured Portland roach. Certain limestones such as
Purbeck and Hopton Wood take a polish and can be used as "marbles".
Applications
Limestones are used extensively in both new building and restoration where their
ease of working facilitates the production of cladding, ashlar and other forms of
walling.
They
are
also
suitable
for
flooring.
Many limestones are particularly suited to carved and moulded work.
Components such as cills and jambs, soffits and copings, heads and mullions are
readily produced to add interest and enrichment to building facades.
Performance
Limestones generally have good load bearing properties and weathering
characteristics although correct detailing is important as with all building
materials. Limestones must not be used above sandstones on exterior
elevations.
The properties of individual types of stone can vary considerably and advice
should always be sought on the selection of suitable stones, both for general and
particular applications.
MARBLE
True marbles in the geological sense are metamorphosed limestone and are
principally composed of recrystallised calcite formed into an interlocking granular
structure. Some hard or partially metamorphosed limestones are incorrectly
referred to as marble, even though they exhibit many of the characteristics of
marble.
In its 'purest' state marble is typically white, however the presence of other
minerals can often provide colour(s). In some cases the colour appears as
irregular shaped patches (brecciation) or as substantial veining. Specialist advice
should be obtained as to the suitability of such marbles in particular locations.
Greater care must also be taken during installation as other construction defects
easily taint the pureness of marble, particularly from underlying materials, and
may result in staining at a later date.
It is common to use marble with a highly polished surface finish and, as a
consequence, slip resistance should be carefully considered. Marble is imported.
QUARTZITES
Quartzites are typically the metamorphosed product of an original sedimentary
rock e.g. sandstone, composed almost entirely of quartz.
In general quartzites are hard wearing, have low porosity, a high compressive
strength and good durability making them suitable for use as flooring. The
metamorphic varieties in particular may be brittle and so some care is required
in assessing a material prior to use. While composed largely of quartz, the
presence of some impurities can lead to the development of different colours and
the typical range is from white to yellowish brown, through to green, brown, gold,
grey and blue. In Eire, the metamorphic quartzites have a complex geological
history which has tended to result in them having a relatively small natural block
size. All operating quartzite quarries in the British Isles occur in Eire. Elsewhere
quartzites are commercially available from Norway, Sweden, Italy, South Africa,
USA and Brazil.
TRAVERTINE
Travertine is the name normally given to a type of precipitated calcite associated
with the cooling of waters around hot springs or in caves. Being formed very
slowly it often incorporates dead matter such as tree debris that later rots away
to leave a voided structure.
The performance of travertine greatly depends on the size and density of the
voids, which, in most instances, are routinely resin surface filled before the
finished stone is supplied. The nature of the fill material must be compatible with
the travertine and not subject to discoloration or decay.
Traditionally travertine was naturally bedded and generally referred to as vein
cut. Recently travertine cut face bedded and referred to as classico has appeared
on the market. Whilst the vein cut material has a long and proven history of use,
the cross cut or classico travertine has not yet proved to be as suitable because
of surface collapse and filler failure. Before this material is considered, its
limitations in performance must be taken into account.
Generally travertine is suitable only for internal flooring purposes, and then only
after the most careful consideration. Strength may be lower than most other
stones and the presence of hidden voids below the surface may lead to ongoing
repair when the filling material collapses.
Unfilled travertine has been used for flooring purposes but only after strict
quality control of the size and distribution of the voids. All travertine is imported.
GREEN MARBLE OR VERDE
Green or verde marble is considered separately to true marble because its origin
is often the result of the metamorphism of rocks other than limestones. The
green colour is typically derived from the presence of serpentine minerals. These
minerals are relatively soft and the structure often weak, the stone commonly
requiring reinforcement from matting glued to the underside.
Verdes are rarely used for whole floors and are preferred for providing coloured
inserts to other flooring materials. Care must always be taken to ensure their
compatibility with other stones.
A special consideration for any verde is the presence or otherwise of asbestiform
minerals that may be naturally present e.g. chrysotile (white asbestos) and the
amphiboles tremolite and actinolite. It may be prudent to establish that, where
present, fibres of these minerals in the respirable range are not generated during
any cutting, grinding and polishing operations, particularly if carried out dry.
The Asbestos (Prohibitions) Regulations have banned the import, supply and use
of blue, brown and white asbestos (crocidolite, amosite and chrysotile
respectively) essentially when part of an asbestos admixture product. Natural
stone that contains chrysotile for example, and is used for flooring, would not be
classed as an asbestos admixture product.
Ashlar: A horizontal stone pattern generally made from squared and rectangular
shapes having sawed or dressed beds of joints.
- Coursed Ashlar: Ashlar set to form continuous horizontal joints with one rise.
- Stacked Ashlar: Ashlar set to form continuous vertical joints.
- Random Ashlar: Ashlar set with stones of varying length and height so that
neither vertical nor horizontal joints are continuous.
5.3.3 Ashlar-faced solid wall
With this wall type, (Figures 13 (a) and (b)) the dressed stone is attached using
stainless-steel wall ties or brick reinforcement to a concrete block or brickwork
background structure. Whether or not the stone facing acts compositely with the
background structure and carries structural loads depends on the way in which
the stone facing and backing structure are bonded or tied together. Normal
cavity wall ties will not be sufficient to enable a full transfer of load to take place
between the two leaves of a solid wall. The stone is essentially designed to
carry it own weight and to resist wind loads. To ensure composite structural
action it is necessary to build the wall with bonder stones built into the backing
structure (refer to Section 6 for further information). The issues relating to
course heights and joint widths outlined in Sections 5.1.1 and 5.3.1 apply
equally to ashlar-faced solid walls.
Stone suppliers are able to provide a number of different surface finishes and
textures to dressed stone to suit a range of joint widths. It is advisable to consult
45the stone supplier or specialist on the most appropriates stone finishes for
particular joint widths.
