In this section you will learn about:

• Identify the uses of clay products in the building industry
• Understand the role of brickwork in the building industry, and be familiar with the range of brick types and different styles of bonding and tinting,
• Describe the desirable qualities of stone for specific applications,
• Discuss the uses and limitations of stone as a building material.

Stone and clay are among the oldest of building materials.  The use of stone in particular dates back to prehistoric times and many ancient civilisations have appreciated the properties of stone and developed the art of using it.

Lack of timber or other materials sometimes forced the use of stone and in other cases, stone was the preferred material because of certain superior properties such as durability or prestige.  The natural enduring appearance of stone and its abundance have ensured its continued use as a building material to modern times.

Similarly, clay has endured as a building material and even in early times its use was widespread (eg. bricks, tiles, pipes and accessories).  The shaping of plastic clay and then hardening it by drying and firing, was perhaps humanity’s earliest form of manufacturing but it was not until the late nineteenth century that machines became involved in the manufacturing process.

Reference web sites

Think Brick Australia represents Australia’s leading clay brick and paver manufacturers. Its purpose is to make sure clay brick is recognised as a pre-eminent building material by leading architects, developers, builders and property owners.
Web site: www.thinkbrick.com.au/

 

Brick manufacturers

The following is a list of Australian brick manufacturers who have an online presence.
Austral Bricks: www.australbrick.com.au
Bendigo Brick Pty Ltd: www.bendigobrick.com.au/
Boral Bricks: www.boral.com.au
Bowral Brickworks: www.bowralbricks.com.au/
Hallett Brick: www.hallettbrick.com.au/
Littlehampton Brick Co.: http://littlehamptonbrick.com.au/
Metro Brick: www.metrobrick.com.au/
Midland Brick (a division of Boral): www.midlandbrick.com.au/#
Namoi Valley Brickworks: http://users.northnet.com.au/~nvbricks/index.html
Selkirk: www.selkirk.com.au/
PGH Bricks: www.pghclay.com.au/

Clay

Clays are natural materials made up of very small crystalline mineral fragments.  The shape, size and type of these fragments gives clays their plastic quality which allows them to be moulded and shaped when wet. These mineral fragments are also responsible for the hard, stony nature of clays after they are fired at high temperatures.

 

Clay products

When clay has been changed by heat (firing), the products are called ceramics. Different products require different firing temperatures, as shown in Table 1.  As temperature may vary, the figures given are only approximate.

 

Approx. firing temperature (°C)	Ceramic	Products
1350	Porcelain	electrical insulators
	Vitreous china	sanitary appliances
	Earthenware	glazes; tiles (for internal walls); some sanitary appliances
	Stoneware	drainpipes and fittings
	Fireclay	firebricks; flue liners
	Terracotta	floor and roofing tiles; air bricks; chimney pots
100-1050	Bricks	structural and decorative brickwork

Table 1: Table of firing temperatures and uses of various ceramics

During firing, water is driven off, some recrystallisation of minerals takes place, and glass is formed from quartz sand is present in the clay.  The result is a hard, insoluble material.  The higher the firing temperature, the more recrystallisation occurs and the more glass is formed, resulting in greater hardness and density.

The minerals present in the clay will determine its colour when fired.
Ceramics are also coloured by having a specially prepared coating, or slip, applied before firing, which results in a glaze of the required colour or texture.

Uses of ceramics in building

There are five types of ceramics, apart from bricks, that are mainly used in building. 
Table 2 shows how these different ceramics are made and used.

	Features	Firing temperature	Uses
Terracotta	Yellow to brownish red clays, which may be glazed or unglazed.  Terracotta roofing tiles, although brittle, are stable in high climatic temperatures and do not contaminate run-off water	Fairly low temperature	Main use is for floor and roofing tiles and air bricks (ventilators).  Over the years, the most common pattern seen in Australia has been the French or Marseilles pattern (refer to fig 4.1).
Fireclay	Usually a creamish colour, it can withstand high temperatures over a period of time without cracking		Flue liners and firebricks in stoves, fireplaces, kilns and furnaces
Stoneware	Harder, and less absorbent than fireclay.  Contains more glass	Fired at a higher temperature than fireclay	Drainpipes and fittings.
Vitreous china	High glass content.  Even if its glaze should crack, it will not allow moisture to seep in		Very suitable for sanitary fittings such as toilet bowls, basins and sinks
Porcelain	Similar to vitreous china but is purer.		Special uses, such as for electrical insulators

 

 

Table 2: Features, firing temperatures and uses of ceramics used in building

                                                                                                                     

Bricks

Bricks used in construction are made from:

• clay or shale
• cement/concrete
• sand and lime (calcium silicate).

Methods of brick manufacture

Fired bricks are no longer made by hand.  However, recycled, second-hand, hand made bricks are sometimes available from demolition sites.  They are soft, porous, rather irregular in shape and, if protected from the weather, retain a pleasing warm appearance.

There are, now, two main methods of brick manufacture:

• the dry pressed method
• the plastic or extruded process.

 

 

Dry pressed method

In this method, almost-dry clay powder is pressed into moulds and then fired.  Most dry-pressed bricks have an indentation (called a frog) resulting from the shape of the mould (refer to Figure 1).

Figure 1: A Dry-pressed brick

Plastic or extruded process

With the plastic or extruded process, a soft, moist mix is extruded through a die in the form of a long clay column which is then cut into brick-sized pieces by wires in a frame (refer to Figure 2).  Extruded bricks have a much higher average compressive strength because the proportions between the raw materials are more accurate.

Figure 2: An extruded brick

 

Brick classification

Bricks are graded A, B or C, according to their compressive strength (with grade A being the strongest) and are classified according to type as follows.

Clinkers

• Overburnt and very hard but often distorted in shape; usually unsuitable for regular brickwork; often used for feature walling.

 

Callows

• Underburnt, light in colour, soft, very absorbent; inferior for most structural purpose.

Commons

• General-purpose bricks; hard in texture but often with flaws developed during manufacture.

 

 

Select commons

• Best quality commons, with sharp arises and fairly uniform colour; suitable as a substitute for face bricks.

Face bricks

• Good quality bricks, with smooth or texture faces in a variety of styles and colours.

Sandstock

• Limitation (mechanically-made) or hand-made bricks.

Bricketts

• Small-face bricks, with plain and textured face; often used for fireplaces facings and ornamental feature work.

Firebricks

• Dry-pressed, usually cream in colour, available in a wide range of sizes and shapes; used in furnaces, stoves, fireplaces, and areas of intense heat.

The different types of brick can best be illustrated by looking at appropriate product literature.

With modern methods of applying a surface coating to a compatible colour base, bricks are now available in many colour shades, from black, through reds and yellow to white.

There are also purpose-made bricks which are made in special shapes, eg. bullnose (refer to Figure 3) or squint.

Brick quality and standards

The quality of good bricks is determined by their texture and hardness and their size and shape.

They should have an even, granular texture, be well-fired and free from flaws (eg. face blisters or shrinkage cracks).  Two bricks, when struck together, should give a clear ringing sound.

They should also have regular shaped faces and sharp arises and fall within a standard size range.

Brick sizes:

Metric modular brick    290 ´ 90 ´ 90 mm
Metric standard brick   230 ´ 110 ´ 76 mm

The long face (called the stretcher) of a standard metric brick measures 230 ´ 76 mm, and the short face (called the header) measures 100 ´ 76 mm.

A closer (quarter brick) measures 50 ´ 76 ´ 110 mm (standard metric) and a queen closer (a standard metric brick split lengthways showing a closer face at each end) measures 50 ´ 76 ´ 230 mm (refer to Figure 3).

Figure 3: Variations on standard bricks

 

 

Revison

Undertake the following Questions

• Decide whether the following statements are true or false
• Bricks are produced by two methods, dry pressed and wet pressed (T/F)
• Many dry-pressed bricks gave a surface flaw which is a depression called a frog, (T/F)
• Grade C bricks have the greatest compressive strength (T/F)
• Select commons are the best quality general purpose bricks (T/F)
• Bricks made for structural work are called clinkers or callows. (T/F)
• A good quality brick should give a clear ringing sound when struck against another. (T/F)

 

 

 

 

 

 

• The two drawings below are of different types of standard metric bricks

 

• State the name given to each type
• State the names given to the following features

A              ………………..
B              ………………..
C             ………………..
D             ………………..
E              ………………..

• Supply the missing measurement

E              ………………..
F              ………………..
G             ………………..
H             ………………..
J              ………………..

Laying bricks

Bonding is the way the bricks forming a structure are held together.  Good bonding depends on the chemical bond between the bricks and mortar and on the mechanical bond resulting from how the bricks are laid.

The depth of mortar between bricks is usually 10mm, providing a horizontal joint (called a bed joint) and a vertical joint (called a perpend).

Jointing is the term usually given to the surface finish of the mortar set between bricks.  Such finishes vary according to trends.  Tuck pointing used to be common about the turn of the century but has since faded from popularity.  The most common forms of jointing in use at present are:

• ironed
• flush jointing
• raked jointing (refer to Figure 4).

Figure 4: Examples of different forms of jointing

Many different methods of laying bricks are used, some more effective than others.  Bonding is provided by the way the bricks overlap each other and interlock, and it should:

• distribute the load evenly throughout the mass of brickwork
• tie the mass of brickwork together as an integrated unit
• provide a pleasing arrangement of bricks and joints.

Two types of bonding are illustrated in Figure 5 and Figure 6.  The stack bond (refer to Figure 5), for example, provides little mechanical bond between the bricks (because it creates a vertical downward thrust), whereas with stretcher bond (refer to Figure 6) the load is more evenly distributed throughout the brickwork.

Figure 5: Stack bond

Figure 6: Stretcher bond

Some other bonds, such as the English bond, Flemish bond, colonial bond and garden wall bond, provide an even more effective mechanical integration of the load distribution (refer to Figure 7).

Figure 7: Some types of brick bonds

Accessories for brickwork

There are a number of different accessories which are used with brickwork:

• wall ties
• damp proofing
• anti-termite caps
• ventilators
• lintels
• piers.

Let’s look at how they are used.

Wall ties

Wall ties tie the two walls of a double brick wall together, so that they do not move apart from each other.  (NOTE: In brick veneer construction, wall ties are often referred to as veneer ties.)

The most common type is 4 mm or 3.15 gauge galvanised wire bent to shape, with a kink (or drip) which should be positioned pointing down in the cavity between the two walls to prevent moisture passing along the inside wall (refer to Figure 8).

Wall ties should be spaced no more than 1 m apart and staggered every fourth course in height, with a minimum number of four ties per square metre.  The ties should be at least 6 mm higher on the inner walls than on the outer walls.  If the cavity width is greater than 75 mm, special length ties are used.

Figure 8: A wall tie

 

Damp-proof courses

Damp-proof courses are provided:

• horizontally in walls and on piers to prevent upward seepage of water from the ground or through concrete in contact with the ground
• vertically as vapour barriers to prevent penetration of moisture through a wall
• through walls and across cavities as flashing to control moisture from a roof or parapet or around windows, door heads and sills.

 

 

Termite caps
Termite caps are made of flat galvanised iron, which are placed on top of a DPC material which is then placed on top of a brick pier or timber stump under all timber floor construction.

Termite caps

 

 

 

Ventilators

Ventilators made of terracotta or concrete with wire mesh are set into brickwork to provide under-floor ventilation as close as possible to the underside of the floor, or ventilation into the cavity of double brick walls.

Ventilators

Reinforcement

Reinforcement should be placed in footings and walls where tension stress is likely to occur, because brickwork is weak in tensile strength.  The types of reinforcement available are:

• wire mesh
• welded wire
• fabric mesh
• expanded metal
• steel rods, generally used for vertical reinforcement.

Figure 9: Reinforcement types

Lintels

Lintels are steel bars, steel angles and so on, used over doors, windows, fireplaces or other openings to support the brickwork above (refer to Figure 10).

Figure 10: Lintels

Piers

Piers are brick columns which provide above-ground support for other structural members, usually floors.  They are of two types, attached and isolated.

An attached (or engaged) pier is built attached or bonded to a wall.  It may be used to stiffen or supply lateral support to the wall and carry a superimposed load by providing an additional bearing area.

An isolated (or sleeper) pier is free-standing and usually carries some structural load but it may also be purely decorative (ie non-load-bearing).  In order to maintain stability, attention must be paid to the relationship between the height of the pier and the size of the base dimension.  Tables can be obtained to provide guidance in this respect.

Figure 11: An sub-floor isolated (sleeper) pier
1.5 m max. high and is non-bracing, for over this height
use 350 ´ 350 (core filled plus Y12 rod for bracing)

 

Revision

Undertake the following Questions

• What depth of mortar should be laid between bricks?

…………………………………………………………………………

• What three things should good mechanical bonding provide in a brickwork structure?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………

• Stack bonding is the least effective bonding method of those described.  Why?

……………………………………………………………………………………………………………………………………………………

• What would we do to prevent the two walls of a cavity brick wall from moving away from each other?

……………………………………………………………………………………………………………………………………………………

• Why is reinforcement often needed in brick footings and walls?

……………………………………………………………………………………………………………………………………………………

 

 

• What precaution should be taken when creating openings (such as windows or doors) in a brick wall?

……………………………………………………………………………………………………………………………………………………

• What structural difference is there between the two types of brick piers?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Stone

The use of stone as a building material dates back to the caves and rock shelters of prehistory.  Throughout the ages, different peoples-such as the Britons, Vikings, Egyptians, Chinese, Mayans, Incas, Aztecs, Romans, Greeks, Celts and Tibetans-have appreciated the properties of stone and developed the art of using it.  In many instances, lack of wood or other options forced the use of stone; in other cases, stone was the preferred material because of certain superior properties, such as durability or prestige.

The main rock groups

Rocks, referred to in building as ‘stones’, can be divided into three groups, according to how they are formed in nature:

• igneous rocks
• sedimentary rocks
• metamorphic rocks.

Igneous rocks

Igneous rocks are all formed from molten rock which has cooled and hardened.  For example, rocks such as basalts, volcanic glass and pumice (cooled glassy froth) are formed from volcanic lava.  Rocks such as granite are formed from molten rock that has cooled and hardened underground.

Types of igneous rocks

Granite

Granites and granite-like rocks are hard rocks and are made up of a mosaic of fairly large crystals of various minerals easily visible to the naked eye. Granites are usually light grey or pink in colour but can vary through to quite deep reds.  The trade term ‘granite’ is also used to cover a number of darker rocks including gabbro, a black rock known as ‘black granite’.

Examples are:

• Moruya granite-pale grey (used for the Sydney Harbour Bridge pylons).
• Mudgee granite-deep reds.
• Bathurst granite-reds and pinks, various types from the area around Bathurst.
• Riverina grey-from the Tocumwal area; and pinks from Berrigan.

Trachyte

Trachyte has smaller grains than granite.

Examples are:

• Bowral trachyte-dark olive green or dark grey, occasionally streaked with beautiful veins of glassy crystals and quarried at ‘The Gib’.  Bowral trachyte has been used on a number of Sydney buildings and for the piers of the old Hawkesbury bridge.
• Canoblas trachyte-a very hard and durable stone, it polishes to a soft grey or buff base colour with small pink and black spots and is from Orange (held in great repute by local builders, it makes a good flagging stone and was used as such on the front of most of the older important buildings in Orange).

Basalt

This is a very dark to black, fine-grained igneous rock.  Basalts are often called ‘bluestone’ or ‘blue metal’.  They have been quarried from Orange, Kiama, Dundas, Stirling (near Inverell) and Uralla and used extensively in Melbourne (eg. St Patrick’s Cathedral) and in other parts of Victoria.

 

Dolerite

This is similar to basalt but coarser grained.  It is used extensively as road metal, gravel and aggregate in concrete.

Sedimentary rocks

Sedimentary rocks are most often made up of bits of other rocks, usually as a result of erosion.  For example, layers of mud and sand (the result of other rocks being worn down) become buried deep in the earth and are compressed and hardened to form shale and sandstone. Types of sedimentary rocks are now discussed.

Sandstone

Formed in nature by sand grains which are cemented together, sandstone is a popular building stone when available, as it is fairly easily worked, very attractive in appearance and not very heavy.  Many sandstones, however, are too soft and crumbly to be useful.

Sandstones are porous, allowing dampness to soak through: so, when used as footings, they must have good damp-proof course.  Inadequate or non-existent damp-proofing has resulted in rising damp problems in many old buildings with sandstone footings.

The predominant building stones used around Sydney have been the Sydney and Gosford sandstones.  As these two stones are basically identical, descriptions of Sydney sandstone apply equally to Gosford sandstone.

Sydney sandstone is one of the finest building sandstones in Australia.  Its colour is usually a pale yellowish or buff colour to pinkish or brownish tones, with colour variations within it.  It is easily seen in many road cuttings around the Sydney area, such as the expressways north of Sydney, in the Blue Mountains, and approaches to the Harbour and Gladesville bridges.

Other areas in NSW where sandstone has been quarried include Marulan (used for St Saviour’s Anglican cathedral, Goulburn); Bundanoon, one of the best sandstones in NSW for large buildings, its colour varies from white to pink (used for the base of the soldier’s memorial and town hall in Goulburn and St Michael’s cathedral, Wagga Wagga); Yass; Canberra; Frogshole; Galong; Grong Grong; Milparinka; Mendooran; Newcastle (identical to Sydney sandstone); and Ravensfield.

Limestone

Limestones are sedimentary rocks formed from coral, sea shells and deposits of calcite (the mineral of which shells and coral are made).

Limestone as a building stone is worked and sold under the general name ‘marble’.  However, limestone is also mined extensively for manufacturing lime and cement.

Metamorphic rocks

Metamorphic rocks are formed as a result of changes which have been usually brought about by heat and/or pressure in the earth’s crust.  For example, when shale (a sedimentary rock) is compressed it becomes a metamorphic rock, slate; sandstone, when heated up, perhaps by volcanic lava, turns into quartzite; and limestone becomes marble under pressure.

Slate

Slate is formed by immense pressure in the earth’s crust compressing and altering clay rocks such as shale.  Slate splits easily in layers in one direction, like pages of a book.  Some coloured shales are marketed for paving as ‘slate’, but a true slate is usually grey, greenish grey, bluish or purplish in colour.

Slate is fairly soft and easily scratched, but has a very pleasing appearance when well laid and cared for.  Its softness is obvious when we see how the centre of the tread in the grey slate steps in old buildings are often worn away with use.

The high labour cost of cutting and laying slate roofs led to a decline, but its recent popularity for floors, wall facings and fireplace surrounds has renewed interest in it as a marketable product.

In the early days of the colony of NSW, slate was brought out from Britain as ship’s ballast.  It was then used to roof many early Sydney buildings (some fine old slate roofs are still to be seen around NSW).  Gradually Australian deposits were found and worked-at Chatsbury, Gundagai, Towrang, Black Mountain, Bathurst and Mudgee.

Marble

Limestone, acted on by heat and pressure in the earth’s crust, changes its structure and pattern of colour and becomes marble.  Marble and limestone are both quarried for building stone as ‘marble’, so we will look at them together.  Their colours vary from almost pure white through nearly every possible shade of greys, greens, yellows, reds and blues to black.  They are used for making cement, for ornamental and monumental stones, statues and building stones.

 

Revision

Undertake the following Questions

• State how igneous rocks are formed and name one example of an igneous rock used in building.

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

• State how sedimentary rocks are formed and name one example of a sedimentary rock used in building.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

• State how metamorphic rocks are formed and name one example of a metamorphic rock used in building.

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

Stone classified for building purposes

In the building industry, special terms are used to describe different types of stone.  These terms might indicate the quarry location, the colour, texture, pattern or use of the stone.

 

Trade terms

Some terms, such as the following, have a different meaning in the building industry to their geological meaning.

Granite

This is any medium- or coarse-grained igneous rock used as dimension stone.

Sandstone

Sedimentary rock is made of sand-size grains.  Sandstones with thin, even, regular bedding along which the rock is easily split are termed ‘natural flagstones’.

In NSW sandstone which splits with equal ease in any direction is called ‘freestone’.

Marble

This is any limestone or marble which is able to take a polish and is used decoratively; also includes the metamorphic rock serpentine, termed ‘serpentine marble’.

Dimension stone

This term refers to natural rock used as ‘building stone’, ‘ornamental stone’ and ‘monumental stone’.  It is generally quarried in blocks or slabs and marketed in a variety of sizes and finishes according to customers’ needs.

The main varieties of dimension stone quarried and used in NSW are granite, marble, sandstone and slate.
Although most varieties of dimension stone are widespread in NSW, economically viable deposits are not common.  Suitable sandstone deposits are available fairly close to Sydney, but the other stones are located in isolated areas a long way from major markets.  These localities include: Wombeyan (marble); Yass (limestone); Mudgee (granite); Eugowra (granite); Bowral (trachyte); Bundanoon (sandstone); Tumut (marble); Mulyandry (granite); Middle Arm (slate).

Requirements of dimension stone

These may vary from one project to another but, in general, are as follows:

• It must be able to be extracted in large blocks free from joints and imperfections.
• It must be sound and durable.
• It should be uniform in colour and texture.
• It must have aesthetic appeal (difficult to describe, but such things as colour, pattern, texture and finish are important).
• Stones used for certain purposes must be capable of taking and keeping a polish.  Only ‘granites’ and ‘serpentine marble’ keep a polish when exposed to weather.
• It must be available in quantity so that sufficient reserves exist of fairly uniform stone to meet large orders and future demands for maintenance or restoration work.

Economic outlook

Dimension stone is a moderate to high-cost material.  It is often passed over for cheaper load-bearing materials such as steel and reinforced concrete.

Other dimension stones likely to be in demand include good quality purple and green slate for decorative purposes and good quality white marble, black marble, gabbro and granite.

Construction materials

Construction materials are low-cost minerals and rocks that are extracted in bulk.  They require little processing and are used for construction purposes.  Such materials include the following:

• Coarse aggregate: Crushed and broken stone, prepared road base and gravel.  Usually igneous rocks are used in Queensland and NSW, though sedimentary sandstones have also been used successfully.  The most important deposits are those situated near the larger cities.  Much of the coarse aggregate is used in concrete.
• Fine aggregate: Construction sand which is usually dug from rivers, beaches or dunes, must be clean, with no soil or salt.  It is used mostly for concrete, mortar, sand-lime bricks and fillers.
• Unprocessed materials: These include weathered rock, gravel, soil and loam.  They are used mainly for road-making and site-filling.

General properties of stone

Most natural stones are very good load-bearers and make good footings, walls and pylons.

The amount of thermal expansion is very low for marble and slightly greater for sandstone, slate and granite.  However, allowance should be made for thermal movement.

Some stones, especially igneous rocks (such as granites, trachyte and basalt), are not all porous and therefore do not allow moisture penetration.  Others, like sandstone, can be very porous.

Most natural stones are very durable-a property which can, however, be adversely affected by certain environmental factors.

Factors causing deterioration in stone

Atmospheric pollution

Sulphur chemicals in the air or soil dissolve in rainwater and form weak sulphuric acid which will slowly dissolve marble, limestone, calcareous sandstones and mortars.

Salt

Salts dissolved in water seep into rocks and dry out, forming crystals.  These growing crystals cause pressure in porous rock or in mortar and, as they expand, can cause progressive decay.

Frost

Porous rocks in which water freezes will crack and disintegrate, often very quickly.  However, frost action is not a problem in most parts of Queensland except at heights above 600 metres.

Solubility

Limestone, marble and calcareous sandstone will slowly dissolve in water.

Wetting and drying

Repeated wetting and drying of porous rocks can cause slow surface crumbling and should be guarded against.  (This also weakens mortars.)

Corrosion of metals

As iron and steel rust, they swell.  Where iron or steel rods, bolts or bars are fitted into or between pieces of masonry and allowed to rust, serious damage is caused in stone structures.

Some metals also form salts as they corrode which can be destructive to surrounding stonework.

Vegetation

Most plants, including lichens and mosses, do little damage to stonework, but they do hold moisture, which may be a problem with mortars and porous rocks.  Ivy, however, because of the way its roots penetrate cracks and cavities, can cause serious damage.

Finishes and maintenance of stonework

Surface finishes

Figure 12 gives some idea of the range of tooling that can be done on stone with, usually, a mallet and various chisels.  Today, with mechanisation, sawn and polished faces are used fairly frequently, especially with monumental work.

Figure 12: Some types of surface finishes and tools

Rubble walling

Walls may be built either as:

• random rubble (uncoursed)
• random rubble (coursed)
• square rubble (uncoursed)
• square rubble (built in courses).

Figure 13: Rubble walling

Ashlar walling

Walls may be built either as:

• random ashlar
• ashlar (regular coursed)
• ashlar (irregular coursed).

Figure 14: Ashlar walling

Maintenance

Outside stonework should be cleaned regularly and defective joints raked out and refilled (reappointed) with a sand-lime mortar, not a cement mortar mix.

Methods of cleaning various stones are outlined in Table 3.  Note that caustic soda and soda ash are very damaging and must never be used on any stone.

 

 

 

Stone	Method	Comments
All types	Hydrofluoric acid (5% concentration) Sandblasting, dry Mechanical abrasive tools	Risks damage to adjacent materials.  Fast method, no staining, very dusty.  Sand-blasting and abrasive tools produce a lot of dust
Limestone and marble	Clean water spray, mild detergent, dry and polish with soft cloth	Slow, not suitable for heavy encrustations
Granites	Ammonium bifluoride	Risks damage to adjacent materials

Table 3: Cleaning methods for stone

Preservation

Most stone is fairly durable, so fast decay usually occurs from wrong choice of stone, defects in design, or neglect.  These errors should be corrected before attempting to ‘preserve’ the stone.  For example, salts should not be sealed in, but should be removed by repeated sponging with water.  Get qualified advice before using surface sealers as they can sometimes do more harm than good if not appropriate to the problem.

Alternative materials

Dimension stone faces considerable competition from cheaper materials, in particular exposed aggregate panels and other concrete-based products.  Steel and concrete have virtually replaced dimension stone as a major load-bearing construction material.

Artificial stone

Economic reasons, together with the greater range of architectural finishes available, have brought about a greater use of synthetic and artificial stones, such as the following.

Cast synthetic stone

Pure polyester resin or a mixture of polyester resin and acrylic is moulded into stone-like material which can be cast in single pieces.  In situations where the use of stone would require a number of separate stone sections to be jointed together (eg. in panels or columns) this method offers distinct advantages.  It is also not as hard or as cold as stone and can be worked with wood tools.  It can be produced in a variety of shapes and sizes and is usually used to imitate marble.

Terrazzo

Irregular fragments of marble are set in cement and then rubbed down to a smooth surface (often used as stall partitions in public toilets, older-style sink draining boards and as paving in shopping malls).

Advantages of artificial stone

• It can be moulded to various shapes and sizes.
• Exposed faces can be finished to a described texture and colour.
• It is cheaper than natural rock and it is often used as a facing.
• Moulded or detailed pieces can be produced quickly.

 

Imitation stone

A few materials have been used to imitate stonework.  For example, cement render or plaster grooved and painted to look like ashlar laid stone blocks; pressed metal sheets resembling stonework; or compressed fibrous cement roofing to resemble slate.

 

 

Revision

Undertake the following Questions

• What comprises what is known in the building industry as ‘aggregate’

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

• What is aggregate used for in building?

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• Which rocks are generally porous?

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• What factors in the environment can damage stone?

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