History of Materials and construction

Materials and construction

(History of Materials)

The subject of materials and construction concerns not only the wide range of materials used but also their production and the nature of the building industry. The most common materials are timber, baked and unbaked clay, stone, slate, reeds, grass or straw, glass, concrete, iron and steel. The choice of materials and constructional system sets limits and creates opportunities for architects and builders. Some materials, such as brick, wood and stone, may be very familiar, but it needs careful observation to distinguish particular varieties of timber such as oak or ash, and the differences between the many varieties of stone such as sandstone, limestone and granite.

Eastgate Office Building and Shopping Centre, Harare, Zimbabwe, 1996

(Pearce Partnership)

One of the best ways to recognise these differences is to travel widely, look at the materials used, read guides on the local architecture which identify them and visit geological or local museums which may display local building materials.

Brick:-

Clay is one of the most widely used materials internationally, and bricks have been used for at least 5,000 years, the earliest being sun-dried brick. Burnt brick can be traced back to 2500 BC. Bricks are made by hand or machine and formed by pressing clay into a mould to create an appropriate shape. They are then baked in a clamp or kiln. The illustration shows the hole where clay has been dug to make the bricks. There are bricks laid out on the ground to dry, before being placed in the clamp (made from old bricks) for firing. There are many varieties of fired bricks, which differ widely in colour, texture, form and use. Hand-made clamp-fired bricks can be of uneven texture and colour, some are blackened by over-firing, others pale because of the clay type or underfiring.

Cottage of granite with brick dressings, Newtown Linford, Leicestershire, nineteenth century

The early tenth-century Samanid Mausoleum, Bukhara, Uzbekistan, is an excellent example of the structural and decorative use of baked brick. The mausoleum is in the form of a tapered cube with central dome and four small corner domes. The exterior walls and the external circular corner piers have chequerboard patterns composed of blocks of brickwork. The bricks are in short courses, laid either horizontally or vertically. Bands and panels of decorative brickwork, some consisting of rows of circles, frame the central entrances on each of the four façades and run along the top of the gallery. The gallery has round arched openings framed by colonettes composed either of zigzag or spiral brickwork. The chequerboard wall patterns have diagonally laid bricks contrasting with horizontal coursed squares. The colonettes, arches, spandrels and jali screens of the openings and squinches between the upper wall and the dome are enriched with further brick patterns.

Samanid Mausoleum, Bukhara, Uzbekistan, pre AD 943

Strong, thin Roman bricks were used to create bonding courses at intervals in rubblestone walls or for facing walls with a concrete core. In Britain soft bricks suitable for carving were made from the seventeenth century onwards. Specials, or special bricks, were moulded to virtually any size or shape and used for vaulting, chimneys, string-courses, plinths, copings and the detailing of eaves and openings.

Today, bricks can be of very smooth texture and very hard. Powered machinery is used to mix the clay and remove impurities and large stones, so preventing a rough texture. Extremely strong bricks impervious to moisture called engineering bricks are used for foundations, manholes, damp proof courses at the bottom of walls and civil engineering projects such as viaducts.

The small end of a rectangular brick is called a header and the long side a stretcher. The many different methods for laying or bonding bricks subtly affect the appearance of the wall. The bond is the regular pattern in which the bricks are laid in courses. Two common and structurally strong bonds to look out for are the English and the Flemish: the former has alternate courses of stretchers and headers, the latter has alternating stretchers and headers in each course. Both these bonds create firm walls that are one brick length thick, with headers that run through the thickness of the wall. Stretcher bond consists of courses made up of stretchers only. The wall may be an infill wall, just half a brick thick, called a half brick wall, or it may be a cavity wall. A cavity wall is composed of three elements: separate inner and outer leaves of brickwork and an air space between for insulation and to prevent damp passing between the two leaves. Cavity walls became common in the West from the beginning of the twentieth century. In barns where ventilation is required brickwork may be laid in an openwork honeycomb pattern. If bricks are used as an infill material in a frame structure, called brick nogging, a more imaginative pattern such as herringbone may be used.

 Kensington, London, 1873–5 ( J. J. Stevenson)

From the seventeenth century in England craftsmanship in brick began to reach unprecedented levels. Sometimes the joints between bricks were extremely fine and the decorative aprons or panels under windows, sunken panels over windows and the columns and pilasters were also in brick. To achieve these effects, either bricks were moulded or special fine, soft bricks were used which could be cut and rubbed; this is known as gauged brickwork. Moulded brickwork and fine joints were revived in the nineteenth century for buildings in the Queen Anne revival style.

Mortar:-

Mortar is used to bed various kinds of masonry and has been made from many different materials. Mud, gypsum, lime, cement and volcanic clay or pozzolana have been used, either on their own or with additions such as sand and/or water. Rubblestone walls require large amounts of mortar to bed each layer of stone because of the unevenness of the material. Where stones are very irregular and require large quantities of mortar, galleting, or small stone wedges, are set into the mortar to counteract the rocking or movement of the stones. This technique can be used decoratively as Antonio Gaudí did at the Finca Güell in Barcelona where he added sparkling, coloured glass fragments to the mortar.
The character of stone or brickwork can be affected by the colour of the mortar and its usage. Mortar may be coloured to match the main walling material or made to contrast sharply. In the late eighteenth century colouring the mortar with brick dust and rubbing it down disguised thick joints and uneven-sized bricks. The joint would then be scored and a thin strip of white lime putty inserted to suggest a fine joint. This was called tuck-pointing. In the twentieth century Frank Lloyd Wright wished to emphasise the horizontal in his prairie houses. He used long narrow Chicago bricks and coloured the perpends, or vertical mortar between bricks, to match the brick colour. Jointing may be deeply recessed, project boldly as in ribbon pointing, or be very fine or weathered, that is, angled to throw rain from the joints.

Wall finish:-

The regularity, size and shape of modular building components, together with the type of joint, determine the pattern or texture of the wall and the appearance of scale. The dark and shiny texture of knapped flint, called flushwork alongside stone on the left and brick on the right. Smooth textured walls may be made of any material if the surface is planed or finished, but this can be an expensive process and a common method is to use a render. Render may be made of wet clay, plaster, or a mix of cement, lime and sand. Generally, walls are rendered when they are made of inferior materials such as clay, rubblestone or poor-quality bricks. In Scotland harling has long been a vernacular technique to protect walls from the driving rain. Called roughcast or pebbledash in England, harling is a render in which the final coat of mortar contains pebbles that give a rough texture to the wall.

Knapped flint wall, Lewes Grammar School, Sussex, 1512

Render may be used decoratively with writing, images or patterns created by mixing clay with ash or pigments or using different coloured clays. A particular form of render called stucco was used in Roman and renaissance classical architecture. It was introduced into England by Italian craftworkers in the seventeenth century and can be made from a variety of materials including lime, gypsum or cement, mixed with materials such as marble dust, bone ash, sand, hair and oil. It has been applied to both internal and external walls and it is sometimes pargeted, that is, decorative designs are moulded or incised in the plaster surface. In England from the mid-eighteenth century to the mid-nineteenth century it was fashionable to render and paint the brick walls of classical-style buildings in imitation of fine ashlar stonework. The Orangery, Kew (Sir William Chambers, 1757), for example, was built of brick stuccoed to look like ashlar stonework.

Somerset House, London, 1776–1801 (Sir William Chambers)

In classical buildings the plinth or basement is often made of large, roughly hewn blocks of stone called rustication. Mortar joints are deeply set so that shadows are cast, giving an appearance of massiveness or heaviness even in quite a small building. This can be seen in the basement of Somerset House that has rustication that is vermiculated. An illusion of heavy rustication may also be achieved on a brick or stone wall by the use of sgraffito, where a plaster or stucco render is incised so that the differently coloured coat underneath shows through. At the Schwarzenberg Palace,1545–67, in the old city of Prague, the flat walls of the whole building are covered in sgraffiti to give an appearance of heavy rustication.

Schwarzenberg Palace, old city of Prague, 1545–67

Construction

Construction:-
After identifying the materials, the next step is to find out how the building was constructed by looking at it from both the outside and inside. This is not always easy because it may be concealed or covered by other materials. We may be able to see if a roof is tiled or slated, but not if it is hidden behind a parapet. Inside the building the roof construction is usually masked by a ceiling, so it may be difficult to find out how it is constructed. Visiting building sites or decayed buildings may reveal parts not normally visible, but such places are very dangerous, so supervision and permission are essential.
The method of construction is most important for it ensures that a building stands up, withstands the weather and accommodates the activities for which it is designed. In order to understand why buildings stand up we need to understand how load is distributed and the causes of instability. Thrusts or forces such as the loads of roofs and floors on the walls and supports, wind loads and the nature of the ground upon which the building stands are among the factors that determine its stability. Here we can only discuss some of the most basic issues.

Foundations:-
The design of foundations depends on the nature of the subsoil and the size and load of the building. Foundations distribute the load of a building over a sufficient area of ground to prevent the subsoil spreading and to avoid unequal settlement caused by variations in the load of the building or differences in the subsoil. Some vernacular buildings have posts set directly into holes in the ground and do not have foundations. Historically, some buildings have foundations under the brick footings or courses at the bottom of the wall, and some may have piles or rafts of timber or reinforced concrete. A tall building with an adjoining low-rise block will require two different types of foundation, with a flexible joint between the two that will accommodate the differences in settlement.

Floors:-
In many vernacular structures ground floors consist of soil or clay rammed until firm, and in some cases covered with flagstones or bricks. Problems of cold and damp, particularly in temperate climates, led builders to construct raised timber floors supported on low brick walls or, more cheaply, to create solid ground floors of concrete. Where necessary these latter are protected by a damp-proof membrane of bitumen, asphalt or polythene sheet on top, within or underneath the concrete. Timber floors, whether at ground level or at upper levels, are composed of joists which span the width ofrooms and rest either on corbels, or timber or metal wall plates on or within the wall.
Reinforced concrete floors span wider spaces, are more fire-resistant and can support greater loads than timber floors of similar dimensions. Their design varies from monolithic slabs to closely spaced, hollow, reinforced concrete beams covered with a layer of concrete.

Load-bearing walls:-
Building construction may be divided basically into two types: load-bearing wall construction and frame construction. Load-bearing walls can be of masonry, wooden logs (log cabins) or a number of other materials such as clay, or blocks of ice as in the houses of the Inuit. Even the most humble materials have been used to create buildings with load-bearing walls of great power and beauty. In New Mexico, US, seventeenth-century Spanish missionaries encouraged the building of new churches as part of their campaign to convert the Pueblo Indians. Native Americans built the churches using their traditional material, adobe (sun-dried bricks made of a mixture of clay, straw and water). These large buildings with their clay-plastered walls are impressively austere and monumental. Today, we associate glass with windows and
the thin sheets of plate glass used to clad office buildings, but load-bearing walls have been made of glass bricks, and glass bottles were used to construct the General Store at the Silver Mine, Colorado, US.

Load-bearing panel structures:-
Pre-formed panel construction is like load-bearing wall construction, but each panel is relatively thin and designed to resist its own load and other specified loads. Some panels are of sandwich construction, with steel or timber as the main structural material and a facing of plywood or metal sheeting. Panels may be designed to incorporate openings such as doors and windows. ‘System’ building or the European heavy panel system of reinforced concrete was a totally new approach to building design and production taken up in the UK in the 1950s and 1960s. Mass-produced, prefabricated concrete components or panels were bought as a total building package, often in the form of high-rise flats for local authority estates. The postwar housing crisis and government subsidies encouraged the use of system building and it seemed to offer an economic, efficient and modern way to deal with labour shortages. Moreover, high-rise flats would, it was thought, reduce urban sprawl and improve people’s lives. Some 600 concrete-panel high-rise blocks were built in the UK, but no effective code of practice was developed to control design and construction.9 In 1968 a gas explosion caused the spectacular partial collapse of a block of flats called Ronan Point, Newham, London, and this led to the general discrediting of system building and added to the already widespread mistrust of high-rise flats in the UK.

Membrane structures:-

Thin membranes made of skins, fabric or plastic can be supported by tension and compression structures. A tent or the tipi of native Americans is such a building. The skin or canvas acts as wall and roof to keep out the weather, and the cone of tall wooden poles forms the structural support and is in compression.

House and office of the mine manager, Globe and Phoenix Goldmine, Kwekwe, Zimbabwe, 1895

In other tents the poles have ropes or cables suspended from them to support the cover or membrane and further ropes attached to the poles, called guy or anchor ropes, pegged into the ground to provide resistance to wind. The poles are in compression and the ropes in tension. There are many variations in tent structures between these extremes. Such flexible, lightweight buildings make effective homes for nomadic people and similar principles lie behind some of the most advanced architecture of today, such as the huge Munich Olympic Stadium by Behnisch & Partner with Gunther Grzimek, 1972, and the Schlumberger Petroleum Research Laboratories, Cambridge, Michael Hopkins Architects, 1984 . Alternatively, a reinforced plastic or canvas membrane can be supported by air under pressure or in compression as in inflatable structures. In these the membrane is in tension. Today, there are many sports pavilions that use inflatable structures.

Spanning space:-

An important part of building construction concerns the techniques used to span space, protect buildings from the weather and provide entrances and windows. Much ancient architecture in Egypt, Greece, India and the Far East, including China and Japan, was based on the principle of the post (vertical) and the lintel (horizontal) to span spaces. Trabeated architecture is the term for this relatively stable mode of construction. Horizontal roof or floor beams transmit their load vertically down through the posts that support them.

Schlumberger Petroleum Research Laboratories, Cambridge, 1984 (Michael Hopkins Architects)

Another method of spanning space is to use arches, vaults and domes. A masonry arch is a structure of wedge shaped blocks of brick or stone supporting each other by mutual pressure and able to support a load from above. Arches may be openings in load-bearing walls, they may form an arcade and be supported by columns, piers or pilasters, or they may be freestanding as in ancient Roman aqueducts, triumphal arches or gateways. The most common arches are flat, semicircular, segmental or pointed but there are other more complex shapes such as the ogee, the four-centred arch,

horseshoe and engrailed arch (see glossary, subentries under arch).

Lady Chapel, Ely Cathedral, showing fan vaults, rib vaults and liernes,1321–49

A dome is a convex covering over a circular, square or polygonal space and domes may be hemispherical, semi-elliptical, pointed or onion shaped. A domical vault is a dome subdivided by groins into segments rising direct from a square, circular or polygonal base. Domes can be found in vernacular buildings such as snow houses in Arctic regions as well as more monumental structures such as ancient Buddhist stupas or burial chambers and Roman basilicas and bathing establishments. They are also found in Byzantine churches, mosques and Islamic tombs. In Europe, Christian architecture of the middle ages exploited the vault and during the renaissance it became a challenge to revive the Roman dome for centrally planned churches.Vaults and domes historically have been constructed of stone and brick, but the Romans first used concrete in a dome.

St Basil’s Cathedral, Red Square, Moscow, 1554–60 (Barma and Postnik)

Flying buttresses carried the load of the vaulted roof laterally via an arch over side aisles, ambulatory or chapels to the vertical part of the buttress. This enabled later churches and cathedrals to have tall naves pierced with large clerestory windows. The pinnacles on top of buttresses in gothic churches, or the statuary and balustrades encircling domed roofs, are not there for purely aesthetic reasons. The additional weight that they add to the walls and buttresses helps to stiffen the wall and deflect any lateral thrusts towards a more vertical path and safe transmission to the ground.

Flying buttresses, King Henry VII Chapel, Westminster Abbey, 1503–c.1512

Space frames:-

Developments in steel technology and in computers have led to the application of the space frame to span very large spaces with a minimum of intervening vertical supports. Consisting of a three-dimensional truss framework of connecting bars or tubes and struts, some space frames are curved and others form an extensive horizontal platform. These complex structures are able to resist forces in any direction and so achieve the large, uninterrupted open floor spaces now demanded in warehouses, industrial sheds, supermarkets and sports halls. They were pioneered by designers such as the American R. Buckminster Fuller who developed geodesic domes in timber, plywood, aluminium and prestressed concrete from the late 1940s.

Geodesic dome, Montreal, 1967 (R. Buckminster Fuller)

The largest curved space frame at the time of writing is at the Eden Project, Cornwall, 2001, designed by Nicholas Grimshaw and Partners. The brief, to build the largest greenhouse in the world and hide it in an existing giant pit the size of 35 football pitches, was the brainchild of Tim Smit. His aim was to encourage children to become excited about plants and horticulture and to reach all those people who were uninterested in plants and the environment. The linked biomes, located in disused china clay pits, 60 metres deep, near St Austell, Cornwall, form the largest geodesic conservatories in the world. The biomes cover a tropical zone and a warm temperate zone. The hexagonal structure is fixed to a steel superstructure that is 57 metres high at the highest point. The largest of the hexagons is 11 metres across. Glass would have been far too heavy for such a massive structure and a plastic ETFE (ethylene-tetra-fluoro-ethylene) foil is used to form transparent inflated pillows in each of the hexagons. These are 2 metres deep and have a life of 25 years. On the exterior are abseil points so that the whole building can be cleaned. One of the unexpected hazards discovered on completion was that the crows liked bouncing off the cushions!

Eden Project, Cornwall, 2001 (Nicholas Grimshaw and Land Use Consultants)

Roofs:-
Roofs protect buildings from the weather and may be flat, pitched or curved. Vaults often have a timber truss built over them to protect them from the weather, and flat roofs may consist of a timber, metal or reinforced concreteframed horizontal platform. Pitched roofs are supported on a triangular frame or truss made of wood or metal and can be of many different shapes, some of the most common types being the mono-pitched roof, simple pitched roof, the hipped roof and the mansard roof. Hipped roofs have no gable, as both the ends and the sides slope.

Roof trusses:-
Roof trusses, ubiquitous since the middle ages but originating in Rome, are rigid triangular structures that span space.The lower horizontal beam, or collar, is in tension holding the ends of the diagonals of the truss or rafters in place. The thrust of a truss resting on walls is vertical downwards. However, if the collar is not located low on the truss, there is a tendency for the diagonals or rafters to spring outwards, taking the walls beneath with them. Trusses are usually named after particular features in  their construction. A king post truss has a central vertical member between the apex of the roof and the centre of the tie beam. Queen posts consist of a pair of vertical timbers placed symmetrically on a tie beam. They rise to the side purlins and principal rafters. During the middle ages builders in Britain were keen to make use of the space in timber-trussed roofs, unobstructed by tie beams, and sought ingenious methods of dealing with the lateral thrusts. The hammerbeam truss is one example but there are many other varieties of truss construction.

Hammerbeam truss, St John the Baptist, Badingham, Suffolk, fifteenth century

The roof structure of Chinese timber-framed buildings differed from the UK triangular roof truss. In place of the single collar or horizontal beam there was a system of beams of diminishing length placed vertically above one another running between pairs of posts and separated by short vertical struts. The horizontal roof purlins rested on the struts. This offered flexibility and opportunities for curved as well as straight roof slopes, different internal roof heights and even roofs that finished with a flat top. The basic spatial bay could be varied in numerous ways. The span could be widened by increasing the number of beams and columns or by adding verandah bays, so it was possible to have multiple bays in both directions. A system of brackets or tou-kung made possible deep cantilevering from columns inside and out which, in turn, made possible galleries and especially deep overhanging roofs. The elaborate development of these systems was reserved for monumental buildings and the dwellings of the wealthy.

Chinese roof structure, Wutai Shan, Shanxi, Fogung Si, Tang dynasty, 857

Roof coverings:-
The materials used to cover roofs greatly affect their appearance. Domes may be covered with lead, copper sheeting or tiles. Flat roofs on which water settles need materials with few joints for it to seep into, so large sheets of asphalt, bitumen felt or non-ferrous metals such as lead, copper, zinc or aluminium are used. Pitched roofs may be covered in overlapping flat, modular materials such as slates, stone slates, or tiles of clay or concrete, which are fixed to the roof timbers using wooden pegs or nails. They may be finished at the apex or ridge with plain or decorative clay ridge tiles. In rural areas roofs may be covered in turf or, more commonly, thatch. In the present search for sustainable architecture, grass and other plants have been used on urban roofs.

Methods and processes of construction:-

A look at building sites today shows that an enormous amount of labour is used in construction, even with advanced technology.Women building workers constructing an art gallery by the architect Balkrishna Doshi in India. This use of human labour is a slow process, there may be problems with quality control and in climates such as the UK’s work may be held up for days by bad weather.

Baths, Tenbury Wells, Worcestershire, 1862 ( James Cranston)

In prefabricated buildings the components are manufactured off site and this minimises some of these problems. In many rural American communities barns were made of prefabricated wooden frames. Barn raising was a traditional ceremony, for many strong hands were needed to position and top out the frames. Iron buildings assembled from parts manufactured in a factory included chapels, exhibition buildings, railway sheds and baths.

Health and safety:-
All materials should be thoroughly tested before use in construction, manufactured materials should be made in conditions where workers are protected from dangers associated with the processes or materials. This is not always the case. Knowledge of the working practices in the manufacturing and construction industries and the hazards of certain materials help one appreciate the financial, human and environmental costs involved in the production and use of buildings.

In the nineteenth century when dome-shaped, downdraught kilns were used to fire bricks, pressure on production sometimes meant that workers had to enter the kilns to empty and fill them before they had properly cooled from the previous firing. The dust from asbestos used for its fire-resistant properties has been found to be dangerous to health, as is paint with a lead base. Yet, these materials remain in many older buildings and are still being used in some countries. High alumina cement, used since 1908 because of its quick setting properties, requires very careful supervision and on-site control. It can develop marked constructional weakness when used in humid atmospheres such as swimming pools, where the material ‘converts’ and loses strength. Despite the fact that it was banned in France from 1943 and the risks involved in its use were published in the UK in 1963, it continued to be used there and some roofs collapsed in the early 1970s. The construction industry in the UK today still has a very poor record in terms of industrial injuries, yet there is little attempt to deal with one of the main causes, the widespread use of casual labour.


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