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Building materials

by Jeremy Salmond

Wood was an obvious choice of building material in a country covered in forest – even in the early 2000s it was ubiquitous, using New Zealand’s exotic pine forests. Many houses were topped off with iconic corrugated-iron roofs. But concrete, aluminium and plastic are ousting traditional materials.


Early houses

Māori building materials

Māori used what they found in forests and swamps to make houses and other structures. They wove building materials together as they had no nails. They used timber for posts, ridge poles and outer walls, and rushes, bark or toetoe for thatching, which was attached to battens, often made from mānuka. Slabs of tree ferns were used for walls, and reeds for interior walls.

In the 19th century a few wealthier European settlers brought small prefabricated houses to New Zealand from Britain, or small windows ready to install in a new dwelling, when this could be built. But most people had to rely on local materials. In Wellington local Māori helped settlers build shelters of wood, reed, grass and bark.

Earth houses

In the 1840s and 1850s settlers from Dorset, Cornwall and Devon arriving in Otago, Canterbury, Nelson and New Plymouth constructed cob houses. Layers of mixed clay and straw or grass formed thick, warm walls. A stone wall foundation kept moisture from rising into porous walls. Roofs had wide eaves to keep rain off. Outside walls were plastered.

Sod houses were made from squares of turf laid on edge in layers creating walls. Adobe used the same material as cob to make large blocks. These were sun-dried and laid in walls. Pisé or rammed earth used slightly damp soil rather than clay. Rammed into a timber frame it made a kind of instant concrete.

Wooden houses

As the country was heavily forested, the easiest way to build a house was from wood. New arrivals found wooden houses flimsy, cold, draughty and not very private. Many roofs were covered with overlapping shakes (narrow timber tiles split from blocks), or later shingles (tiles sawn from blocks). Other early roofing included fern fronds, reeds, bark sheets, bitumen-coated fabric, canvas and long boards. From the mid-1800s until about 1915, roofs were pitched between 30 and 45 degrees to ensure that rain would run off – in the south, even steeper roofs were preferred to shed snow.

At first timber was hand-cut using a pit saw. A pit was dug under a felled tree. A long two-man saw reduced the trunk to framing and boards. One man stood on top of the trunk and the other in the pit below. In the late 1850s mass-produced steam-powered machines transformed timber production. These included circular saws, reciprocating (push and pull) saws, and gang saws, which cut multiple boards simultaneously. Increasingly sophisticated machinery produced an astonishing range of wood products.

Sources of timber

By 1900, kauri – the most popular timber for construction – was depleted, and mills turned to other native timbers such as rimu and mataī. In the early 1900s Oregon timber was imported from North America, and can still be found in houses of that period. Large production forests of mainly radiata pine (Pinus radiata) were planted from the 1920s and 1930s. Pine can be used in many different ways for building, including laminating, and its generally clean texture means that it can be worked and finished to a high standard.

Light timber framing

Plentiful wood supplies meant light timber framing was the technique most commonly adopted in New Zealand. A skeleton of closely spaced small timbers (typically 100 by 50 millimetres or 100 by 75 millimetres) was covered with plain weatherboards, each of which overlapped the one below, creating a weatherproof skin. Frames were stiffened with diagonal braces to resist the force of the wind.

Treaty treenails

 

The Waitangi Treaty House was prefabricated in Australia and assembled in New Zealand. All the joints were numbered with Roman numerals cut into the adjoining timbers, and the joints were secured with timber dowels or ‘treenails’.

 

In the 1840s and 1850s iron nails were hand-made, scarce and expensive, so frames were assembled using mechanical joints. These might also be secured with a wooden peg – a trunnel or treenail. The most common jointing method was the mortise and tenon joint, where one piece of wood had a hole in it and the other a projecting piece – some were shaped as dovetails. From the 1860s and 1870s cheaper nails transformed construction, allowing frames to be assembled quickly and boards to be fixed with comparative ease.

Wide rough-sawn boards (called ‘deal’) were attached to inside walls and covered with a form of woven jute called scrim. Wallpaper could be attached over this. In utility rooms, and often on ceilings, plain thin boards with the edges chamfered into V-joints covered large areas. Boards were also tongued and grooved, fitting into one another to create a sealed surface which could be painted or varnished.

In more expensive houses and institutional buildings, plaster walls were preferred. Until the early 1900s this was applied over timber laths – narrow thin wooden strips attached to a timber frame. In the early 1900s metal laths replaced wooden ones in some government buildings. Metal laths were strips punctured and deformed, which created a rough surface to provide a key for the plaster.


Timber

Many timbers (including pine, kauri and kahikatea) can decay, especially if wet. One early treatment to prevent rot involved painting timber with creosote, a preservative made from coal tar. Creosote, almost black with a strong pungent smell, was used until the 1940s. It was replaced by tanalising – a system of pressure treatment with water-borne copper, chrome and arsenic. This extended the life of the timber for decades, even when in contact with soil. Different grades of treated timber are available with different abilities to resist moisture.

Timber dimensions

Construction timber is sawn into standard dimensions, but over time the range of sizes has decreased. The introduction of metric measurement in 1967 and the desire to maximise timber production reduced thicknesses of many timbers.

Traditional dimensions were often exact multiples of inches. A one-inch (25.4 millimetres) board was reduced to 19 millimetres thick, and old sizes such as one-and-three-quarter-inch-thick (32 millimetres) boards, or nine-inch (225 millimetres) framing are no longer available. A piece of framing which was once four by two inches (roughly 100 by 50 millimetres), popularly known as the ‘four-by-two’, was reduced to 90 by 45 millimetres.

New timber uses

In the early 2000s it was difficult to obtain good-quality timber in large dimensions. Large sizes were usually formed by laminating small timber strips. Strips glued and pressed together can form a large, very stable piece of wood. Large frames can be made using laminated timber, sometimes referred to as structural timbers.

Trusses enable large spans to be achieved using quite small timber members. Early trusses were made up from quite large pieces of wood, 75 or 100 millimetres thick, and from 150 to 300 millimetres deep. Modern trusses use much smaller pieces of wood, such as 100 by 60 millimetres, joined with nail plates – flat pieces of steel punched to form a pattern of spikes on one side, which hold adjoining pieces of wood together.

Plasterboard, plywood, chipboard and MDF

New Zealand Wallboards began producing a plasterboard in 1927 in Mt Eden, Auckland. Winstone bought the company in 1930, increasing production fivefold that year to 5 million square feet of plasterboard. It was termed Gibraltar board. Internal wall linings began changing from scrim on deal (wooden boards) to plasterboard.

Dressed for timber

 

Traditionally timber was sold rough sawn or dressed (smoothed), depending on how it was to be used. Today, framing timber is sold as machine gauged – but finished timber is still dressed.

 

Sheet materials can economically use timber as a finishing material, can strengthen framed structures and are also used for temporary works in building. Plywoods use comparatively low grades of timber to form very strong sheets, which can be finished with a visible high-quality surface layer. Plywoods are made up of thin (2 millimetres) sheets of timber peeled from a log and glued and pressed together in layers. Special grades of water-resistant plywood are commonly used to make form work for concrete or for cladding buildings. Decorative plywoods can also be used for furniture and doors.

Other wood-based sheet materials are made from shredded wood combined with resins and pressed into sheets of varying thickness and hardness. These chipboards or particle boards are commonly used for flooring, wall panels, doors and furniture.

MDF (medium-density fibreboard) is another type of panel formed from resin-bonded wood pulp. Its very fine texture allows precise machining. The resulting smooth surface allows a high-quality paint finish.


Stone, bricks and mortar

Stone

Stone or brick were the most common building materials in Britain in the mid-1800s. Loose stones were used as they were (described as ‘rubble’ construction), or were roughly squared to fit against each other. In better-quality buildings, stone from quarries was precisely squared and laid in neat courses – known as ashlar construction.

In New Zealand stone was preferred for important public buildings. Some buildings had corners, window and door openings formed in cut stones, while walls were concrete. Local and imported stone was used in construction of buildings in the 19th century, but it is not a common building material.

Brick

Bricks were made wherever there was clay and sufficient supplies of wood or coal for the kiln. Brick making began very early in New Zealand. Early bricks were hand-made and fired in clamp kilns – a great stack of bricks with firewood between the brick layers. As towns developed, permanent kilns were constructed. Eventually every district had its own local kiln.

Brick and stone withstood fire but not earthquakes. So a technique called brick-veneer construction developed with an exterior wall of brick attached to a timber frame. The most common use of brick in houses was in chimneys. Right through to the 1950s it was customary to have fireplaces in main living rooms and kitchens, and often in bedrooms.

Early plaster

 

Lime was a key component of many interior finishes. The European practice of solid plastering was common in New Zealand in brick and stone buildings. Solid plaster was a very smooth finish formed in three layers, beginning with a lime plaster ‘scratch’ coat, a second ‘bond’ coat, and a final ‘skim’ coat of gypsum plaster.

 

Making lime

Lime was the critical ingredient of mortar used in masonry construction, particularly for making brick chimneys. Limestone (or some other form of calcium carbonate) was burnt in a special kiln to form quicklime. Quicklime was mixed with water (known as slaking), resulting in lime putty, a thick creamy mixture. This was mixed with sand to make mortar, which hardens due to a chemical process called carbonation. As water evaporates, the lime reacts with carbon dioxide in the air, undergoing a chemical change which turns it back into calcium carbonate.

Another type of lime – hydraulic lime – sets partly in a reaction with water. Experiments with this, which began in the 1700s, eventually led to the development of Portland cement. This forms the basis of modern concrete, a much harder and stronger material. Cement was imported from England as early as 1843, and numerous concrete structures were built between 1840 and 1900.

Warkworth’s Wilson brothers produced New Zealand’s first Portland cement in 1883, and by the late 1890s Portland cement manufacturing was well established and competing with imported cement. By 1892 a third of all cement used in public works was locally made, and by 1920 almost all cement was locally produced.


Cement and concrete

Concrete block

Moulded concrete blocks were a cheap alternative to brick masonry and looked a bit like stone. Some were being made in New Zealand in the early 1900s, and a few houses and other buildings utilised them. Firth began the first large-scale production of New Zealand concrete blocks in 1938. Concrete blocks are formed with thin walls, leaving a large cavity in the centre so that reinforcing steel can be placed in the wall. Blocks are made in standard sizes and are joined with a 10-millimetre-thick cement mortar. Concrete blocks proved to be very popular in New Zealand, particularly for industrial buildings, because they allow walls to be rapidly built.

Precast concrete

Entire buildings can be almost all made using concrete frames and floor panels precast in a factory. Very often, precast elements are an important part of the architecture of the building. Precast elements are made in high-quality reusable moulds, with steel reinforcing placed in the mould before pouring the concrete.

Terrazzo

Terrazzo is a special form of precast concrete in which the aggregates are specially selected for their colour and shape, and the cement mix is coloured to obtain a material which is highly decorative. It was widely used in the 20th century for floors in commercial and institutional buildings, as well as for such things as domestic sink benches. Following the casting and curing process, the material is machine-ground to obtain a robust, smooth, fine-grained finish. In the early 2000s terrazzo enjoyed a resurgence of popularity as a high-quality architectural finish.

Tonnes of cement

 

Limestone deposits close to rail links or deep-water ports were ideal for cement manufacture. They were quarried at Whāngārei, Tarakohe in Golden Bay and Milburn in Otago. The names Golden Bay and Milburn became synonymous with cement. In the mid 2000s cement was produced at only two plants – one at Cape Foulwind, near Westport, the other at Portland, near Whāngārei. Their combined output was over 1 million tonnes per annum.

 

Konka board

Konka board was developed in the early 1900s as a lightweight panel system which had some of the virtues of concrete. Concrete for the panels used volcanic pumice as an aggregate, and had a backing of building paper. Panels were about 900 by 900 millimetres, and 50 millimetres thick. They were fixed into timber framing with galvanised steel clips and nails. Joints were covered with hessian (sacking) soaked in wet cement and the whole surface was then roughcast.

Asbestos cement

In the early 1900s asbestos was combined with cement to form thin rigid sheets suitable for cladding and lining for buildings. It could be moulded and it naturally lent itself to use for roofing, including large corrugated sheets known as ‘super six’, with matching spouting and flashings. It was also sold as a large slate for roofing and wall covering. Marketed as a long-lasting lining, it was widely used – especially by home handymen.

In the mid-1970s, asbestos’s link with the lung disease asbestosis was recognised, and it is no longer used in buildings. Where it is found in existing buildings, the law requires it to be professionally removed in strictly controlled conditions. A substitute for asbestos cement is fibre cement, formed with reinforcing fibres of cellulose or glass.


Steel, aluminium, plastics and insulation

Steel

Steel is a mainstay of modern construction. Its great strength in proportion to its dimensions makes it invaluable in multi-storey construction, where control of height is a key factor in the number of floors which can be built. Building height affects the profitability of many projects.

New Zealand is earthquake-prone, and steel frames are particularly useful to achieve earthquake-resistant construction. Steel can also strengthen existing buildings. Steel speeds up construction because steel elements can be prepared in a factory or workshop, complete with protective paint coatings, ready for delivery and assembly at the site.

Pre-cambered floors

 

Floor panels and beams are usually pre-cambered – curving upward in the middle so they will settle at the correct level under their own weight, and that of any concrete poured over panels to form a finished floor.

 

Aluminium

From the 1970s building relied heavily on aluminium. It can be moulded into complex profiles of almost any length. Special aluminium strips are available to join materials, and to form edges, gratings, grilles and trays.

Aluminium window frames transformed the appearance of large buildings, and the methods of constructing them. In domestic buildings aluminium joinery almost completely replaced timber for doors and windows. The material can be pre-coated in a heat-cured paint coating, or it can be electrically anodised to achieve a semi-gloss metallic finish.

High-rise curtain walls

In a curtain wall, aluminium window frames are bolted directly to a high-rise structure to create a sheer wall of glass. The frame itself may be part of the architectural design of the exterior, or it may be concealed behind the glass. Modern curtain walls have to be capable of resisting earthquakes and strong winds – tall buildings flex considerably under these forces.

Plastics

After packaging, the building and construction industry is the second-largest consumer of plastics in New Zealand. There are many forms of plastic, all with particular building applications. Plastics can be moulded into useful shapes such as pipes, valves, gratings, plumbing fixtures, panels, doors, windows, and fittings such as baths.

Build your house out of polystyrene

 

In the 1990s and 2000s a system of building using polystyrene blocks and sheets for cladding became popular in New Zealand. This required a bit of a shift in thinking – for most people polystyrene was a packaging material also used to make cheap chilly bins and children’s surfboards. And its use as a wall cladding has not been without problems – while the material is not to blame (it is an excellent insulator), if it has been poorly installed or designed, moisture that has penetrated or collected on the inside face of the polystyrene cladding cannot escape. Trapped water can lead to rot in the internal timber framing.

 

Plastic’s durability and resistance to chemicals means it is used for carrying fresh water, waste water, and many kinds of chemicals. Its light weight makes handling and installation easy. Many plastic pipes carrying wires and fluids are concealed within walls.

Insulation

Buildings are mainly insulated by inclusion of lightweight materials. Insulation comes in many forms including metallic foils, fibrous blankets and plastics, and combinations of these. Foils include very thin aluminium bonded to heavy paper. Blankets use a wide range of fibres, including wool, polyester, dacron and fibreglass. The most common plastic insulation is expanded urethane (polystyrene) which is supplied in thick sheets or can be placed in liquid form in a structure, where it rapidly expands and fills cavities before drying.


Roofing and glazing

Corrugated iron

Corrugated iron (more correctly, steel) was invented in Britain in the 1820s. Strong and cheap, it rapidly became the characteristic roof for New Zealand buildings, and sometimes walls. It was available as early as 1843. It was imported in large quantities, and often auctioned at ports.

Baby iron

 

A miniature form of corrugated iron was also developed, which was known variously as sparrow or baby iron, and used mainly for walls and small roofs. It has also been widely used as a roof and wall covering for industrial and rural buildings, and in the manufacture of water storage tanks for properties without access to reticulated water.

 

Because steel rusts, sheets were galvanised by dipping them in molten zinc. The zinc coating oxidised in the air, preventing rust. Flashings covering junctions were folded out of plain galvanised sheet, with lead strips attached to the edges which could be pressed down into the shape of the corrugations. Lead-capped nails were hammered through the peaks of corrugations to hold the roof down – the lead caps prevented water entering the nail holes. Lead is poisonous, so it is no longer used on roofs that are used to collect water for consumption. A modern substitute known as flashguard has been developed for these roofs.

Until the 1980s corrugated iron was the most common roofing material, but it has been substantially superseded by aluminium-coated steel products such as Zincalume. It is claimed that these have better corrosion resistance.

Ceramic tiles

 

Most state houses of the 1930s and 1940s were built with concrete or ceramic roofing tiles rather than the more usual corrugated iron. This was to encourage local ceramic tile manufacturing, under a policy known as import substitution. New Zealand had a ceramics industry but not a steel industry.

 

Slates and tiles

The earliest tiles were stone, including slate – a type of stone split into very thin layers. Slate is long lasting, but expensive because of the high labour costs of extraction, shaping and fixing. Originally, much slate was imported from Britain – particularly Wales – but high-quality slate was also found in New Zealand. In the early 2000s slate was imported from China, Spain and the US.

In Australia and New Zealand ‘Marseilles’ tiles (fired clay tiles that interlock) became popular in the early 1900s because of their ease of fixing and comparative lightness. Originally imported from France, these were eventually manufactured in Australia. Later, similar tiles were made from concrete cast in moulds.

The weight of tiles and slate requires more framing than an iron roof. Tiles pressed out of metal became popular – they imitate the look of tiles but do not require the same framing.

Glass

Glass for windows has always been imported into New Zealand, and in the early days, when it was comparatively expensive, it was sold in small panes, about 300 by 250 millimetres. Windows in most houses were divided into multiple squares – if one pane broke, the cost of replacement was not too high. Only very large, expensive houses had sash windows made of a single piece of glass.

Floating glass

 

Until about the mid-1800s imported glass was hand-made. Air was blown into a ball of molten glass, which gradually expanded forming a long cylinder. This was cut and allowed to lie flat. Modern glass is made by pouring the molten glass onto a bed of molten tin to give an almost perfectly flat surface. This is called float glass.

 

Coloured glass

Coloured and patterned ‘fancy’ glass was used in some doors and windows. The earliest examples were formed using ‘flash glass’ – a very thin layer of brightly coloured glass was attached to ordinary clear glass, and decorative patterns could be cut through the coloured layer with grindstones or using acid.

After about 1900 the use of leadlight became popular. This technique had been used in churches for centuries. Coloured glass was cut into shapes and joined with a moulded lead strip (a cane) to make elaborate patterns or pictures.

Modern glass

In the early 2000s glass was used in many forms and applications. It is no longer a fragile and brittle material, and may be given great strength in the manufacturing process – structural glass can be completely self-supporting by using adhesives or stainless steel suspension systems. Glass blocks combine the structural properties of glass with the convenience of masonry construction.

New Zealand energy-saving standards now require the use of double glazing, which significantly reduces the amount of heat lost through glass.


Ironmongery

Ironmongery (or hardware) describes metal components used to connect materials, including moving parts such as door hinges. In the early 2000s most hardware was imported.

Nails

Machine-produced nails were cut from flat plates of metal by machine. Known as type-B nails, these were imported until the end of the 1800s, when wire nails almost completely replaced them. Wire nails are made by feeding steel wire into a machine which, in one operation, holds the wire and cuts it, and forms the head and chisel point – all at the rate of several thousand nails a minute.

Nails work by shear strength, so that the nail resists being pulled from its bed. The shear strength of the nail can also support a very great weight.

Steel nails used for exterior work are galvanised by coating them with a thin covering of zinc, which oxidises, protecting the steel.

Compressed-air-powered nail guns are widely used in the building industry and have sped up construction. They are used to secure framing timbers together, and for nailing timber to other materials such as concrete or steel, using special high-tensile steel nails. Staples are also widely used instead of nails to secure sheet materials.

Screws

Screws are metal pins with a groove shaped like a corkscrew cut into the surface of the shaft. There is an enormous range of screw types, but their purpose is to join materials together. Different kinds of screw are used in timber, metals and plastics.

Wood screws are tapered so that they can penetrate wood without the need to drill a hole – although it is usual to drill first. The tapered shaft means that the screw fits increasingly tightly as it is turned.

Heads of traditional wood screws were originally slotted, with a recessed groove in the surface, but in 1908, a square-drive screw head was invented, followed in the 1930s by the Phillips head screw. Also invented around 1900 was the hexagonal head or Allen Key screw. These screw types have all been imported for use in New Zealand building.

Nuts and bolts

 

There is a range of shapes used for bolt heads and nuts, but the most common is hexagonal. Square-headed bolts are also common. Round-head coach bolts have a hemispherical head, with a square shank beneath which prevents the bolt from turning as the nut is tightened.

 

Bolts

Bolts are similar to machine screws, but are much thicker and longer. Bolts have a shaft with parallel sides and a uniform thread along all or part of the shaft. A bolt needs a hole which is just large enough to allow the shaft to be pushed through, and it relies on a nut to secure the connection by being wound tightly against the material being joined. A circular disk known as a washer spreads the force of the bolt so that the material is not crushed. Through friction it also resists the likelihood that the nut will come undone.

Builders’ hardware

A vast array of specialised components available for building includes brackets, cleats, straps and other metalwork. Special brackets are used to strengthen joints between pieces of timber. Metal strap is nailed over framed walls and roofs to brace them and prevent them moving under load. Heavier metal brackets can be cast into concrete to support timber posts.

Nail plates are flat strips of galvanised steel which have been punched to create multiple small prongs on one side. These are hammered into the surface of adjacent pieces of timber to hold them together. They are widely used in framed structures and in the prefabrication of structural elements such as trusses.


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How to cite this page: Jeremy Salmond, 'Building materials', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/building-materials/print (accessed 17 June 2019)

Story by Jeremy Salmond, published 11 Mar 2010