Mortar

Introduction

Mortars are used in residential building in the following areas:

• as a render on masonry

• as a bedding agent in brickwork

• as a bedding agent for ceramic tiles

• as a bedding agent for roof tiles

• as a grout for ceramic tiles

• as a ‘topping’ mortar for concrete.

Learning outcomes

On completion of this unit, you should be able to:

•understand the role of lime and cement in the making of mortars

•define mortar and describe the purpose of mortars in the building industry.

Lime

Lime for building purposes is obtained by burning (calcining) carbonate of lime (limestone). The material is burnt in a kiln for two to three and half days where moisture is driven off leaving rock or quicklime. There are several types of kiln ranging from a simple brick structure to an elaborate rotary type.

Lime is used as a component of mortars in brickwork, masonry and plastering, both in render and setting.

Rotary kiln (hydrated) lime

This is obtained by crushing rock lime in a machine and then spraying it with the exact amount of water required to slake it to a dry powder. This is then conveyed to a separator from which the lime powder is blown off into a storage bin, leaving the impurities behind. It is sold in 25 kg paper bags, with 40 bags per tonne.

Properties of hydrated lime:

• Convenient package size for handling.• Does not deteriorate rapidly when stored.• Ready for immediate use in dry form.• Quantities may be accurately gauged.• It is pure lime.• Hydration is complete, therefore it will not be subject to ‘blows’ in

mortar due to later expansion of lime particles.

Modern additives are now used extensively by ready mix mortar manufacturers to produce a plastic or workable mix.

Portland cement

The process of manufacturing Portland cement was developed and patented in 1824 by an English bricklayer named Joseph Aspin, who named his product Portland cement because it resembled a yellowish building stone being quarried at Portland, England.

Modern industrial developments have led to a Portland cement which is no longer yellowish and therefore no longer resembles Portland stone, at least in colour, although the basic process of manufacture is still the same.

Process of manufacture

There are two methods used to manufacture Portland cement:• the dry method• the wet method.

A description of the two methods follows.

Dry method• Limestone and clay or shale are finely ground.• The two ingredients are carefully proportioned and mixed.• The mixture is fired in a rotating cylindrical kiln. The burning temperature of the kiln is

2600°C– 3000°C. This causes a chemical change and produces a clinker consisting of vastly different chemical compounds to the raw material. (The term ‘calcining’ does not apply to Portland cement manufacture.)

• Gypsum is added to the resultant clinker and the mixture is finely ground again.

Wet methodThis is similar to the dry method except that the initial grinding and mixing is done wet. Samples are tested in the laboratory and blending is carried out as required to produce the correct recipe. The mix is then injected into rotary kilns for burning. After burning the method is similar to the dry process.

Approximately 75 per cent of Portland cement produced in Australia is manufactured by the wet process.

Approximately 11/2 tonnes of limestone and 11/4 tonnes of clay or shale are necessary to produce 1 tonne of cement.

UsesThere are several types of Portland cement which are used as binding agents.

Type GP general purpose Portland cementThis cement is used in concrete for buildings or civil engineering structures such as dams, bridges, roads, tunnels, airport runways, wharves and jetties.It is also used in precast or prestressed concrete products such as building components, both structural and architectural, bricks, blocks paving slabs and garden ornaments.

Type HE high early strength Portland cementThis material has special qualities due to extra fine grinding and/or variation in chemical composition by special selection and blending of raw materials. Setting time and ultimate strength are about the same as normal Portland cement. The cost is slightly increased.

Type LH low heat cementThis material liberates less heat during early setting and hardening than types 1 or 2. It is used therefore in mass concrete to control temperature rises in the concrete. It has somewhat better resistance to some forms of chemical attack than types 1 or 2 because of its chemical composition.

Aluminous cement

Composition and manufacture of this type of cement are considerably different to Portland cement. It is made from a mixture of limestone and bauxite (bauxite is the principal ore of aluminium). It is hydrated alumina.

Aluminous cement can be mixed with Portland cement to accelerate the hydration process and produce a fast rate of strength development.

Sand

Types of sandPit sand—beach or dune sand

This sand is suitable for use in mortar or concrete provided it is collected from above the salt water level or washed to remove any salt (eg Sydney or Botany sands).

Pit sand is generally white or cream. Grey sand is of inferior quality because it contains dirt. Bush pit sand, yellow or brown in colour, shrinks because of its 30 per cent or more clay content and is not recommended for use.

River sand

Usually this is good quality clean sand but it is often made up of particles that are smoother and/or coarser than good pit sand.

Crusher fines

This material is produced as a by-product in crushing rock. The particles are rough and splintery in shape (hungry) and therefore require more paste to produce a workable mix than natural sands.

Grading

A mixture of coarse and fine particles of sand used in mortar for general purposes should pass through a 5 mm mesh sieve. All particles passing this size are termed ‘sand’ (and can be used for mortar) while those retained are termed ‘coarse aggregate’ (and can be used for concrete). Clean sand available for building usually complies with this rule.

Examination

Clean sand will not leave a stain on white cloth or on the hands when rubbed together. Salt may sometimes be detected by tasting water after a small quantity of the sand has been immersed in it. A more reliable method is to use clean water to wash some sand in a small vessel and then add nitrate of silver. Clouding of the solution denotes the presence of salt.

Treatment of poor quality sand

Crushed sandstone is suitable for mortar when free from dust and clay.

Crushed furnace ashes or coke contains corrosive chemicals and is not suitable for use with steel reinforcement. It is, however, good for use in mortar exposed to low furnace heat such as in domestic coppers, incinerators and barbecues.

Substitutes for natural sand

Poor quality sand may be screened or sieved to remove lumps, fine roots and stones. Dust, clay, vegetable matter and salt may be removed by washing the sand under running water in a trough or shallow tank.

Mortar

Mortar may be defined as

a mixture of an aggregate or bulk material and a matrix or binding material.

Sand is the aggregate and lime and cement are the binding materials. These materials are combined to form different types of mortar mixtures in accordance with required strength.

Lime mortar

Lime mortar is a mixture of slaked rock lime or hydrated lime, clean sharp sand and clean water. This is a comparatively soft type of mortar of low strength.

Proportions are one part lime, 21/2 to 4 parts sand by volume and sufficient water to bring the mixture to a workable plastic state.

Mixing on the jobUsing hydrated limePowdered lime may be used directly with measured quantities of sand or it may be soaked for 24 hours in a large drum to ‘fatten’. The lime, sand and water may be mixed by hand on a clean hard surface or may be machine mixed.

Premixed lime mortar This is widely sold by the truck load of 1.25 m3 or in drums for small jobs. It is generally used for brickwork, when available, because of its convenience and the reduced costs in relation to mixing on the site.

Cement mortarCement mortar is a mixture Portland cement, clean sharp sand, and clean water and a small proportion of lime. This makes the strongest type of mortar.

Proportions are one part cement, 3 to 4 parts sand by volume 1/10 part lime together with sufficient water to make a workable plastic mixture.

Mixing is usually done by hand or by machine on the job.

Plasticising agents of many kinds, other than lime, are frequently used to make cement mortar more workable.Cement mortar is best when used before the initial set takes place, normally about one hour after mixing. Mortar re-mixed after the initial set loses some strength and should not, therefore, be re-mixed for use.

‘Compo’ or lime-cement mortorThis medium strength mortar is a mixture of lime, cement, clean sharp sand and clean water. It sets harder than lime mortar but not as hard as cement mortar.

The standard mixture consists of either one part cement, one part rock or hydrated lime and 51/2 to 6 parts sand, or one part cement, 2 parts rock or hydrated lime and 8 to 9 parts sand with sufficient water to make a plastic workable mixture. Quantities of materials should be carefully measured and either hand mixed or machine mixed.

Mortars of all types may be coloured red, brown, black, cream or green by adding mineral oxides in dry powder or liquid forms.

Grout, a thin or liquid mortar (usually cement) used for filling up joints. An excess of water makes the mortar weak. Where strength is required, additional cement is added to the grout. It is preferable to wet the work and allow the water to soak in before grouting.

Bush sand

In some areas (such as Sydney) ‘bush’ sand and cement are mixed to produce a bricklaying mortar, in a ratio of 1:5. Bush sands contain a clayey loam which produces a very workable mix but which is susceptible to shrinkage. For low level residential work this does not pose any real problems.

Additives or admixtures

Proprietary admixtures are available for mortars and usually take the form of air in training agents and are used to make the mix more ‘plastic’ and easier to use.

However, caution should be observed with the use of all admixtures as they are often used contrary to the manufacturers’ recommendations and their effects are often misunderstood by the users.

Summary

Portland cement and lime are generally used on building projects in bagged form and mixed on site. Their main use is on residential projects, including:

• mortar for bricklaying• render for masonry walls• bedding mortar for ceramic tiles and roof tiles• as grouting material.

The strength of mortars varies widely according to the ingredients used. Cement mortars are stronger than lime mortars and are more widely used today.

Portland cement and hydrated lime are factory produced.

Sands are excavated, washed and graded according to local supplies. Water for mortars should be clean and free of organic material. Water gives plasticity to the materials and in the case of cement, it is essential to the hydration process and resulting strength.

Properties of Metals

Introduction

Metals have been used by humans for over 6000 years. The first metals were simply picked up off the ground, but in time people learnt to extract metals from their ores. Nowadays the technology has become quite complex and not only can many metals be extracted from their ores, but the properties of metals can be modified by various types of finishing processes or by mixing with other metals to form alloys. For building purposes, most metals are alloys.

The major base metals used are iron, copper, lead, zinc and aluminium. Metals using iron as their base are called ‘ferrous’ metals while the others are termed ‘nonferrous’. Brass is an important nonferrous metal used in building, being an alloy of the base metal copper.

Glass today is manufactured from the same materials as it was several thousand years ago. Egypt is credited with the earliest glass making technology at least as early as 4000 BC. In Australia commercial glass making began in 1872 in Melbourne with bottle manufacture. In 1903 factories were established and in the 1920s and 1930s products were increased to include window glass. Glass is manufactured commercially from sand (silica), soda and lime. Its characteristics are dependent on the proportions and treatment.

Learning outcomes

On completion of this unit, you should be able to:

• identify and name the metals commonly used in the residential building industry

• understand the effects of the incompatibility of metals

• state the application of the different metals used in building

• list the different types of glass available to the building industry

• state the uses of glass in residential building.

Properties of metal

Metals are substances that can either be hammered (the quality called malleability) or drawn out as wire (the quality called ductility) or melted and formed into shapes in moulds. Most metals can be polished. All metals are, to greater or lesser degrees, conductors of forms of energy such as heat and electricity.

Other characteristics possessed by metals may vary considerably from metal to metal. Some metals (eg stainless steel) have good strength qualities, whereas others (eg tin) have very little strength. All metals, however, will lose strength when repeated force is applied to them—a process known as metal fatigue.

The degree of hardness of a metal will vary according to its natural characteristics (lead and tin, for example, are soft metals; chromium and nickel are hard) and according to the degree to which the metal is worked. When a metal is worked at normal temperatures (by being rolled or forged, for instance) the result will be an increase in its hardness and strength—this it called work hardening.

Properties of metal

Most metals are subject to corrosion, which occurs when the surface of the metal combines with oxygen in the air to form a coat or crust that is no longer metallic (eg rust on iron or steel). Corrosive liquids and gases can actually eat away metals. (We can see the effect of salt air or spray on aluminium.) The process of corrosion is usually greatly speeded up by the action of heat and moisture. Some metals have very low corrosion-resistance, while others have a good degree of corrosion-resistance. Metals with a high degree of corrosion resistance (eg chromium) are often used either as coatings or in alloys with other metals to increase their resistance to corrosive agents.

Forming metals

How metals are formed depends upon the type of metal, the objects being made, and whether parts made of other metals are also incorporated. The following are some of the methods used:

• Casting — where molten metal is poured into moulds and allowed to cool and harden. Rolling hot or cold metal is rolled between heavy rollers to produce various bars, strips, sheets or sections of metal.

• Forging — where hot metal is squeezed into shape, often using mechanical hammers and suitably shaped dies.

• Extrusion — where heated metal is forced through a suitably shaped hole in a hardened steel die to produce continuous solid or hollow sections.

• Drawing wire — or tubes are pulled through tapered dies to reduce the thickness of the metal. Normally the metal is cold and the process lessens its strength.

Joining metalsMetals can be joined by a variety of methods, including the following.

• Mechanical joints: Bolts, screws or rivets are used to join metal components together.

• Soldering and brazing: Most metals can be joined using an alloy which is a mixture of two or more metals that melt at a lower temperature than the melting point of the metals being joined. Soldering usually refers to tin-lead and lead-silver alloys which melt below 300°C.

• Brazing: Gives stronger joints than soldering; however, as it is done at higher temperatures (over 600°C), brazing cannot be used on metals such as lead which have low melting points.

• Welding: Most welding involves a metal being heated to a temperature below its melting point, and the soft metal being hammered together. This traditional blacksmithing method has been replaced by gas welding (using oxyacetylene or propane) and arc welding (using an electric arc struck between the work and a welding rod or a carbon electrode).

• Both brazing and welding involve heating the adjacent metal to extremely high temperatures which allow the metal to flow together and form one continuous unit.

Ferrous metals

Ferrous metals are those metals that contain a large amount of iron. The main types of ferrous metal are:

• cast iron

• wrought iron

• steels.

ManufactureIron ore, as mined, is a combination of iron and oxygen and various other substances. In this country most of the ore is obtained from open-cut mines.

The first step in processing the ore is to reduce it to metallic iron (often called ‘pig iron’), a process carried out in a blast furnace using coke as a fuel and reducing agent. The metallic iron, at this stage, contains a relatively high proportion of carbon (about 4 per cent).

To make steel, the carbon content of the metallic iron must be lowered to less than 1 per cent by an oxidation process in the steelmaking furnace. At the same time, the metal is given whatever special chemical and physical properties may be required by the addition of other metals. The quantities and timing of the additions of carbon and various other elements are carefully controlled to make the wide range of irons and steels that are available.

Effects of added elements

Carbon is the principal hardening element in steel. In plain carbon steels, it is used as the controlling element to regulate physical properties. When the carbon content is increased, hardness and tensile strength are improved but ductility and weldability are reduced (see Figure 7.1).

Figure 7.1: Influence of carbon on the properties of ferrous metals

Effects of added elements

Manganese increases strength and hardness but to a lesser degree than carbon. It also improves the toughness and abrasion resistance of steel.

Chromium increases hardening ability and tensile strength and improves corrosion and abrasion resistance. It is usually associated with nickel additions to form ‘stainless steel’.

By-products an recycling

Blast furnace slag Blast furnace slag is the waste from the smelting process. It is an important by-product which can be used for concrete aggregate, road metal and slag wool for insulation.

Steel scrap This is a major source of metallic iron for steel making. Scrap may either be residue left from the steelmaking process or purchased from discarded or obsolete constructions. About half of the crude steel produced annually in the world will eventually be returned to the steel-making furnaces.

Cast ironCast iron is produced by re-melting pig iron with steel and cast iron scrap. The cast iron has a high carbon content which makes it free-running and, therefore, very suitable for moulding intricate shapes. Cast iron has been used in the past for the decorative iron lace on buildings which is often wrongly called ‘wrought iron’. Cast iron is used for fire grates; for soil waste pipes and ventilating pipes; for drainage gratings and frames; and for baths and basins (with a vitreous enamel finish).

By-products an recycling

Wrought iron

This is a low carbon iron which is excellent for forging but cannot be cast, tempered or welded (by gas or arc). Wrought iron was very popular for decorative finishes (such as balustrades and balcony railings) in the 1950s but has since lost popularity.

Steels

Steels are produced by removing impurities from pig iron and then accurately adjusting the quantities of all the ingredients. Steels are noted for their high strength compared to their production costs, and also for their poor performance in building fires. Ordinary steels do not resist corrosion well, but special steels (eg stainless steel) are produced today with excellent corrosion resistance.

Structural steel

Structural steel products are available in hot rolled sections and cold formed sections.

Hot rolled sections

These are formed while the steel is at elevated temperatures and include the following profiles:

Cold formed sectionsThese are formed while the material is cold as distinct from materials that are shaped or worked while under the effect of heat. Unlike hot rolled sections, cold formed sections have constant thickness.

Cold formed sections may be formed by:

Rolling in a rolling mill (for material up to 20 mm in thickness), the product being what is known as ‘cold rolled sections’ (see Figure 7.2).

Figure 7.2: Rolling in a rolling mill

Cold formed sections

Pressing by means of a press brake (for material up to 20 mm in thickness), the product being what is known as ‘pressed steel sections’ (see Figure 7.3).

Figure 7.3: Pressing with a press brake

Cold formed sections

Pressing by means of a swivel bender (for material up to 30 mm in thickness)—the product being what is known as ‘pressed steel sections’ (see Figure 7.4).

Figure 7.4: Pressing with a swivel bender

Use of structural steels

Pressed steel

Pressed steel is used for:

door and window frames metal trims (such as skirtings) wall panels.

Note: Pressed steel sections are limited to the size of the break press; or, with swivel bending, are able to be produced economically in small quantities.

Alloy steelsAlloy steels contain certain added elements that provide special properties such as ultra high strength or resistance to corrosion or heat.

Stainless steel (containing chromium and nickel) is one such steel alloy which, although much more expensive than mild steel, is being increasingly used in building in a wide variety of applications because of its durability and low maintenance needs (even under extreme conditions of atmospheric pollution, as it has excellent resistance to corrosion).

Stainless steel has outstanding structural advantages because its hardness and toughness allows it to be used in very light sections, thus reducing greatly the weight of finished articles. Even more importantly, it is less affected by extreme heat, such as in a fire.

Except for very simple cutting or drilling on site, all shaping and fitting of stainless steel must be done in suitably equipped factories and workshops.

Stainless steel is also used for sanitary ware (eg sinks and benchtops).

Prevention of corrosion in steel

Upon exposure to the atmosphere ferrous metals combine with oxygen to form a red oxide (ie rust). Rust corrodes the metal and eventually wears it away, leaving behind a red powdery residue. This not only affects the appearance of the metal but substantially reduces its strength.

One way of making steel rust resistant is by applying one of many protective coatings available for steel products. These fall roughly into two groups: metallic coatings and non-metallic coatings. As most require scrupulously clean conditions and special surface preparation of the steel for successful application, factory application of surface coatings is preferable.

Metallic protective coatings

These function by taking advantage of electro-chemical differences between different metals. In adverse atmospheric conditions it is the surface coating that is sacrificed rather than the base metal.

A number of methods are used to apply metallic coatings, such as electroplating, spraying and hot dipping. Metals used to coat the steel include cadmium, zinc, tin, aluminium and copper.

Zinc aluminium alloy applied by the hot dip process has effectively replaced galvanised steel in applications such as roofing because of its greatly increased durability.

Non-metallic coatings

These are available in a wide variety of colours and include:

paints baked epoxy finishes vinyl coatings bituminous coatings vitreous enamel coatings.

Baked epoxy finishes are applied to zinc-aluminium coated steel which is chemically treated to assist bonding. An epoxy primer and then the final colour coat are baked on separately. This type of finish is popular for domestic and commercial roofing and wall cladding for normal conditions.

Non-metallic coatings

In marine and polluted industrial conditions steel can be coated with a tough vinyl which is laminated to the steel substrate. The vinyl coating locks out moisture, making an extremely corrosion-resistant finish.

Vitreous enamel coatings comprise a layer of glass fused to a properly prepared steel base.

Painting should be considered as a complete system that includes surface preparation, pre-treatment to facilitate adhesion, primer, intermediate coat or coats and finish coat. Different types of steel require different pre-treatments and coatings.

Bituminous coatings are based on bituminous resins such as coal tar or asphalt. The bituminous resins perform well underground and in contact with water but do not have good weather durability when exposed to sunlight.

Nonferrous metals

Most nonferrous metals are more costly to produce than ferrous metals. However, they often have much better working properties and resistance to corrosion. The more common nonferrous metals are copper, aluminium, zinc, lead, nickel, tin and cadmium.

Copper

Copper has been in use for at least 10 000 years: nearly 5000 years ago it was being beaten into sheets, pipes, and other building products.

Copper is a pinkish coloured metal and is easily hammered into sheets. It is much more expensive than some alternatives but its extreme resistance to corrosion outweighs this disadvantage in certain applications. Upon exposure to the atmosphere, copper forms a protective copper oxide coating which is light green in colour.

Uses

Its resistance to corrosion has made it popular for use as water pipes and tanks. It also conducts electricity very well, hence its use for electrical wiring. Other uses include roofing, roof plumbing, flashing and damp courses

Brass

Brass is an alloy of copper and zinc, and is an attractive golden colour.

Uses

Brass is used for plumber’s hardware (eg pipe connectors and fittings; taps and outlet spouts, often chrome finished). Screws, nails, grilles, hinges, door locks and latches and chains are often made from brass.

Aluminium

Aluminium is a light-weight metal (approximately one-third the weight of iron) and is silver-white in colour.

Aluminium was introduced as a building material after World War Two in competition with traditional building metals, such as steel and copper. Probably the major characteristic that has helped aluminium gain widespread acceptance in the building industry is its suitability for extrusion production methods. This means that very complicated shapes can be produced economically.

Uses

Aluminium products are extensively used in the building industry—for domestic windows, doors and insect screens; for commercial windows and curtain walls for residential and industrial roofing and rainwater goods; for balustrades and railings and for reflective insulation.

Corrosion resistance

One of the most significant properties of aluminium is its excellent resistance to atmospheric corrosion. On exposure to the atmosphere, a whitish coating of aluminium oxide forms which then protects the surface from further corrosion. The structural integrity is not impaired as a result of this process.

Thus, untreated aluminium can be used for roofing, cladding and so on, but where long-term appearance is important the aluminium should be finished.

Compatibility with other building materials

Corrosion of a metal may be accelerated through contact with another metal of very different electro-chemical properties especially in the presence of an electrically conductive solution, such as sea spray or industrially polluted moisture.

Copper, brass and nickel alloys, all have a large potential difference to aluminium and in a salt solution cause it to rapidly corrode.

Some other building materials are also incompatible with aluminium and direct physical contact with those materials should be avoided or barriers should be used. Table 7.1 broadly indicates the types of barriers suitable for most building construction applications.

Finishes for aluminiumAlthough aluminium is naturally corrosion resistant, various finishes may be applied for aesthetic reasons. These include textured finishes ranging from a fine satin finish (achieved by chemical etching) to a scratch-brushed or hammered finish.

Bright finished aluminium can be achieved mechanically or chemically and results in highly reflective product. To retain the desired appearance, however, the sections should be anodised immediately.

Anodising is an electro-chemical process which greatly increases the thickness of the protective oxide film which would naturally form on the surface, thereby increasing the resistance of the surface to corrosion and damage and enhancing the appearance of the finished product. Film thicknesses can be specified for different applications.

The oxide film may be artificially coloured. Depending upon the process, however, some colours may be subject to ultraviolet deterioration and therefore are only suitable for interior applications.

Paint may be applied to aluminium but factory application is recommended as the process must be carried out in a dust-free environment and the aluminium surfaces must be pre-treated to remove surface contaminations and to provide a key for good adhesion. Powder coating is now widely used as a finish to aluminium in residential building.

Methods of joining aluminium sections

Most physical joining of aluminium elements is achieved with the use of bolts and nuts, screws, nails and rivets. For reasons of compatibility, fasteners are normally aluminium alloy, stainless steel or cadmium-plated steel.

Some modern adhesives such as epoxy and epoxy-PVC types are commonly being used to produce high-strength joints between aluminium and a great variety of other materials.

Welding is also used to join aluminium. If welded assemblies are subsequently anodised, some discolouration in the anodised film occurs across the welded zone.

Zinc

Zinc is a soft, greyish metal which can be hammered or rolled into sheets: such sheets have been used for roofing rainwater goods. Today, zinc’s most important function in the building industry is as a protective coating on steel.

The zinc coating acts first as a barrier to corrosion. However, should the coating be scratched or damaged, exposing the steel, the zinc surrounding the damaged part will itself corrode instead of the steel. Thus by sacrificing the zinc the steel is protected and will not rust until all available zinc is used.

Zinc-aluminium coating

Research has produced a protective coating for steel which combines zinc and aluminium in an alloy. It is easily applied, by hot dipping, and holds to the metal better than zinc galvanising, thus giving much better protection. It is used on sheet steel and cladding.

Lead

Lead is soft and easily worked, but its great density makes it heavy to handle, and thin sheets and pipes will not even support their own weight.

Lead has been used for thousands of years: lead water pipes were used by the Romans, and our word ‘plumber’ comes from the Latin word plumbum meaning lead.

Due to its toxic properties, however, lead is no longer used for water pipes. In the past, it was used for roofing and roof plumbing, but today its use is limited—although in certain roof plumbing situations, its weight and malleability still make it a useful and preferred material.

Uses Lead is used:

• for flashing and damp coursing • for solder (as an alloy with other metals)

• as sheet lead lining for sound proofing.

Nickel

Nickel is a hard, silvery-white, malleable metal. It is resistant to corrosion.

Nickel is used:

• on steel as a base for chromium plating

• as a constituent of stainless steel

• as a nickel alloy (known as ‘Monel metal’).

Tin

Tin is a very costly, soft, weak metal with a low melting point (232°C), but extremely resistant to corrosion.

Uses

Tin is used:

• as a coating on sheet steel (tin plate)

• for solders.

Cadmium

Cadmium is a white, malleable metal that looks like tin.

Uses

Cadmium is used:

• for electroplating steel components (such as screws, latches, handles, locks)

• as plating on brass plumbing fittings, locks, latches, handles and other such fittings.

Chromium

Chromium is well known for its high resistance to corrosion as a plating, and as a constituent of stainless steels and other corrosion-resistant alloys. It is extremely hard and scratch resistant.

Stainless steel

Stainless steel is far harder than mild steel and silvery in appearance. It has wide applications in commercial buildings and has been used extensively for domestic sinks. More recently it has been used for bench tops and as a termite barrier where it takes the form of a very fine mesh which termites cannot penetrate.

Metal frame constructionDomestic and commercial buildings can both be of metal frame construction. This type of construction is versatile, light, strong, time and labour saving, economical, and stable. Walls, roofs and floors can all be constructed this way.

The metal frames made from steel are pre-fabricated in the workshop or before being erected. They can be joined together using rivets, welds, screws or bolts. Figure 7.6: Metal framing for a brick veneer house

Fasteners

The wide range of metal fasteners used to join or fix building materials and components includes:

• nails

• screws

• bolts, nuts and washers

• timber connectors and framing anchors

• masonry anchors.

Screws

Screws are available in a range of sizes, shapes and coatings for use with wood or masonry.

The four most common types of wood screw are:

countersunk head round head raised head coach screws (see Figure 7.8).

Bolts, nuts and washers

Bolts, nuts and washers are normally made of plain steel, alloy steel or a non-ferrous metal, and may have a protective metal coating (such as zinc or cadmium). The bolt heads are usually either dome headed with a square shank; dome headed with a slot; hexagonal or square headed. The nuts may be square or hexagonal and the washers are flat discs with a cental hole. The two most common types of bolt are:

• the coach (or cup head) bolt

• the hexagonal head bolt (see Figure 7.9).

Timber connectors and framing anchors

These are used for joining various timber-framing members. They are made from hot-dipped galvanised steel and are strong and quick to install. Figure 7.10 illustrates some of them, together with their methods of fixing.

Masonry anchors

Masonry anchors are used in concrete or masonry. A strong fixing is provided by the casing expanding into the hole as the nut or bolt is tightened. A masonry anchor may be placed into a mortar joint but is far more effective if placed in the body of the masonry.

The two most common types are:

• the ‘Loxin’

• the ‘Dynabolt’ (see Figure 7.11).

Glass

ManufactureThe art of glass-making is very old and, today, the industry still uses basically the same raw materials as the ancient glass makers.These basic ingredients are:

silica (from sand) soda (sodium carbonate) lime.

With the addition of varying quantities of: dolomite feldspar soldium sulphate cullet (broken glass) decolourising or colouring agents.

The major constituent, silica, is the glass-former while the other minerals act as fluxes and refiners in the melting process. The raw materials are mixed together and melted at approximately 1500°C and then cooled to a workable temperature of about 1000°C, finally hardening at about 500°C.

Glass used in building

Different applications require glass of different thicknesses and properties. The sheet size of the glass area is important: for instance, larger windows require thicker sheets of glass, both for self-support and to resist pressure from wind loads.

Glass is specified by its thickness, method of manufacture and function. Information is readily available from the manufacturers.

Glass used in building

Glass used in building falls into the following categories:

• float glass

• sheet glass

• plate glass

• toughened glass

• heat absorbing glass

• light and heat reflecting glass

• patterned or figured glass

• laminated glass

• wired glass.

Float glass

Floating is the most common modern method for the production of high quality glass for building. It involves a continuous process in which the molten mixture passes to a float bath where it is supported on molten tin. As the ribbon of glass passes through the float bath it is slowly cooled and fed onto rollers (see Figure 7.12).

Sheet glass

This is an older method which produces transparent glass that is not perfectly flat. A ribbon of molten glass is drawn between rollers through a cooling chamber (see Figure 7.13).

Plate glass

This method has been largely superseded by the float glass method. It produces a greater range of thicknesses than the drawn sheet method because the process is continuous. The molten glass is drawn between metal rollers and then between a twin grinder unit which polishes both surfaces simultaneously.

Toughened glass

This is produced from ordinary glass by thermal treatment of the finished product. The resultant surface tension across the sheet causes the glass to fracture into small particles when cut so that once the glass product is so treated it cannot be further modified or cut on site. Toughened glass is three to five times stronger than ordinary glass with regard to sustained loads and impact but the surface is no harder than ordinary glass. This type of glass is commonly used for frameless glass assemblies.

Heat absorbing glass

This is produced by the addition of certain minerals during melting. It significantly reduces solar heat gain and glare in a building by absorbing between 50 and 90 per cent of the infrared rays and 30 and 75 per cent of the visible light rays. As a result, this glass tends to expand and contract more than other types of glass and suitable tolerances must be left in the frame sizes. Heat absorbing glass is available in a small range of tints.

Light and heat reflecting glass

This is produced by coating the glass surface with metallic films. With the use of this glass, solar radiation can be reduced by up to 70 per cent. Frequently this glass forms part of a double-glazing system which protects the coated surface.

Patterned or figured glass

This is produced by passing a ribbon of molten glass between rollers during the cooling process so that a pattern is pressed into the glass.

Laminated glass

Glass layers are bonded together by heat with a polyvinyl butyral interlayer between the glass layers. This technique produces shatterproof and safety glass such as bullet-proof and cyclone-resistant glass, one-way glass and heat and light reflecting glass.

Wired glass

Wired glass incorporates a layer of the fine wire mesh and is an earlier form of safety glass used for industrial glazing, balustrades, shower screens and so on. It is also used as a fire-retardant glass in some situations.

Properties of glass in buildingsThermal performance

Glass expands and contracts on heating and cooling and, to prevent the kind of disasters which happened with early glass curtain-walled skyscrapers, this should be taken into account in the design.

Stresses can be set up in the glass resulting from differences in expansion rates between frames and glazing, especially where frames are metal.

Thermal insulation

Single glazing offers little thermal resistance but the effect of an air gap created by double glazing almost halves the heat loss through a single pane.

The optimum gap is about 20 mm. Heat absorbing and reflecting glasses make an effective contribution to minimising solar heat gain (see Figure 7.14).

Properties of glass in buildings

Acoustic performance

For any degree of sound insulation, double glazing is essential. Sound reduction values vary according to the thickness of the glass and the width of the gap.

Fire resistance

Although non-combustible, ordinary glass breaks and then melts in fires and double glazing offers no significant advantage over single glazing. Certain special glasses offer some degree of fire resistance.

Alternative glass products

Glass fibresGlass fibres are very strong and flexible for their size. They are used in electrical elements and insulators. In addition, their transparent or translucent qualities make them suitable for globes and light shades.

Electrical goodsBecause of its high electrical resistance, glass is frequently used in electrical elements and insulators. In addition, its transparent or translucent qualities make it suitable for globes and light shades.

Glass bricksGlass bricks can form a semi-transparent wall which is self supporting but not structural. This was a popular building material prior to World War Two, at which time production was interrupted, but it is again becoming popular.

Recycled glass productsMuch glass-making involves the recycling of old glass but glass products have been used in alternative ways as building materials. Glass bottles, for instance, have been built into walls. When filled with water, such walls can act as heat storage banks which can be seasonally adjusted.

Summary

MetalsMetals are widely used in the building industry. Some common metals and their applications are:

steel—framing and cladding materials lead—flashings copper—plumbing pipe and fittings and electrical cable brass—tapware and pipe fittings, door hardware zinc—protective coatings aluminium—window and door framing, roof cladding.

Some metals require protective coating to fulfil their service. Steel and aluminium in particular have to be protected from corrosion by the elements and generally most metals should not be allowed to come into contact with each other.

Summary

GlassGlass is manufactured from silica, soda and lime. Different applications require glass of different thicknesses and properties. In particular, larger sheet sizes will require thicker glass to resist pressure from wind loads. Glass is specified by its thickness, method of manufacture and function.

The main use of glass in building is for windows but other functions include lighting and translucent bricks.

Timber

Introduction

On the successful completion of this course, you will have achieved a Statement of Attainment for units:

• BCGBC4006A Select Procure and Store construction materials

• BCGBC4007A Plan building or construction work

• BCGBC4008A Construct on site supervision of a building or construction project

Introduction

Learning outcomes

On the completion of this unit you will be able to:

• Understand the basic characteristics of wood• Determine the factors that affect the durability and

strength of timber• State the main causes of defects in timber• Classify the main types of timber and manufactured

boards according to their use.

IntroductionTree growth

A tree trunk is really a very long cone, not a cylinder (see Figure 2.1 in the guide). The height increase in the trunk or lengthening of a branch is due to growth at the extreme tips.

The trunk does not get longer between branches; it gets thicker to support the weight of the growing tree. Cells under the bark produce this thickening of the trunk.

In cool climates there is a definite seasonal pattern in softwoods and hardwoods, and this is often seen in the growth rings. Counting growth rings can be used as a rough guide to the age of a tree, but the accuracy of this method can be affected by drought, by irregular growth conditions and by where the sample is taken in the trunk.

IntroductionSapwood and Heart wood

Sapwood

Sapwood extends from the growth cells under the bark, (the cambium layer) into the trunk for a short distance. It is made of newly formed wood cells which contain food (including starch) and water.

Heartwood (or truewood) see Figure 2.2.

Heartwood (also often called truewood) extends from the sapwood through towards the centre of the tree. These cells do not contain any food or starch. Heartwood is formed from the gradually dying sapwood. It contains tannins and other materials, making it usually darker and more durable than sapwood.

Introduction

Figure 2.2: Section across a tree trunk, showing its structure

IntroductionSoftwoods and Hardwoods

Timbers are divided into two groups:

Softwoods or non-pored timbersHardwoods or pored timbers.

Non-pored (softwoods) Oregon, Radiata pine, Canada pine, Redwood, Western red cedar, Cypress pine, Queensland pine, Hoop pine, Baltic pine Note: All pines and firs are softwoods

Pored (hardwoods)Tallow wood, Brush box, Black butt, Red gum, Spotted gum, Blue gum, Mountain ash, Stringy bark, Iron bark, Mixed hardwoods, Silky oak, Silver ash, Queensland maple, Red cedar, Pacific maple, (Meranti) Black bean, Blackwood, Ramin,

Note: All eucalypts are hardwoods

Introduction

Soft wood and Hardwood

Study Figure 2.3 and 2.4 detailed illustrations of the Structure of Softwood and Hardwood contained in the guide.

The composition of wood

The chemical composition of wood is very complex. The main constituents are:

Cellulose Lignin.Other substances are also present. One such

group is the extractives.

Introduction

Cellulose

Cellulose is a complex carbohydrate that makes up the cell walls in plant tissue, it is what gives wood its tensile strength. Cellulose is the main component of pulp and paper.

Lignin

Lignin binds wood fibres together, giving wood its structural strength. It is plastic when hot, which is why heated or steam-treated timber is much easier to bend.

IntroductionExtractives

Extractives are substances in wood that can be extracted by being dissolved in solvents. They include sugars and starches in the sap, oils and resins (which give many woods their characteristic smells) and tannins.

Resins are present in many pines, in Douglas fir and Oregon. A high concentration of resins can greatly increase the durability of some woods in two ways:

less moisture absorbentDeters invading organisms.

Answer the questions in your guide

IntroductionResins

Because they flow when heated, resins may exude as sticky drops through surface coatings of stains, paints and other treatments. Kiln drying of such woods reduces this risk.Similarly, rose mahogany and northern silky oak sometimes exude gums which have a harmful effect on finishes, and where it is necessary to apply surface finishes, these timbers should, if affected, be avoided.

Tannins are present in all woods, although some trees contain quite a lot more tannin than the average. When tannin comes into contact with metal, the timber will stain (for fuller details see the section later in this unit on stains in wood).

Complete the questions in the guide

IntroductionConversion into timber

Sawing methods

There are two main sawing methods:live sawingSawing around.

Live sawingLive sawing is the simplest way of sawing a log and involves sawing through and through (see Figure 2.5 in your guide), using large circular saws (band saws).Live sawing is well suited to fast, large-scale production from small logs of good form with few defects. Can result in a large number of seasoning faults (warps, twists, cupping etc).Figure 2.5: Cross-section through ‘live sawn’ log

Introduction

Figure 2.5: Cross-section through ‘live sawn’ log

IntroductionSawing around

Sawing aroundInvolves turning the log during the sawing process so that a number of different cutting directions are obtained. The most common method of sawing around used in Australia is back sawing (see Figure 2.6), but quarter sawing is also used.

Back sawingBack sawing takes longer than live sawing but is more flexible and enables high grade timber to be produced from faulty logs.Figure 2.6: Examples of back sawn and quarter sawn logs

Introduction

Figure 2.6: Examples of back sawn and quarter sawn logs

Introduction

Quarter sawing

Quarter sawing is the only sawing method that reveals the decorative features in some figured timbers (eg Queensland walnut and maple). Some coarse-textured timbers give a harder wearing board when quarter sawn as it reduces the effect of detrimental gum veins in some eucalypts, and quarter sawn timber dries more slowly and is less likely to develop defects and distortions in seasoning.

IntroductionSeasoning

Seasoning is a process of drying out the green timber to a desirable level. This reduces the chance of the timber shrinking, splitting or deforming when used. Drying makes the timber lighter, increases its strength and prevents its deterioration from fungal decay or attack by some insects. Green, sappy wood will not easily take paints, glues and stains, and will exude sap and moisture.

Seasoning is carried out by:stacking the timber and allowing it to dry out naturally in the airdrying it out more quickly in controlled-heat kilnsa combination of air and kiln seasoning.The seasoning process has to be controlled to prevent unacceptable shrinking, splitting or warping and twisting.

Introduction

Stress grading

Timber is stress graded to determine the amount of bending stress it can safely withstand. This allows timber to be used safely and efficiently.

There are two methods for stress grading timber:

Mechanical.Visual grading

Visual grading occurs when experienced graders inspect timber and grade it by eye.

IntroductionMechanical grading

Timber is fed into a machine which applies continuous stress along the length of the timber and then marks it with spray-on coloured dyes (the colour of the dye indicating the stress grade). Sometimes one length of timber will be marked with more than one colour to indicate changes in its strength. The stress grades and colours are shown in Table 2.2 (the higher the number, the greater the stress it can withstand).

Table 2.2: Stress grades and colour codes for timber

Stress grade Colour code, F4red, F5black, F7blue, F8green, F11purple

IntroductionTimber sizes

Timber is sold as either:

Sawn timber (i.e. as it comes, straight from the saw)

Dressed timber sawn timber that has been machine-dressed straight and flat all round.

In most instances standard lengths start at 1800 mm (or 1.8 m) and increase in units of 300 mm up to 6300 mm. Quantities of timber can, however, be produced to special lengths to order.

Dressed timber can be specified as the finished size or, more commonly, as the original sawn size from which it is dressed. A piece of 100 (75 timber, for example, will measure several millimetres less on each face when dressed, due to planing and sanding. The symbol% (or ex) means ‘out of’; thus % 100 (75 means that the piece is dressed from a sawn section of 100 (75.

IntroductionMilled (or dressed) timber

Timber that has been machine-finished to a particular width and thickness or has been machined to a specific shape is called milled or dressed timber.

Milled timbers include the following:

Square and rectangular sectionsTongue and groove boardsWeatherboards and wall panellingMouldings.

Study the sections and mouldings in your guide and answer the questions

IntroductionFeatures of wood

Physical characteristics

The appearance of wood is affected by various physical characteristics:

texturegrainfigureknotshardnesswear.

IntroductionFeatures of wood

Texture

Wood texture is caused by the size and arrangement of the cells, and by variations in the density of the wood. We speak of fine, coarse, even or uneven textures.

Grain

Grain refers to the general direction of growth of the wood tissue, and is shown by the way the fibres separate when a piece of timber is split. We can have, for example, straight, spiral, interlock, curly, wavy or cross grain (see Figure 2.11)

Figure 2.11 Timber showing some types of cross grain

IntroductionFeatures of wood

Figure

Figure refers to the ornamental patterns seen on the dressed surface of the timber and is the result of colours and grain patterns in the wood.

Knots

Knots occur where the branches joined the trunk of the tree. They are harder and darker in colour than the stem wood (see Figure 2.12).

Figure 2.12: Timber knots

Introduction

Features of wood

Hardness

Hardness is how well a material resists being dented. Hardness varies from tree to tree, and also within a tree. End grain is sometimes harder than side grain, and sometimes softer.

Figure 2.13 shows a number of timbers, listed in order of hardness.

IntroductionFeatures of wood

Iron bark HardestGrey boxWhite mahoganyTurpentineBrush boxSilver top ashStringy barkKarriTallow woodJarrahCypress pineRadiata pineDouglas fir (North America)Red cedar Softest

IntroductionFeatures of wood

Wear

Some timbers have a greater resistance to wear than others, a consideration that is particularly relevant to floors. Generally, hardwoods with a relatively high density, with a fine, even texture and small pores are most suitable for industrial or heavy duty floors.

Stains

Some stains occur naturally in wood. Let’s look at some of the most common types and sources of stains in timber.

IntroductionFeatures of wood

Surface stains from moulds

Mould stains develop on sawn timber in the early stages of drying. They do not damage the wood and are removed when the timber is dressed.

Sap or blue stains

Blue stain fungi may attack the sapwood and heartwood of both softwoods and hardwoods—plantation pines are especially susceptible. To stop this, it is important that the tree is seasoned quickly after felling, especially in the warmer months. The strength of the timber is not particularly affected, but the appearance can be streaked and ugly.

IntroductionFeatures of wood

Decay discolour

Pockets or streaks of red-brown or whitish wood may indicate decay. Such wood may be considerably softer than the surrounding wood. This material is often brittle and will usually break if you attempt to prise it out with a knife. This decay is stopped by seasoning and proper maintenance afterwards.

Stains from metals

When the tannins present in wood come into contact with metals a chemical reaction takes place, resulting in the timber becoming stained; for example, the blue-black stain that occurs from contact with iron and steel.

IntroductionFeatures of wood

Staining occurs more easily with green (unseasoned) wood, but if seasoned timber is wet it can still stain. For this reason, external fittings and fasteners should either be galvanised or else not made from metals containing iron or steel.

Iron or steel will, however, cause little or no staining on the following species:

Blackwood, brown alder, brush mahogany, camphorwood, silver quandong, yellow wood.

Copper nails can cause a slight reddish brown stain on some timbers. Aluminium, and galvanised iron and steel do not cause staining, but it is important that the zinc coat on the head of galvanised nails isn’t damaged.

Introduction

Features of wood

Chemical changes within the wood

As the tree grows it can naturally produce colour variations of its own which show up as streaks or blotches. These often increase the decorative value of the timber.

IntroductionFeatures of wood

Stains due to leaching

Intermittent wetting and drying of an uncoated piece of timber can result in colours in the timber migrating, resulting in stains. These can also be carried in the water onto nearby paintwork, brick or concrete, causing unsightly marks. They will eventually fade, or they can be removed with dilute acids such as citric or oxalic acid in a 10% solution in hot water.Species susceptible to such staining include Blackbean, NSW walnut and all eucalypts. Softwoods and most rainforest species are seldom affected.

IntroductionFeatures of wood

Defects in timber

Defects in timber can affect both its appearance and strength. These defects may occur as the wood grows, when the wood is processed or as a result of weathering. The degree of loss of strength is taken into account when the timber is graded.The appearance is not usually important with structural timbers, but very relevant with wood used for finished surfaces and veneers, for example.

Introduction

Features of wood

Defects resulting from the growth process

Generally, defects which result from the growth of the tree are:

sloping grainknotsgum pockets and veinsreaction woodpithcone holes.

IntroductionFeatures of wood

Sloping grain

Figure 2.14: Sloping grain

Knots

Knots can add to the attractiveness of decorative timbers, but affect the strength of structural timbers.

Gum pockets and veins

Cavities in the wood become filled with resin (in softwoods) or gum (in hardwoods). These gum pockets and veins do not usually affect strength but can often affect appearance. Reaction wood Reaction wood is growth that occurs in a tree that is trying to compensate for a lean or bend for example.

IntroductionFeatures of wood

Pith Pith is a soft, furry brown zone, occurring during early tree growth. It is weak and unattractive, and is found especially in young softwoods.

Cone holes

These are holes that form from the pine cone remaining attached to the tree trunk, and the stem of the cone falling when the wood is sawn.

Introduction Features of wood

Defects that occur during felling, seasoning or other conversion processes

Checks

During surface drying, a separation of the layers of wood extending along the grain may occur. These separations are called checks.

Figure 2.17: Checks in timber

Splits

Splits are cracks that extend from one surface to another at the end of a piece of timber.

IntroductionFeatures of wood

Shakes

Shakes are areas of complete or partial separation between layers caused by processes other than drying; by felling, for example.

Figure 2.19: Examples of shakes

Distortion

Growth stresses within the live tree, and stresses during the sawing, drying or storage of timber can result in distortion, or warping, as it is often called (see Figure 2.20).

IntroductionFeatures of wood

Weathering

Weathering results from the combined effects of sunlight and rain. At first, the dark colours fade and light colours darken, but in time all weather-exposed timbers turn grey. This surface grey colour sometimes gets dirty and blotchy because of fungal organisms, but in dry climates or coastal areas of salt spray a lovely silver grey often develops, as is often seen on driftwood.Weathering also causes the grain to stand out and the surface to gradually break down. This surface decay can be quite rapid if dampness is present and rot develops.

Introduction

Timber destroying agents

Wood-inhabiting micro-organisms

These micro-organisms include surface moulds, blue stain fungi, fungi causing wet and dry rot and bacteria. Some (eg blue stain) mar the appearance but not the strength, whereas the fungal rots can completely destroy affected timbers, reducing them to soft, spongy material with no strength.

IntroductionInsect attack

Termites

Often misnamed ‘white ants’, termites prefer moist, dark conditions and are extremely destructive to timber. They eat out the inside of wood, along the grain, leaving only a thin shell of wood.This destruction can be avoided by using termite-resistant timbers, and by isolating timber from the ground, through which termites travel. Efficient chemical termite barriers may also be used to prevent their access. Various poisons are used either to spray affected soils and timbers, or directly on the soil as a barrier to potential invasion or to treat wood before use; however, as many of these chemicals are highly toxic, extreme care should be taken

IntroductionInsect attack

Powder post beetle (Lyctus) This wood-boring beetle infests cut timber. It lives off the starch in the sapwood of pored (hardwood) timbers and, although confined to sapwood, can cause considerable damage. In NSW, before being marketed, most susceptible timbers are required to be treated with a preservative that is toxic to this beetle.

Furniture beetle (Anobium) This borer, which also lives off starches in the wood, chiefly infests the sapwood of seasoned softwoods and can cause extensive damage in untreated wood. The tunnels that are bored out form a honeycomb appearance in the timber, leaving a deposit of fine gritty dust. Affected timber should be treated or removed and destroyed, to prevent spread.

IntroductionInsect attack

Pinhole beetle (Ambrosia)

These beetles attack almost any tree species but only the green timber. The beetle is killed off as the timber dries out with seasoning. Various chemicals are used to prevent or destroy infestation.

Fire damage

Fire causes serious and spectacular damage to timber because of timber’s flammability. While the fire hazard of timber construction is often greatly exaggerated, the fact remains that timber is the only primary structural material that will ignite and burn at high fire temperatures.Attempts are being made to deal with this problem by developing fire-retarding treatments.

IntroductionTimber preservation

Some timbers are naturally durable. Durability can be affected by the chemical make-up of the timber itself, its hardness and the amount of sapwood present in the sample.

For instance, timber with a high concentration of phenolic compounds may be extremely durable, whereas timber with a high carbohydrate content (eg radiata pine) is extremely susceptible to fungal attack. Termites, on the other hand, are less affected by phenolic compounds than by the hardness of the timber. Brush box and turpentine, for example, have high levels of silica compounds which make them difficult for the termites to chew.

Introduction

Timber preservation

The amount of sapwood present can reduce the durability of the timber as a whole. The sapwood of most tree species is susceptible to decay and insect attacks, whereas the heartwood of most Australian species is quite durable.Timbers can be placed into one of four classes for durability; class 1 being the most durable when in contact with the ground. Examples of common timbers in each of the four classes are shown in Table 2.3.

IntroductionTable 2.3: Timber durability classes

Class 1iron barks, grey gum, grey box, cedar, tallow wood, junipers, turpentine, red wood.

Class 2 black butt, spotted gum, forest red, gum white, stringy bark

Class 3 brush box, (class 1 or 2 for termites) brown stringy bark, silvertop ash.

Class 4 yellow carabeen radiata pine white birch douglas firs sassafras hemlocks tulip oak spruces slash pine beeches birches

IntroductionTimber preservation

Timber which is not naturally durable may be impregnated with preservatives to improve its durability. Preventative treatment of timber before sale and use is most effective. Commercial or large-scale treatments available in Australia fall into one of four main categories:

oil-based preservativeswaterborne preservatives – unfixed salts– fixed saltsorganic solvents or light oil solvent preservatives (LOSPs).

IntroductionTimber preservation Oil-based preservatives

The most commonly used oil-based preservative is creosote, a dark brown distillate of coal tar. It is widely used to protect fence posts, transmission line poles and railway sleepers, and can be applied commercially by pressure impregnation or by on-site soaking or brushing. It provides protection against insect attack and decay but has an offensive odour, blackens the timber, and timber so treated cannot be painted or finished. Creosote is also a harmful substance and should not be inhaled or absorbed through the skin.

IntroductionTimber preservation

Waterborne preservatives

Unfixed salts

The waterborne preservatives involving unfixed salts include borax, boric acid and sodium fluoride. These must be diffused or forced commercially throughout the sapwood of susceptible timber and plywood. These preservatives are odourless and non-staining but are not permanent where timber is exposed to water. This treatment is aimed at control of Lyctus (powder post borer).

IntroductionTimber preservationFixed salts

The major waterborne preservative involving fixed salts currently in use in Australia is copper chrome arsenic (CCA). The timber is usually pressure treated and the active components deposited within the timber are permanent.

Timber so treated develops a slight green colour and is protected from borers, termites and decay, even for in-ground applications. After treatment, it is odourless and can be easily painted.

Introduction

Timber preservationFixed salts

CCA compounds are heavy duty preservatives which are not susceptible to leaching. The copper is a fungicide and the arsenic is an insecticide and also limits fungal growth. The chrome acts as a fixing agent, making the copper and arsenic chemicals insoluble.

IntroductionTimber preservationOrganic solvents

The use of organic solvents or light oil solvent preservatives (LOSPs) pressure treatment in which active chemicals are dissolved in clear organic solvents and forced into the timber. A variety of chemicals may be used, which could include pentachlorophenol aldrin, dieldrin, tributyltinoxide and water repellents (waxes) depending on the level of protection required. Timber so treated can be used in exposed situations above ground and, as the original colour of the timber is unchanged, it is suitable for exposed decorative finishes.(For more detailed information, refer to Timber Development Association, TDA Technical Notes TN81/01 ‘Timber Preservation’.)

Introduction

Manufactured boards

A number of different types of manufactured boards are produced for a variety of uses with some advantages over regular timber, and include plywood, particle board, hardboard, solid core board, composite sheet, laminated sections and medium density fibreboard.

Introduction

Manufactured boards

Advantages of manufactured boards

Strength is greatly increased and is more uniform. Solid wood is, on average, 20 times stronger along the grain than across. Thick plywood (over 10 mm thick), on the other hand, is almost equally strong in both directions.Shrinkage is practically eliminated.Boards are available in much larger sizes than can be obtained from a tree trunk.

IntroductionManufactured boards

Advantages of manufactured boards

More economical use can be made of expensive timbers for finishes, while cheaper timbers can be used for the cores.Matching uniform panels can be obtained.Plywood can be formed or bent to make curved surfaces.Fewer splitting problems occur when nailing or screwing.In the case of composite boards, much greater strength-to-weight ratios are obtained and they also have improved insulating qualities.Boards are made to very accurate measurements.

Introduction

Manufactured Plywood

Thick continuous sheets are peeled off rotating logs of wood and then glued together in layers, under pressure. Each layer is laid at right angles to the grain direction of the previous layer (see Figure 2.21), and there is always an odd number of layers. Plywoods are often named according to the number of layers (eg three-ply, five-ply and so on).Decorative timber surfaces on sheets provide attractive finishes for cabinet making, wall panels or wherever a timber finish may be required.

IntroductionManufactured Plywood

Properties Plywood has very good strength for its weight and is very resistant to shear stress. Thin sheets can be readily bent to required curved shapes. Glues and coatings can, when needed, make plywoods moisture resistant so that they can survive weather, wet concrete and marine conditions.UsesIts wide range of uses includes sheet flooring, external and internal wall cladding, sheet roofing underneath other roofing materials, components for structural members, formwork for concrete, decorative panelling fixtures, furniture and wall bracing.

Introduction

Manufactured Plywood

Properties

Standard sheet sizes (for residential construction) are:standard length: 2400, 2100, 1800 mmstandard width: 1200, 900 mm.Other sizes are manufactured for special uses.

IntroductionParticle board

Also called chipboard, this board is made from wood chips glued together under pressure to form solid sheets.

Properties

Particle board has good dimensional stability, and is easy to work with normal carpentry tools, making it ideal for cabinet work. It does not have the same bending and shear strengths as most other timbers and prolonged exposure to moisture will make it swell, causing a reduction in strength and hardness.

IntroductionUses

Particle board is used for tongue and grooved sheets for flooring (both sheets are grooved and a plastic tongue fits into each groove); plain sheets for internal fittings and cabinet making; plain sheets surfaced with formica for tables, bench tops, cupboard sides and doors. Sheets are also made in widths suitable for shelving and edge-stripped with timber along one edge to enhance their appearance.

Standard sizes are:

thickness: ranges from 10–43 mmwidth: 600–1800 mmlength: 1800–4800 mmNote: Standard sizes for particle board flooring are:thickness: 19 mmwidth: 600 and 900 mm.

IntroductionHardboard (masonite)

Wood is pulped and a felt of wood fibres, impregnated with glues, is compressed and cut into sheets of hardboard, also commonly called masonite. The sheets are rough on one side and hard and smooth on the other (unless a decorative texture is pressed into them).TypesHardboards fall into several groups:natural-colour hardboardsprime-coated hardboards (ie natural colour hardboards which have been factory primed with pigmented paint sealers)perforated hardboards (with a regular pattern of holes punched in them and used for ‘peg’ boards, notice boards and sound insulation)pre-finished hardboards (with a variety of finishes and textures).

Introduction

Uses

Hardboards are extensively used in the building industry. Uses include: as wall and ceiling linings; as underlay, to provide an even surface for cork or vinyl titles or sheets; in cabinet making; as facing panels on doors; for decorative feature walls; for partitions and wall bracing.

Introduction

Solid core board (coreboard)

This is made up of a number of solid strips of timber glued together and sandwiched between sheets of cross bonding and face veneering (see Figure 2.23).

Figure 2.23: Coreboard

Composite sheetAlso known as sandwich ply, this has an inner core of insulating material, sheathed with plywood (see Figure 2.24).

Introduction

Solid core board (coreboard)

This is made up of a number of solid strips of timber glued together and sandwiched between sheets of cross bonding and face veneering (see Figure 2.23).

Figure 2.23: Coreboard

Composite sheetAlso known as sandwich ply, this has an inner core of insulating material, sheathed with plywood (see Figure 2.24).

IntroductionAdvantages of glued laminated components

Strength characteristics can be carefully controlled throughout the length of the beam and, depending on the types of timber used, glued laminated beams can be obtained in stress gradings ranging from F8 to F27.

Large structural members can be made from readily available commercial sizes of seasoned timber.The member so formed will be more dimensionally stable and free of surface checks and so on, than the necessarily unseasoned single piece of solid timber.

Design and fixings can be based on the properties of seasoned timber.Material of lower grade can be positioned in the made-up member in locations where it will not affect the overall strength of the member.

IntroductionStructural members with curved, tapered or cambered shapes can be produced readily. Timbers approximately 25–37 mm thick are usually selected, dressed smooth and then placed together with adjacent faces glued and pressed. In this process, the section can be bent to follow desired forms and the resulting shaped components have great stability and structural strength.

They have a good degree of fire resistance because the surface usually chars then resists further burning. They are also useful in corrosive industrial atmospheres.They have a pleasing appearance which has been a great asset in high-quality work, such as public building interiors.

Introduction

Medium density fibreboard

Medium density fibreboard is made of timber chips or fibres which are compressed with glues to form smooth, even-textured boards which are easily worked and stable. They are ideal for cabinet work and their superior finish has made them a viable alternative to timber for domestic mouldings.

IntroductionHealth and safety

A number of timbers contain extractives that can be extremely irritating to skin and mucous tissue, especially when in fine sawdust. Timbers known to contain irritant compounds include crows ash, black bean, silky beech, black wood, western red cedar, miva mahogany, silky oak, cypress-pine, makore and guarea (both imports from Africa).

As a general health and safety consideration, prolonged exposure to dust, both natural and manufactured, is known to cause disease and every precaution, including dust extraction, dust masks and personal cleanliness must be observed.

Answer the questions in your guide