Timber and timber products - Your Decision · Lumber, LVL). In glue laminated beams timbers approximately 25-37 mm thick are usually selected, dressed smooth and then placed together

Timber and timber products

Introduction Timber material properties and characteristics

Table: Common softwoods and hardwoods used in Australia

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

Hardwoods Tallow wood Brush box

Topic 2.3 Timber CPCCBS6001 Ed 1 1 © New South Wales Technical and Further Education Commission, 2015 (TAFE NSW – WSI)

Blackbutt Red gum

Spotted gum Blue gum

Mountain ash Stringybark

Ironbark Mixed hardwoods

Silky oak Silver ash

Queensland maple Red cedar

Pacific maple (Meranti)

Black bean

Blackwood Rami

Note: All eucalypts are hardwoods

Stress Grading Timber is stress graded to determine the amount of bending stress or loading it can safely

withstand. This allows timber to be used safely and efficiently.

There are two methods for stress grading timber:

• Visual Grading—the traditional method of determining a stress grade, occurs when experienced graders inspect timber and grade it by eye.

• Machine Grading—a machine applies continuous stress along the length of the timber and then marks it with dye (the colour of the dye indicating the stress grade). The most common stress grades and their colours are shown below (the higher the number, the greater the stress it can withstand). Most pine sold in Australia for structural use is now machine stress graded.

(from AEShareNet Timber Plus Toolbox)

2 Topic 2.3 Timber CPCCBS6001 Ed 1 © New South Wales Technical and Further Education Commission, 2015 (TAFE NSW – WSI

Timber 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 all round (with rough surface smoothed away).

Timber sizes are given in the following order and units of measurement:

• length in metres or millimetres

• width in millimetres

• thickness in millimetres

For example: A piece of timber 2100 x 50 x 50, is 2.1m long, 50 mm wide and 50 mm thick.

Standard lengths generally start at 1800 mm (or 1.8 m) and increase in units of 300 mm up

to 6300mm. Large 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 x 75 timber for example, will measure several

millimetres less on each face when dressed, due to planing and sanding. The prefix ‘ex’

means ‘out of’; thus ex 100 x 75 means that the piece is dressed from a sawn section of 100

x 75, and may actually measure 95 x 70 mm.

Milled (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 sections—seasoned timbers are machined to suit a wide range of stock sizes of width and thickness. The timber is usually dressed on all four sides, but may be dressed on particular surfaces as required. If the members are dressed on all four sides, it is said to be ‘dressed all round’ or DAR.

• Tongue and groove floorboards—(T&G) floorboards and wall paneling are machine dressed from seasoned timber to a range of stock widths and thicknesses. A tongue is formed along one edge and a groove along the opposite edge (see figure below). When fitted together, the tongue and groove give great strength to a board (as the joined boards spread the load over a much wider area), and also will exclude draughts, dust and vermin.


Tongue and groove flooring

• Wall cladding and lining—Weatherboards and other timber profiles used for external wall cladding are fixed horizontally to the studs so that they overlap for weatherproofing. Other profiles may be fixed horizontally, vertically or diagonally to studs or noggings. Slimmer profiles are used for internal wall lining and also may be fixed in various directions. Some profiles are illustrated in the figure below.

Examples of timber profiles for wall cladding or lining

• Mouldings—machined to a wide range of stock sizes and shapes and used as finishing pieces in a variety of situations.


Mouldings

Timber 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.

Some timbers are vulnerable to termite attack. Termite destruction can be minimised by

isolating timber from the ground, using physical barriers and chemical treatment of timber

and soil.

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 the table below.

Timber durability classes:

Class 1 - most durable

ironbarks

grey box

tallow wood

turpentine

cedar

grey gum

junipers

redwood

Class 2 blackbutt

forest red gum

spotted gum

white stringybark


Class 3 brushbox (class 1 or 2 for

termites)

brown stringybark

silvertop ash

Class 4 - Least durable

radiata pine

white birch

sassafrass

tulip oak

birches

douglass fir

spruces

beeches

yellow carabeen

slash pine

Timber which is not naturally durable may be impregnated with preservatives to improve its

durability. Preservative treatment of timber before sale and use is most effective.

Commercial or large-scale treatments available in Australia fall into one of five main

categories:

a) oil-based preservative

b) waterborne preservatives—unfixed salts

c) waterborne preservatives—fixed salts

d) organic solvents or light oil solvent preservatives (LOSPs)

e) synthetic pyrethroids

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, particleboard, hardboard, solid

core board, composite sheet, laminated sections and medium density fibreboard (MDF).

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 10mm 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

• 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 can 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

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 10 below), and there is always an odd number of layers. Plywoods are

often named according to the numbers of layers (eg three-ply, five-ply etc).

Grain directions in a sheet of three-ply

Decorative timber surfaces on sheets of plywood provide attractive finishes for cabinet

making, wall panels or whenever an attractive timber finish is required.

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 plywood moisture resistant so that it can survive weather, wet concrete and

marine conditions (e.g. marine ply).

Plywood has a wide range of uses including sheet flooring, external and internal wall

cladding, sheet roofing underneath other roofing materials, components for structural

members, formwork for concrete, decorative panelling, furniture and wall bracing.

Standard sheet sizes (for residential construction) are:

• Standard length: 2400, 2100, 1800mm

• Standard width: 1200, 900mm

Other sizes are manufactured for special uses.

Particleboard Also called chipboard, this board is made from wood chips glued together under pressure to

form solid sheets.

Particleboard 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.


Particleboard 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 plastic laminate (such as Formica) for tables, benchtops,

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 10-43mm

• Width 600-1800mm

• Length 1800-4800mm

Note: Standard sizes for particleboard flooring are:

• Thickness: 19mm

• Width 600 and 900mm

Particleboard

Hardboard (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 during

manufacturing).

Hardboards fall into several groups:

• Natural-colour hardboards

• Prime-coated hardboards (i.e. 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)

• Prefinished hardboards (with a variety of finishes and textures)

Hardboards are extensively used in the building industry. Uses include as a wall and ceiling

lining; as an underlay for cork and vinyl tiles or sheets (to provide an even surface); in

cabinet making as face panels on doors; for decorative feature walls; for partitions and wall

bracing. With the use of appropriate glues hardboard can also be used externally for

weatherboards.


Solid 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 12 below)

Coreboard

Medium Density Fibreboard (MDF) Medium density fibreboard, MDF 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.

Manufactured Structural Timber Products

Laminated Sections (e.g. Glulam, LVL) These are structural members (such as beams, planks and boards) of long length and large

cross-section made by gluing together medium lengths of seasoned, small cross-section

timber (glue laminated beams see figure) or layers of timber veneers (Laminated Veneer

Lumber, LVL). In glue laminated beams timbers approximately 25-37 mm thick are usually

selected, dressed smooth and then placed together with adjacent faces glued and pressed.

The use of laminations is necessary due to difficulties in obtaining solid timber in large cross-

section which is structurally sound due to depleting timber resources. There is also a

considerable time delay and energy usage in seasoning large timber sections.

Advantages of glue laminated components: • Strength characteristics can be carefully controlled throughout the length of the

beam and, depending on the types of timber used, glue laminated beams can be obtained in stress grading ranging from F8 to F27

• Large structural members can be made from readily available commercial sizes of seasoned timber

• Laminated beams will be more dimensionally stable and free of surface checks and faults than the necessarily unseasoned single piece of solid timber

• Design and fixing 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


• Structural members with curved, tapered or cambered shapes can be produced

readily. 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

• Depending on the type and class of timber used they can produce an attractive appearance for high-quality work, such as public building interiors

Laminated timber beam


Examples of the use of timber

Timber as a structural material Timber in sustainable building

design


Timber for flooring and furniture Timber windows and stairs

Timber joinery Timber visual qualities

Timber colour, grain and features are important aesthetic qualities for selection of timber

particularly for interior applications.


Additional reading: This topic has been an introduction to timber in residential construction. To gain a more

detailed knowledge of timber and its properties and practical use, you should now read the

Timber in detail reading material provided. If you would like to know more about the

practicalities of the use of timber, go to:

• http://www.timber.net.au/

• http://www.woodsolutions.com.au/

• http://www.tdansw.asn.au/ (Timber Development Association)

Collect interesting pieces of information about the use of timber and add them to your

resource and reference collection.


http://www.timber.net.au/

http://www.woodsolutions.com.au/

http://www.tdansw.asn.au/

Documents

Timber and timber products - Your Decision · Lumber, LVL). In glue laminated beams timbers approximately 25-37 mm thick are usually selected, dressed smooth and then placed together