Natural and Manufactured Timbers

Natural timber: two categories, many different properties

Natural timber is wood harvested from trees. Hardwoods come from deciduous trees, which generally lose their leaves in autumn. Softwoods come from coniferous trees, which commonly have needles and cones. Many conifers are evergreen, although larch is an exception.

Hardwoods generally grow more slowly, so supplies tend to be more limited and expensive. Softwoods generally grow faster, are more readily available and cost less. These are useful broad comparisons, but choosing a material requires the properties of the particular timber, not just its category.

Reading timber properties

A timber's strength is its ability to withstand forces without failing. Durability concerns how well it lasts in use. A strong material is not automatically suitable outdoors: exposure to moisture and the need for protection also matter.

Grain is the direction and pattern of the wood fibres. It contributes to both the appearance of timber and its working characteristics. Close, straight grain, darker markings and visible knots help distinguish timbers. Texture describes the character of the surface, while surface finish describes the appearance and quality achieved on it, such as a smooth polished surface.

Absorbency is the ability to take in liquid. It matters both when timber is exposed to moisture and when a finish is applied. Oils can soak into wood, while a sealing finish helps protect the surface. Particularly absorbent surfaces, such as exposed MDF edges, need sealing before painting.

To identify a timber, use several clues together: weight, colour, grain, texture, durability and ease of working. Colour alone is not reliable because a stain can change it. Ease of working includes how readily the material can be cut, shaped and finished.

Recognising useful hardwoods and softwoods

The following examples show why the individual timber matters.

For example, oak's durability and ability to polish well suit furniture that must withstand use while retaining an attractive appearance. Pine offers a lighter, easily worked option where lower cost is important. Cedar shows why an outdoor application does not necessarily require the strongest timber: suitability for exposure is also part of the choice.

Natural timber stock forms

After harvesting, timber is cut at a sawmill and seasoned, meaning dried before use. It may be sold sawn, with a relatively rough surface, or planed, with smoother surfaces. PSE means planed with squared edge.

Natural timber is supplied in standard lengths and sectional forms:

• Plank: a broad, relatively thick rectangular length.
• Board: a broad, relatively thin rectangular length.
• Strip: a narrow rectangular length.
• Square: a length with a square cross-section.
• Dowel: a round rod with a circular cross-section.

These names describe the supplied shape, not the species. Oak and pine, for instance, can both be supplied in different stock forms. Choosing stock close to the required shape reduces the amount that must be removed.

Manufactured boards: fibres, particles or layers

Manufactured boards are made from natural timber that has been broken into fibres or particles, or cut into thin layers, and bonded together. Some use recovered wood materials. They are supplied as sheets, making them useful where a broad panel is needed.

MDF — medium density fibreboard is made from small wood fibres mixed with wax and resin, then heated and compressed. It has no natural grain direction, is easy to work and is a relatively inexpensive, versatile choice for interior furniture. Its absorbency is important: exposed edges readily absorb paint unless sealed first.

Chipboard is made from small wood chips bonded into a dense sheet. Its exposed surface can be unattractive, so it is often covered. Kitchen worktops can use a chipboard core with a decorative melamine surface that provides heat, scratch and water resistance.

Hardboard is a manufactured fibreboard made from pulped or shredded wood compressed together. It is supplied as thin sheet material; a typical thickness is 3.2 mm.

Plywood is made from thin wood veneers glued together. The grain direction in each layer is at 90° to the grain in the next layer. This cross-lamination increases strength and rigidity. The exposed edges show the layers and can be less attractive than the faces. A high-quality face veneer, such as birch, improves the appearance.

Veneered boards have a thin natural-wood covering bonded to a board underneath. The veneer provides the colour and grain of the chosen wood, while the underlying board provides the main structure. Veneering is a way to improve appearance; it does not turn the whole board into solid hardwood.

Standard sheet sizes and thicknesses

Manufactured boards are sold in standard sheet sizes and a choice of thicknesses. Typical sheet dimensions are 2440 mm × 1220 mm; smaller sheets include 1220 mm × 610 mm.

Sheet dimensions describe the length and width; thickness is a separate measurement. A designer must choose both the material and an appropriate stock thickness for the component being made.

Finishes: protection and appearance

A finish can have a functional purpose, such as resisting moisture or wear, and an aesthetic purpose, such as enhancing grain or changing colour. The right finish depends on the material, the product's location and the desired appearance.

• Paint provides colour and protection, usually hiding the natural grain. Matt, silk and gloss finishes are available.
• Wood stain changes or enhances colour while allowing the grain to remain visible. It is normally sealed with varnish.
• Varnish or lacquer provides a protective coating while allowing an attractive wood face to show. Varnish is available in matt and gloss forms and can be applied in layers for durability.
• Oil and wax soak into timber, enhance its appearance and help repel moisture. They are useful when the natural grain is part of the design.
• Preservative treatment helps timber last longer, especially outdoors. Dip treatment protects the surface; pressure-treated timber provides longer-lasting protection for applications such as fencing.

A frequently used timber floor may need a hard-wearing, sealing polyurethane finish, available in oil- or water-based forms and different levels of gloss. A decorative cabinet may instead prioritise the appearance of its grain.

Manufactured boards also need suitable finishes. Plywood with an attractive face veneer can be varnished or lacquered. MDF can be painted or stained, but its exposed edges should be sealed first to prevent excessive absorption. Chipboard can receive a natural-wood veneer for appearance or a melamine covering for both appearance and resistance to everyday wear. The covering and the board underneath perform different jobs, so both matter when selecting the material.

Natural timber

• Hardwood: deciduous trees; generally slower-growing and more expensive.
• Softwood: coniferous trees; generally faster-growing, more available and cheaper.
• Compare strength, grain, surface finish and .