2.3 ~ Performance characteristics of wood

Different stock forms of timber

Rough sawn, Planned square edge (PSE), Planned all round (PAR), Natural wood Manufactured boards, Mouldings

Rough sawn

Wood that comes directly from seasoning and has rough surfaces produced from initial conversion; rough sawn wood will have nominal sizes rather than accurate finished sizes

PSE

This wood has only one edge that is planed accurately; the rest are rough sawn

PAR

This wood has sides and edges that are planed square, straight and level, leaving a smooth finish and is ready to use

Manufactured board

Man-made and produced in large sheets, typically 1220 mm x 2440 mm

Natural wood

From the tree and is available only at the maximum width of the tree

Mouldings

Available in standard lengths up to aprox 4 meters

Wood is ....

a natural material, can biodegrade if left in landfill

How do fibres grow on the tree?

Along the length of the tree or branch (grain), and these fibres consist of hollow cells supported by lignin resin.

How does wood change with humidity?

Expands and shrinks

When is wood stronger?

Stronger in the direction of the grain and weaker across the grain

When converted to usable pieces, wood is then?

Seasoned to remove the excess moisture (80 - 90 per cent, before use

Why is wood seasoned?

To prevent defects such as twisting, warping, cracks, cupping or bowing; to reduce the time taken to season wood, trees should be felled in the winter when they grow less, have less sap and therefore contain the least moisture

Air seasoning

A traditional, inexpensive method of seasoning that involves stacking the wood under a shelter, protected from the rain; air circulates between the planks to slowly remove the excess moisture

Kiln seasoning

A more expensive but controlled method that is very quick and can take just a few weeks; planks are stacked on to trolleys and placed in the kiln where both temperature and humidity are controlled

Hardwood

A wood from a broadleaf (deciduous tree)

Softwood

A wood from a cone-bearing (coniferous tree)

What does toxicity of wood depend on?

Species, wood dust and sap can be a hazard

Classification of woods

Hardwood, Softwoods, Manufactured boards, Veneers, MF laminates

Hardwoods examples

Oak, Ash, Mahogany, Teak, Birch, Beech

Oak properties

Hard, tough, good weather resistance.Contains tannic acid, which will corrode steel screws or fixings

Oak uses

Furniture, flooring, boat building, cladding, interior and exterior joinery

Ash properties

Tough, open grain pattern - makes it more flexible

Ash uses

Tool handles, ladders, sports goods Laminating

Mahogany properties

Can contain interlocking grain, making it more difficult to work with; rich dark red colour

Mahogany uses

Indoor furniture, shop fittings and cabinets, veneers commonly used on manufactured boards

Teak properties

Hard, tough, straight grain, natural oils resist moisture, acids and alkalis

Teak uses

Outdoor furniture, laboratory benches, traditional boat decks

Birch properties

Hard, straight, close-grained, resists warping

Birch uses

Furniture indoor panelling, veneers used for birch-faced plywood construction

Beech properties

Tough, close grained, hard; available in steamed (white) and unsteamed (pink tinge)

Beech uses

Chairs Chopping boards, tools Steam bent laminated furniture, turned bowls

List examples of softwoods

Pine SpruceDouglas fir, larch, cedar

Pine properties

Straight grain, knotty, can contain resinous knots

Pine uses

Construction work, roof beams and timer frame construction, interior joinery

Spruce properties

Straight grain, resistant to splitting

Spruce uses

Indoor furniture

Douglas fir properties

Straight or slightly wavy grain, few knots, stave. Good resistance to corrosion

Douglas fir uses

Veneers, plywood construction Joinery and construction work

Larch properties

Hard, tough, attractive grain pattern; fades to silver upon exposure outside

Larch uses

garden furniture, cladding, decking, fencing

Cedar properties

Straight grain can corrode ferrous metals due to acidic nature; low density good sound damping; rot- and insect resistant

Cedar uses

exterior cladding sheds, greenhouses, beehives, interior paneling

Examples of manufactured board

Plywood, marine plywood, Aeroply, flexible plywood, chipboard, MDF

Plywood properties

Thin layers of wood are placed and glued at 90 degrees to one another and compressed to form the board. Good strength in all directions, no grain weakness, always an odd number of layers

Plywood uses: structural work, desktops, indoor furniture, floorboards

Marine plywood properties

Similar construction to plywood but is gap- and void-free; uses special water- and boil-proof glue to provide resistance to moisture. Some higher-quality marine plywood is resistant to fungal attack

Marine plywood uses

Boat dashboards, boat lockers, panelling

Aeroply properties

Made from high-quality timber such as birch, available in thin sheets; lightweight, easy to bend around a support frame

Aeroply uses

Gliders Laminated furniture, laser-cut projects, jewellery items

Flexible plywood properties

An odd number of layers glued together with two outer layers made from open-grained timber - allows sheet to flex, bent and glued around a former to achieve a solid shape

Flexible plywood uses

Laminated furniture curved panels

Chipboard properties

Wood chips compressed with a resin such as UF

Chipboard uses

Often veneered or covered with polymer laminate; kitchen worktops and units, shelving, and flat pack furniture

MDF properties

Compressed wood fibres, though UF is added as an additional resin. Has two smooth faces, available in either standard grade or veneered with a layer of timber

MDF uses

Model or mould making; furniture items - bookcases, cabinets and desks

Veneers properties

Thin slices of wood less than 3mm thick

Veneers uses

Decorative coverings for manufactured boards

MF laminates properties

Thin sheets of MF polymer; hard, tough, chemical resistant

MF laminates uses

Decorative coverings for chipboard for kitchen worktops