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Timber terms and definitions

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

C

Colour
The colour of dry heartwood; this can vary considerably within species.

D

Density
The weight per unit volume, in kilograms per cubic metre (kg/m3), of wood seasoned to a moisture content of 12%.
Deposits
Chemical substances filling the vessels in heartwood, often white or yellow in colour.
Durability
The natural ability of the heartwood to resist decay (as a result of fungal attack) in high risk conditions (for example, low ventilation or high moisture). A four-class system is used: Durability Class 1 being most durable and Durability Class 4 least durable.

E

Earlywood / latewood
Seasonal growth patterns produce growth rings in some species. Earlywood, formed at the start of the growth cycle, is lighter in colour and lower in density than latewood.

F

Figure
The natural pattern on dressed wood surfaces associated with contrasts in colour, grain or texture.
Finishing
Relates to the suitability of the timber for staining, waxing, painting, and other finishing.
Frothing test
Positive if a persistent lather or froth is produced when a few fine shavings are vigorously shaken up in a test tube of water.

G

Gluing
Ability of the timber to be bonded with adhesives.
Grain
The orientation of the wood elements relative to the main axis of the piece of timber.

H

Hardness
Resistance of the wood to indentation and its relative ease of working with hand tools. Timbers are classified into six hardness categories: 1, very hard; 2, hard; 3, moderately hard; 4, firm; 5, soft; 6, very soft.
Hardwood / softwood
Regardless of weight or hardness, 'hardwoods', e.g. red cedar, are technically defined as those woods having vessels (pores), while 'softwoods', e.g. hoop pine, are defined as those not having vessels.

I

Intercellular canals
Canals usually running in a radial direction, often in conjunction with rays. On rare occasions they run longitudinally.

L

Lyctine susceptibility
Indicates the susceptibility of untreated sapwood (of hardwood species) to attack by the powderpost beetle (Lyctus brunneus).

M

Machining
Behaviour of the timber when planed, sawn, drilled and worked by hand or with machine tools.

P

Parenchyma

Specialised thin walled cells, often called 'soft tissue' which, together with the rays, form the food storage system of the tree. Parenchyma is often lighter in colour than the rest of the wood. It may be: 'sparse,' where isolated cells are adjacent to vessels and are difficult to see; 'diffuse' where cells are scattered irregularly throughout the cross-section, or present in the following characteristic patterns visible on the traverse section.

  1. 'Apotracheal' - independent of the vessels.
    1. Reticulate - fine bands of cells forming a net-like or ladder rung pattern with rays.
    2. Banded - lines more or less parallel to the growth ring; wide or narrow and regularly or irregularly spaced.
    3. Terminal - a band occurring at the end of a growth ring
  2. 'Paratracheal' - associated with the vessels.
    1. Vasicentric - complete circles around the vessels.
    2. Aliform - in circles around the vessels but with wing-like extensions.
    3. Confluent - the wing-like extensions run together linking the vessels.
Planes of reference
Radial: A longitudinal plane along the radius of the stem. Tangential: A longitudinal plane at right angles to the radius of the stem. Transverse (cross section): A plane crossing the stem axis at right angles.

R

Rays
Ribbons of cells aligned radially in the tree.
Resin canals
Ducts found in some conifers (softwoods); occurring both longitudinally and radially in the tree.
Ring porous
Vessels concentrated in concentric rings about the tree pith.
Ripple-marks
Rays aligned in ranks when viewed without a lens on a smooth tangential surface; resembling ripples of waves in a tiered arrangement.

S

Sapwood
The zone of lighter coloured wood outside the heartwood, adjacent to the bark. In the growing tree these are the living cells that conduct water and mineral salts from the roots to the crown.
Seasoning
Drying timber to a moisture content range appropriate to the conditions and purposes for which it is to be used.
Shrinkage
A change in dimensions occurring as the timber dries from a 'green' to a seasoned condition. Shrinkage can occur in three directions: radial, tangential and longitudinal.
Strength groups
Timbers with similar strength properties are grouped for structural design purposes. All timbers are therefore classified into strength groups with a seven-class grouping (S1 to S7) for unseasoned timber and an eight-class grouping (SD1 to SD8) for seasoned timber. Class 1 indicates highest strength in each case. Where complete mechanical data is not available, provisional assessments have been made and are shown in brackets e.g. (S2), (SD2). See Australian/New Zealand Standard AS/NZS 2878-2000, 'Timber - Classification into Strength Groups', for further information.
Stress grade
Stress grading is a system for grouping timber in relation to a set of design properties so that design capabilities can be matched with end-use. A stress grade has an associated suite of design properties including allowable bending stress and characteristic short duration, average modulus of elasticity parallel to the grain. A stress grade of, for example, F8 indicates that for such a grade of material, the characteristic design stress in bending is approximately 25 megapascals (MPa). Visual stress grading is done in accordance with AS 2082-2000 'Visually stress-graded hardwood for structural purposes.'

T

Texture
The relative size, proportion and distribution of the wood elements that produce coarse, medium or fine texture, either uniform or non-uniform.
Tyloses
Ingrowths into the vessel cavity in heartwood; they usually glisten on the transverse section.

U

Unit shrinkage
Percentage of change in dimensions with each one percent change in moisture content (below about 25% moisture content).

V

Vessels (pores)
Relatively large diameter cells aligned longitudinally in hardwoods.

References

Boland DJ, Brooker MIH, Chippendale GM, Hall N, Hyland BPM, Johnston RD, Kleinig DA and Turner JD 2006, Forest trees of Australia, 5th edition, CSIRO Publishing, Collingwood Australia.

Bootle K 2005, Wood in Australia: types, properties and uses, 2nd edn, McGraw-Hill, Sydney.

Department of Employment, Economic Development and Innovation (DEEDI) 2010, Construction timbers in Queensland : properties and specifications for satisfactory performance of construction timbers in Queensland, Class 1 and Class 10 buildings. Books 1 and 2. Department of Employment, Economic Development and Innovation, Brisbane.