Species
Description of rubberwood
While the rubber tree is planted to produce rubber, the tree ceases to produce latex at a viable rate at the age of 25-30 years. Generally, the trees are then felled, the land cleared and the area replanted.
Macrocarpa pine - properties and grading
Macrocarpa pine is the common Australian name for a species of tree, Cupressus macrocarpa, widely used in Tasmania in windbreaks. The species is a native of California, USA where it is known as Monterey Cypress.
Characteristics
Acoustic properties of timber
Timber construction can play a large part in both room acoustics and acoustic separation.
Corrosive action of wood on metals
Corrosion of metals by wood can sometimes occur when the wood is wet or is used unseasoned.
Electrical Conductivity of Timber
The electrical resistance of timber varies greatly with moisture content, from many thousands of megohms when very dry to near zero at the fibre saturation point (fsp, approximately 30%).
Fire Resistance Level
Fire Resistance Level (FRL) as defined in the Building Code of Australia (BCA) is the grading period in minutes for three criteria: structural adequacy, integrity and insulation.
Insulation properties of wood
Timber is a natural insulator. Air pockets within its cellular structure make timber a natural barrier to heat and cold.
Joint design and joint groups
For the purpose of joint design, all species have been classified into six joint groups; J1 to J6 for the unseasoned condition and JD1 to JD6 for the seasoned condition.
Softwoods and Hardwoods
The terms "softwood" and "hardwood" do not indicate softness or hardness in particular timbers.
The effects of temperature variation on timber
Strength of timber is affected by temperature. At below freezing temperatures, strength values for bending and compression, and for resistance to shock, are slightly higher than for values at normal temperatures.
Thermal Properties: expansion and insulation
Thermal expansion of wood is insignificant in most cases.
Timber Hardness
Hardness refers to the difficulty in sawing, planing, resistance to wear or abrasion and the resistance to indentation.
Wood structure - sapwood and heartwood
The light coloured wood adjacent to the bark is called sapwood, the darker remainder is heartwood. With time, the sapwood adjacent to the heartwood is converted into heartwood and the by-products are termed extractives. Extractives have a marked effect on the properties, particularly durability.
Colour variation in timber
Most timbers show variation in colour between species and within species. Colour descriptions usually relate to the heartwood. Finishes, light and weather all affect colour.
The definition of grain
The term grain refers to direction, size, arrangement, appearance, or quality of the fibres in wood.
Description of figure
Figure refers to the pattern produced on the surfaces of timber resulting from: the nature of the grain, the arrangement and realtive dimensions of the cells and colour variations. Major figures are: birds eye, fiddleback, ropey, ribbon, swirl, wavy and wild.
Description of wood texture
Timber can be coarse, fine, even or uneven. Texture is dependent on the size and arrangement of the wood cells.
Definition and description of timber density
As applied to timber, density is the mass of wood substance and moisture enclosed within a piece expressed in kg per cubic metre. Three main categories of density - green, dry and basic.
Preservatives
Commentary on AS1604 1997 (Preservative treated timber)
This article is a commentary for designers and contractors on "AS 1604: 1997 Timber - Preservative Treated - Sawn and Round" by Peter Campbell
Preservative Treatment - Light Organic Solvent Preservatives (LOSP's)
Light organic solvent preservatives (LOSPs) are regarded mainly as fungicides, with major toxicants of copper, zinc, tin or pentachlorophenol (PCP).
Preservative Treatments - Ammonium Copper Quaternary (ACQ)
ACQ is an arsenic and chromium free preservative treatment used for timber both in ground contact and above ground exposures.
Preservative Treatments - Boron Salts
Boron provides effective protection against attack by insect borers. It has been used in Australia for more than 40 years to protect the sapwood of susceptible hardwoods against lyctid or powder post borers.
Preservative Treatments - Copper Chrome Arsenate (CCA)
Copper Chrome Arsenate (CCA) is the most commonly used preservative in Australia. The treatment process involves impregnating the sapwood with preservative by a vacuum/pressure process in specially designed treatment plants.
Preservative Treatments - Creosote
The use of creosote in Australia is restricted to railway sleepers, piles and other heavy engineering applications due to the odour and surface condition of treated timber.
Quality Assurance of Preservative Treatment
When required, sampling and analysis of preservative treated timber can be specified.
Safety
Material Safety with Timber and Timber Products
Timber and timber products have to be handled and machined safely on building sites and in workshops. Saw dust needs to be collected at the point of generation and some timbers have known toxicological effects.
Timber grades and grading
Description of timber strength and stress grading.
The strength of structural timber is described in terms of "stress grades". This allows material with similar physical properties to be grouped together to meet the requirements of specific end uses.
Grading of Radiata Pine
Pine products are graded in various ways depending upon their end usage. There are two types of products: Appearance and Structural.
Moisture Content
Measuring moisture content
There are three common methods of measuring moisture content: the oven dry method, electrical resistance and capacitance type moisture meters.
Safe Working Practices with Timber
Wood dust may cause irritation and repeated inhalation may damage health and increase the risk of nasal cancer.
Definition and description of moisture content
Moisture content (MC) is the weight of water contained in a piece of timber, expressed as a percentage of the weight of oven-dry wood. Newly cut wood has a high MC. Moisture will continue ot be released from the cell walls until it stabilises at an equilibrium moisture content (EMC)dependent on relative humidity and ambient temperature.
Moisture movement
Movement describes the periodic small dimensional changes that occur in seasoned timber as it varies its moisture content due to environmental changes. This movement may be either shrinkage or swelling.
Moisture movement and shrinkage
As wood dries below its fibre saturation point it shrinks. Timber shrinks longitudinally, radially and tangentially.
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