Glossary - D

The decomposition of wood by fungi.

Timber used in surfacing parts of bridges and other structures subjected to vehicular or pedestrian traffic.

In timber and other forest products, the result of any process that lowers the value of the wood.

A kiln working on the heat pump principle. Moisture evaporated from the timber by a flow of warm air is condensed on the evaporator coils of a refrigeration unit and drained away. The refrigerant is compressed and passed through condenser coils, re-heating the air stream.

The separation of plies or laminations through failure of the bond, visible at an edge.

As applied to timber, density is the mass of wood substance and moisture enclosed within a piece expressed in kilograms per cubic meter. As the mass will vary dependant on the amount of moisture in the piece, density is often expressed at a specified moisture content, usually 12%.

The difference between dry and wet bulb temperatures. It is a measure of humidity.

The temperature at which the relative humidity of a body of air is 100 per cent. Further cooling causes vapour in the air to condense as water droplets.

Timber in which the annual rings are at an angle with the axis of a piece as a result of sawing at an angle with the bark of the log. A form of cross grain.

The change of a square or rectangular section timber to a diamond shape during drying. Diamonding occurs where the growth rings pass through diagonal corners of the section of the piece and is caused by the difference between tangential and radial shrinkage. It is a form of distortion.

1. In a beam, an element at right angles to the span with the function of connecting the beams so that they resist load as a unit. 2. A relatively thin, usually rectangular, element of a structure that is capable of withstanding shear in its plane and acts as a bracing elements.  

Movement of water through wood from points of high moisture content to points of low moisture content by molecular diffusion.

A measure of the rate of moisture movement through wood by diffusion as a result of differences in moisture content

Sawn - The nominal dimension of the board plus the overcut to allow for shrinkage. Nominal - The general intended size of the dry rough sawn board. Machined - The actual size of a machined or moulded board.  

Changes in the size of a piece of dry timber as its moisture content changes to be in equilibrium with the surrounding atmospheric conditions.  

Submerging timber in a dipping vat containing fungicides or other chemicals to prevent stain or decay.

Change in the colour of wood caused by fungal or chemical stains, weathering, or heat treatment.

A drying defect caused by the differential shrinkage along the three axes of a piece of wood. Distortion may take the form of cup, bow, twist, spring or diamonding.

A cylindrical timber rod or steel bar generally without nut or thread driven into pre-drilled holes to make a joint.

A joint where the pieces of timber are joined by dowels running either longitudinally or transversely through the joint.

Timber finished to a smooth surface on one or more surfaces.

A generic term for the decay of timber by fungi that at an advanced stage leaves the wood light and friable. The term is actually a misnomer as all fungi needs considerable moisture to grow.

A chamber or apparatus used for drying or conditioning timber or veneer in which the temperature, humidity and velocity of the circulating air are usually controlled.

The process of removing moisture from timber to improve its serviceability in use. Also see Seasoning.  

An imperfection developing during drying that decreases the value of a piece of timber.

A reduction in timber grade and volume as a result of drying defects

In kiln-drying wood, use of dry-bulb temperatures of 100 C (212 F) or more.

The reduction in volume and grade quality that can be attributed to the drying process. Pre-treatment - Special process taken before drying or early in the drying process to accelerate drying rate, modify colour, or prevent checks and other drying defects.  

The loss of moisture from timber or other wood products per unit of time. Drying rate is generally expressed in percentage of moisture content lost per hour or day  

The force per unit area that occurs in some zones of drying wood. It results from the uneven shrinkage that occurs with normal moisture gradients and from the set that develops in wood. A term loosely applied to any dry, crumbly rot but especially to rot that, when in an advanced stage, permits the wood to be crushed easily to a dry powder. The term is actually a misnomer for any decay, since all fungi require considerable moisture for growth.  

1. The natural resistance of timber to biodeterioration due to fungi, insects and mechanical breakdown caused by weathering, checking and splitting. 2. In building, the efficacy of details in preserving or protecting the fabric of the building from decay or deterioration.  

Durability is expressed as one of four classes. The value for each species is based on trials of the resistance to both decay and termites of untreated heartwood in the ground. The classes are: (1) Class 1- Timber of the highest natural durability, expected to have a life greater than 25 years in the ground and greater than 40 years exposed above ground. (2) Class 2 - Timber of high natural durability, expected to have a life of about 15 to 25 years in the ground and 15 to 40 years exposed above ground. (3) Class 3 - Timber of moderate natural durability, expected to have a life of about 5 to 15 years in the ground and 7 to 15 years exposed above ground. (4) Class 4 - Timber of low durability, expected to have a life of 0 to 5 years in the ground and 0 to 7 years exposed above ground. The sapwood of all species is regarded to be Class 4.