The wood that is used for construction and other industrial applications is generally called timber or lumber. Timber also generally refers to trees from which commercial wood is obtained. If you have noticed, there are often some defects, gaps, knots, etc. on the surface of freshly sawn timber. One of the common types of defects in timber is ring shakes. In this article, We as a prominent supplier of high-quality hardwood and softwood timber will tell you all about the common types of defects that can be found in timber.
What are Timber Defects?
During or after milling, timber acquires a variety of growth characteristics. If they have unfavourable visual characteristics or have an impact on the timber’s structural integrity or properties, they may be regarded as defects in timber.
A tiny scratch on wood might not have an impact on its structural integrity, but it will make the piece useless for joinery. A flaw in a piece of wood could lessen its structural suitability but might improve its aesthetic appeal.
Defects in timber can be responsible for reducing the wood’s strength and durability, lowering its usability in commercial applications, lessened appearance, and decay.
Categories of Different Types of Defects in Timber
The different types of timber defects can be divided into the following five categories:
- Natural Timber Defects
- Seasoning Defects
- Fungi Defects
- Defects due to insects
1. Natural Timber Defects
Natural flaws in lumber are characteristics that arose while the tree was still alive or shortly after it was cut down and may reduce the timber’s usefulness. In many cases, it is more cost-effective to repair natural defects like dead knots. This category consists of all the defects that, from an engineering perspective, appear in a tree as it grows.
Knots, cross-grain, crookedness, shakes, rind galls, burr, and curl are the most common types of natural timber flaws.
The chemical reaction that any external agency causes with the wood can occasionally force it to change colour or hue. Chemical stains are the common term used for this type of defect. Frost can also cause changes in the appearance of wood, particularly in outdoor settings where the wood is exposed to extreme temperatures.
A branch’s growing location on the tree is indicated by a knot. It is most immediately identified on the cut board by its noticeably darker appearance and tougher nature. Essentially, a knot is an irregularity in the wood, which makes it a weak spot. Sometimes, knots can also contain resin, which can affect the wood’s appearance and durability.
The annual rings widen as the tree develops quickly. It is referred to as coarse grain wood, and such wood has less strength.
Bark and gall on the rind denote abnormal growth. The so-called Rind Gall is a distinctively curled bulge that can be discovered on the tree’s body. They grow when branches have been inappropriately chopped off or eliminated. They are hardly ever seen in trees, and the wood here is incredibly frail and not long-lasting.
Cracks and fissures are other names for shakes. These organic fissures could be caused by shrinkage as a result of the tree ageing, wind-induced movement in the developing tree, and sap freezing in the cells during growth. The timber’s resistance to shear is significantly reduced by the shakes, which is their most significant impact. As a result, if there are high shear stresses present, it is vital to refrain from using timber that contains shakes.
Dead wood, which is characterized by the absence of wood, can be found in timber harvested from standing dead trees. Its thinness and ruddy colour serve as indicators.
Also commonly known as wandering hearts, these defects are brought on by young trees being bent by a wind that is blowing quickly. The twisted strands in the wood make them unsuitable for sawing.
These signify wood fibres that have been damaged by compression or crushing, leading to internal stresses. The disturbances are primarily caused by inappropriate tree felling and exposing young trees to strong winds.
They are specially developed when a young tree is shocked or injured. The tree’s growth is severely disrupted as a result of the injury, and abnormal projections start to show throughout the body.
2. Seasoning Timber Defects
These defects in wood develop during the drying process. The rate and extent of drying must be carefully managed to avoid problems. Many recently cut timbers weigh more than half of their weight in sap or moisture. Simply put, seasoning is the process of drying out wood such that it is pre-conditioned (or shrunk) before use. The moisture content of the timber is lowered during this process to match the humidity in the air to ensure more stability.
Some common types of seasoning timber defects are as follows:
Typically, inadequate stacking during seasoning results in bowing in timber. It is a significant flaw in wood that limits the usage of good wood to short lengths.
A board’s springing is its edge-to-edge curvature. During seasoning, internal pressures are typically released, which is what causes it.
Twisting or winding
The highly dangerous condition of winding, also called twisting, limits the usage of the wood to very small lengths. It results from inadequate seasoning and stacking.
Flat-sawn boards frequently have cupping. The timber contracts as a result of drying shrinkage.
3. Fungi Defects in Wood
Fungus is also responsible for the decay of wood and might result in different types of timber defects as explained below:
A certain species of fungal causes the sap of wood to become bluish in colour.
Certain forms of Fungi strip cellulose molecules from wood, causing the wood to take on a brown hue.
Exactly the reverse of brown rot, in this, the lignin in the wood becomes a white mass made of cellulose components during this specific form of fungal attack.
Some types of fungi result in the chemical degradation of wood, which turns the wood into a powdery, greyish-brown substance. Wet rot is the term for it.
Some fungi feed on timber and break it down into a dry powder. It is called dry rot.
When atmospheric agents attack heartwood, the tree gets weakened. It will usually make a hollow sound when struck upon.
4. Timber Defects due to Conversion
Conversion is the process of turning raw timber into different forms such as planks, generally by using a saw or a power machine. Some species of wood might undergo physical changes due to or during the process of conversion, resulting in the following defects:
Chip mark on the surface of finished timber is a common defect that is caused due to the marks left by chips on timber.
This happens when the fall of timber results in a small depression or mark on the finished surface of the wood.
This type of defect is caused by careless sawing of timber, where the wood grain is at an angle and results in the formation of diagonal marks on the surface of the wood.
This type of defect involves a finished or trimmed piece of wood still having a part of the original rounded bark on its surface.
5. Types of Timber Defects due to Insects
These defects are caused due to the attack of insects like termites and beetles on raw wood or ready-to-use products. The common types of insects that can attach timber include:
Defects due to Termite Attacks
When it comes to insect attacks, termites are the most hazardous to structural timbers. In most timber species, termites can attack both the sapwood and the heartwood. but favour the pith and sapwood. The various termite flaws include Cypress pine, Grey Ironbark, Red Gum, Jarrah, Tallowwood, and Turpentine.
Wood Defects due to Beetle Attack
In wood, they create pinholes with a diameter of around 2mm. The beetle’s larvae create tunnels in sapwood, turning the wood into a powder that resembles flour. They don’t damage the cover or the exterior shell.
If you are concerned about different types of defects in timber or need expert guidance to identify and deal with defects in your timber, feel free to contact us at White Knight Consulting Ltd UK.