Defects in Wood

Common Defects and Characteristics Found in Wood

Wood is a natural material, exposed to differing and unpredictable conditions as it grows, wood often develops features which are undesirable to the woodworker.

The most important of there are listed below. Remember, however, that what is a defect to one worker may be a ‘feature’ to another. Fungal stains such as spalting, for example, may be considered attractive, provided they do not weaken the wood to much for its intended purpose. Adventurous and experienced wood-turners and furniture makers may enjoy using wood with splits, bark inclusions and other features which are normally avoided - beauty is in the eye of the beholder.

Wood is our most versatile material and as renewable resource it is continuing to be the first choice in so many industries.

See also Glossary of Wood Terms and Figure in Wood

Common Defects in Wood | Wood Defects

Bark inclusion or pocket

A piece of bark wholly or partially enclosed within the wood, which is weakened as bark a result.

Blackheart

Abnormal black or brown discoloration of the heartwood, which is not necessarily decayed. Ash (Fraxinus spp.) can be prone to this.

Blue stain, sap stain or sapwood stain

A bluish or light grey discoloration of sapwood, brought about by the growth of dark-coloured fungi in the interior and on the surface of the wood.

Bow

The form of warping in which a board is bent or bowed lengthwise.

Brittleheart

Heartwood that snaps easily across the grain as a result of compression failure in fibres during growth.

Canker

A disease-damaged area of a tree, usually caused by bacteria or fungus.

Case-hardening

A defect of seasoning, where the surface of the wood dries faster than the core. This cases permanent stresses and ‘set’ (deformation) that are released when the wood is cut, resulting in severe distortion.

Check

A longitudinal crack that does not go through the whole log or plank; usually caused by too-rapid seasoning.

Chipped grain

Torn grain due to poor machining or finishing.

Collapse

A caved-in cell structure, caused during drying, giving a shrivelled or irregular appearance.

Common furniture beetle

Anobium punctatum, commonly known as ‘woodworm’, one of the most widespread insect pests. The damage is done by the grub, which can live in the wood for up to two years before emerging as an adult.

Compression wood

See reaction wood

Crack

A large radial check, cause by tangential shrinkage being grater than radial shrinkage.

Crook

Similar to bow, but curving in the plane of the thin edge, rather than the wide side of a board. Also can be a tree typified by a sharp bend in the stem.

Cupping

Bending as a result of shrinkage across the width of a board.

Death-watch beetle

Xestobium rufovillosum, a beetle that is about 6mm long and very destructive to structural beams. The adults make a ticking noise.

End check

The separation of wood cells along the grain at the end of a piece of wood, cause by uneven drying.

Gum, sap and pitch

Resinous liquids found on the surface or in pockets in the interior of certain woods.

Gum canal

Resinous liquids found on the surface or in pockets in the interior of certain woods.

Hearth pith

The soft, spongy heart of a tree, which may appear on the surface of sawn timber.

Heart shake

A split that starts at the heart of a log.

Honeycombing

A network of checks in the interior of timber, not seen on the outside.

Knot

A section through a branch or twig which became embedded in the tree as the trunk continued to grow around it. Several types may be distinguished.

Branched knot

Two or more knots coming from a common centre.

Dead, encased or loose knot

Formed when the trunk grew round a dead branch. The knot is surrounded by a ring of bark and is often decayed. It may fall out, leaving a knot hole.

Live, inter-grown or tight knot

The base of a living branch, surrounded by growth rings and firmly fixed in the surrounding wood.

Pin knot

A knot whose diameter does not exceed 13mm. 

Spike or splay knot

A knot which has been sawn lengthwise when the wood was converted. It may be tight at the base, but loose near the surface of the log.

Lyctid borer

See powder-post beetle.

Machine burn

Burn marks on the surface of converted wood as a result of poor sawing or machining.

Pitch pocket

Burn marks on the surface on converted wood as a result of poor sawing or machining.

Powder-post beetle

A beetle (Lyctus spp.) which attack the sapwood of hardwoods with large pores, including ash (fraxinus spp.) and oak (Quercus spp.).

Reaction wood

Abnormal wood formed under the stress of compression or tension during growth, such as on the underside of a branch or learning trunk (compression wood), or the upper side of a branch near the trunk (tension wood). The cells are typically shorter and thicker-walled, with spiral markings. The wood tends to be a poorer quality and not desirable for commercial purposes.

Ring check, ring failure or ring shake

A separation of the wood fibres parallel to and between annual rings in the growing tree.

Rot

A generic term for several types of fungal decay, such as:

Brown rot

The cellulose and associated carbohydrates are attacked, but not the lignin. This usually gives a light brown stain and a friable texture. At an advanced stage the wood will split along rectangular planes as it shrinks; this is referred to as cubical rot.

Butt rot

A common disease in which fungal infection degrades the roots and steam of a living tree. Frequently caused by the fungus Heterobasidion annosum.

Dry rot

A general term applying to any crumble rot, but particularly one in which of the wood is easily crushed into powder; typically caused by Heterobasidion annosum.

Soft rot

This occurs in the outer layers of wood in very wet conditions, such as in boats. The secondary cell walls are attacked by microfungi that destroy the cellulose content. Typically caused by the fungus chaetomium globosum.

Wet rot

Usually occurs in persistently damp conditions, and can be caused by a wide variety of fungi.

White rot

A variety of fungus that attack lignin and cellulose, creating a spongy, stringy mass, which is usually whitish, but may have shade of light brown, yellow or tan.

Sap or sapwood stain

See blue stain.

Shake

A split in wood, normally parallel to the growth rings.

Skip

An area of a board that the planer has failed to surface.

Spalting

Partial fungal decay that often causes discoloration or fine irregular lines. It can be attractive for decorative turnery and the like, but the wood has lost its strength qualities.

Twist

A type of warping in which the ends twist in opposing directions.

Wane or waney edge

The presence of the outer surface of the trunk on the edge or corner of a board; bark may be present, or part of the edge may be missing.

Warping

Any deviation from a true or flat surface. This can include bowing, crooking, cupping, twisting or a combination of these.

Wormhole

Any hole made by boring insects of their larvae.

Source/reference: Wood ID & Use by T. Porter - A really great book for wood reference - CLICK HERE TO BUY

Posted by Paul Hayman on Monday 26 June 2017 at 10:46