11 most Common Lumber Defects and Their Remedies

Most of lumber defects adversely affect a board’s appearance, strength, and ability to take a finish. However, sometimes the defects or abnormalities can actually make a piece of wood more desirable, for instance, when they produce a unique attractive figure like Eagle’s eye or clouds, etc. The decisive factor is the use of wood, what may be an imperfection to one woodworker could prove to be another’s selling point. For example, knots are considered a significant defect in boards intended for a tabletop, but they are an essential feature of some types of paneling. Defects in lumber are also called imperfections, abnormalities, or faults. Generally, these defects are grouped into two broad categories; natural defects and seasoning defects (or man-made defects).

Natural Lumber Defects

Lumber defects are either natural or man-made. It might sound strange but every natural wood possesses defects that are caused by growing conditions or characteristics of the species itself. The same type of defect may be present in different types of wood. Some imperfections are found in all wood species. For instance, loose knots are caused simply by the way trees grow. They are the leftovers of broken branches that have become enclosed by the growth of new wood. Other natural defects include gum in most hardwoods, pitch in softwoods, and reaction wood in all species. Natural forces such as wind, fire, insects, and fungi can also cause defects in wood. A well-known defect of this type is a blue stain.

Seasoning Defects/Man-made Defects

Seasoning defects or man-made defects are those which are a result of poor seasoning or drying. Several defects occur when the wood is exposed to the air and allowed to dry. As wood does not shrink uniformly in all dimensions, warping can result when the moisture content of lumber drops below a certain level. Some common seasoning defects are checks, cups, bows, twists, crooks, and splits. It must be kept in mind that these defects can also occur in boards cut loose to the pith of a log.

What are common wood defects and their remedies?

Tight Knot

It appears as a whorl (or curl) that is inter-grown with surrounding wood tissue. Knots form as the girth of the tree increases, gradually enveloping the branches. If the branches are still alive at the time of their envelopment, the knot integrates with the wood in the tree trunk. A tight knot does not seriously weaken a board; it can be cut out or used according to the demand of the project.

Loose or Dead Knot

A loose knot appears as a curl encircled by a dark ring. When a branch dies, the remaining stump is eventually enveloped by the trunk. But the dead stump cannot integrate with the tissue surrounding it, thus creating a loose or dead knot. It is highly recommended to remove loose or dead knots before working with the lumber.

Gum

Most woodworkers are familiar with gum, it is an accumulation on the surface of the board or in pockets within the board. It usually develops when a tree has suffered an injury, is attacked by insects, or is exposed to fire. Wood with gum is not recommended to be used where a quality finish is required, as the gum will bleed through most finishes.

Checks

Checks are longitudinal splits or ruptures in the wood. They are usually caused by rapid drying. Checks may compromise the appearance and strength of the board. They could either be filled with epoxy or better cut off. Wild Edge Woodcraft provides one of the best wood drying services in North Carolina, as we have iDry Vacuum kilns and all the expertise to season your wood accurately.

DEFECTS

Image from wikipedia.org

BOW

It is an end-to-end curve along the face that is usually caused by improper storage of lumber. Bow produces internal stresses in the wood that make it difficult to cut. In order to deal with bows, flatten bowed boards on the jointer or first cut them into shorter pieces and then use the jointer.

Cup

The wood cup is an edge-to-edge curve across the face of the board. It is generally caused when one face of a board dries more quickly than the other. This defect is most common on peripherally cut stock, on boards cut close to the pith. It can also occur if one face of a board has less contact with the air than the other. A lumber cup may correct itself if both faces are allowed to dry to the same moisture content. Cupped boards can be recovered on the band saw or jointer.

Twist

Irregular or uneven warping where one corner is not aligned with the others. Twisting occurs from uneven drying or due to a cross-grain pattern that is not parallel to the edge. To overcome twisting, it is better to cut shorter boards or use a jointer.

Crook

It is an end-to-end curve along the edge of the lumber. Crook is caused by inappropriate seasoning or having the pith of a log close to the board edge. It reduces the strength of the wood, thus making it less suitable for weight-bearing applications. Crooked boards can be salvaged on joiner or table saw.

checks

Splits are similar to checks and appear as separations along the growth rings. They are also called as ring checks or ring shanks. Splitting results from improper drying of wood and damage due to felling. Boards with splits can be used, they could also be filled with filling materials but they become more noticeable when a stain is applied.

Machine Burn

Machine burn appears as a dark streak across the faces or edges of the lumber. It occurs when planer knives are dull or spin on one part of the board for too long. Machine burns can easily be removed with a jointer or sander.

Blue Stain

It appears as a discoloration of the surface on otherwise normal-looking wood. It develops from molds that flourish when lumber is dried or stored in warm, moist, or poorly ventilated conditions. Species like Pine and Sycamore are prone to blue stains. I find Blue Stain aesthetically pleasing and tend to accentuate it as a feature rather than a defect.

Although it is almost impossible to buy wood that is completely free of defects, you can obtain the best lumber for your projects by selecting the wood carefully. Wild Edge Woodcraft provides all the necessary information and expertise to produce the best quality lumber for your projects. We are here to properly mill, air dry, kiln dry, heat sterilize and flatten your slabs, reducing the chances of defects.