Types of wood defects

Wood defects can be separated into two different categories:

• Natural
• Unnatural

Natural wood defects

Natural wood defects are those occurring during the growth of the tree, without any human intervention. They are often discovered during harvest. Some of the most common ones are:

• Knots
• Shakes
• Honeycombing
• Burls
• Galls
• Stains and discoloration
• Insect damage

Knots

Knots are round or oblong sections in the wood where a branch or twig once grew out of the wood. The area will likely be a darker color, and the grain will curve around it.

There are several different types of knots:

• Sound/closed/tight/live knots: Tight knots are intergrown with the grain and therefore won’t come loose.
• Unsound/loose/dead knots: These knots either already have fallen out or easily will in the near future. They are caused by a branch that didn’t get completely intergrown with the body of the tree before it died.
• Encased knots: These knots aren’t completely intergrown with the body of the tree. They may or may not be dead, but they aren’t loose.
• Knothole: The hole in the wood left when a loose knot fell out.
• Spike knot: These knots are oblong and can be shaped like a spike. They’re caused by limbs that were cut parallel to the length of the knot, revealing the end grain or the length part of the knot or limb. Generally, they’ll have splits and/or major grain deviation around them.
• Pin knot: These knots are small, less than a ½ inch in diameter. They’re typically sound and probably not as visible. Because they don’t usually interfere with work, you may see them in higher-grade lumber.

Shakes

Shakes are cracks that run lengthwise along a piece of wood between the growth rings. Usually, they travel the entire length of the face, and sometimes deeper inside.

Shakes can occur due to:

• Excessive frost action in the tree
• Wind stress
• The impact of a tree falling
• The shrinking of a log before the process of it into lumber

There are two types of shakes: (1) star or heart shakes and (2) ring, cup, or wind shakes.

Star or heart shakes are characterized by a group of splits angling out of the center of the tree in the shape of a star. They are wider on the outside and narrower on the inside. Extreme heat or frost during the growth of the tree are usually to blame for these.

Ring shakes form parallel to the growth rings. They’re often caused by:

• Bacteria
• Injury to the tree
• Aging of the tree
• Climate, such as excessive frost action in the sap when the tree is young

Ring shakes aren’t easily detected in green wood.

Honeycombing

Honeycombing is formed by internal stress in the tree, causing circular cracks to form inside the wood, like a honeycomb pattern.

This is one of the worst types of wood defects because you can’t tell it’s there just by looking at it, and it’s virtually irreversible once it happens.

Burls

Burls result when the tree receives a shock or injury at a young age. When this happens, the growth is greatly upset, leading to strange, irregular growths and projections like:

• Knots
• Twists
• Swirls

These irregularities form interesting patterns. The wood is often darker than in other parts of the tree—and may even be a completely different color. Sometimes, these unique patterns are highly prized among woodworkers for their novelty.

Galls

Galls are protrusions of wood substance from the trunk or limb of a tree. Sometimes, they’re referred to as tumors, as they look and behave like them. They are usually a response to an irritant, such as fungi, bacteria, or insects.

Sometimes, galls will disintegrate during the conversion process, but more often, they make the conversion process more difficult because of their coarse grain and the presence of knots, pith, or other irregularities.

Stains and discoloration

Discoloration has a couple different reasons. If it’s unnatural, it’s from machine burn. These are darker spots on the wood created because the machine knives or rolls were overheated.

If the stain or discoloration is natural, it is caused by fungal damage. Fungal damage can come in several different types and manifestations:

• Blue stain: With blue stain, fungi feed on the sap of the wood. It doesn’t harm the wood other than changing the color.
• Brown rot: This is the beginning stage of dry rot. Cracks will start to appear, having a darker color than the surrounding wood.
• Dry rot: When brown rot has advanced enough, the remaining cell walls of the wood disintegrate into a dry powder, which weakens the wood.
• Wet rot: With wet rot, fungi also break down the wood, transforming the timber into a gray-brown powder. If exposed to the elements, any wood that is unseasoned or improperly seasoned can easily develop wet rot.
• White rot: This is the opposite of brown rot. The fungi attack the lining and the wood itself, forming what looks like a white mass. Trees that develop white rot early on will have “spalted wood,” which some woodworkers will pay extra for. White rot doesn’t structurally compromise the wood.

Insect damage

Insect damage can cause a host of problems in a tree. Besides making unsightly holes and labyrinths of tunnels in the wood, it can eventually cause the wood’s strength to be compromised.

There are a few types of insects that cause damage to wood:

Wood-boring beetles: these voracious little bugs tunnel into the wood and deposit larvae, which consume the starchy parts of the wood. These include:

• Buprestid
• Powder post
• Ambrosia
• Furniture
• Longhorn

The well-known ash borer is one of these, as well as the beetle responsible for Dutch elm disease.

Pin-hole borers: These insects infect seasoned and drying lumber, as well as sick, dying, or live trees with bark injuries. The oak pinhole borer is an example of this type.

Termites: Termites eat the inside of a tree. Because of this, you can’t always tell there’s an infestation until the timber is being cut down and sawn. Termites will also attack already-seasoned lumber in a house or other construction.

Unnatural wood defects

Unlike natural defects, unnatural wood defects are caused by the conversion process—converting raw timber into wood for woodworking and other uses. These include:

• Compression failures
• Grain irregularities
• Wane
• Checks and splits
• Warping

Compression failures

Compression failures are a distortion of the wood caused by excessive end compression. They form wrinkles or cracks in the fibers of the wood and tiny deformations not visible to the naked eye.

A key indication of this defect is wide, distorted rings in the tree. If you see this, check closer to the center of the tree, where you may find compression failures. They can compromise the strength of the wood.

While compression failures can be caused by stress on a tree—such as falling on uneven ground—it’s most often caused by rough handling at any time during the conversion process or excessive stress during service.

Grain irregularities

Grain irregularities come about for a number of reasons. They may be caused naturally, as from a knot or burl.

But conversion may also cause grain irregularities like torn grain or diagonal grain. For example, diagonal grain can happen when the wood is sawn wrong. The growth rings sit at an angle, weakening the strength of the wood.

Wane

Wane occurs when the edge of a board is missing some wood or a strip along the edge is bark. This happens in the sawing process and is usually found in lower-grade lumber.

Checks and splits

Checks are cracks in the surface of the wood that usually run lengthwise along the board. A common cause of checks is drying the wood too quickly.

Splits are another separation, this time in the grain. Unlike a check, splits penetrate all the way through the board, reducing its strength and diminishing its appearance.

Warping

Warping is a general term for a wide variety of defects, such as:

• Twisting: The ends of a board turn away from each other, causing it to not lie flat anymore.
• Bowing: The ends of a board curve up lengthwise like the tracks of a rocking chair
• Cupping: The ends of a board curve up width-wise.
• Crooking: The board remains flat, but one end begins to curve in another direction.

Warping is often caused by improper drying methods as the wood undergoes shrinkage or by naturally occuring problems during the drying process, such as case hardening.

Having reviewed a number of common wood defects, you might wonder, are you able to use wood that has them?

Can I use wood with defects?

It really depends on the defect. Some defects are easily removed or worked around, while others affect the structure or strength of the wood.

Machine burn can be sanded away, along with some other stains.

Defects, like wane, can be resolved by sawing off the bad end. The board will be a bit shorter, but in some scenarios, this isn’t a problem. If checks affect just the end of a board, it can be sawn off. Splits could provide the location for sawing a board, making two smaller boards.

Other defects don’t need any altering to be used. Knots, for example, are present in a lot of softwood used for construction. In this situation, they usually won’t affect the building process or strength of the wood and can be safely used.

With some defects, judicious thinking is required. If you have some insect damage on one side of the board, but not bad enough to structurally harm it, you can face that side inward where nobody will see. Large (tight) knots could be on the underside of things like tables or chairs.

Some people also like to embrace defects and incorporate them into their projects for some really stunning results. Burls can make some beautiful patterns on a face, and blue stains could add some character to another project. Even knots and some shakes can be used to add scope to the project.

However, other defects are harder to work around or simply can’t be used.

Severe compression failures, for example, render the wood unsafe. Wood with honeycombing can’t be used either. Some grain irregularities weaken the board so that it shouldn’t be used. Dry and wet rot can destroy a board’s strength as well.

If you have a board with a defect, be sure to research it. If it doesn’t have defects that will harm the board’s strength, it may be salvageable.

Now, let’s look at some ways to prevent defects from happening.

How to prevent wood defects

While natural defects can’t be prevented, defects caused during conversion can be with the proper attention and care. Here are the steps you can take during each step of production.

Lumber production

From the moment a tree is cut down, defects can arise, and the first several weeks are the most critical. Trees cut between April and October will develop defects more quickly than trees cut during the other months because this is the time when insects and fungi are the most active.

Here are a few ways to help minimize defects during this time:

• Keep the logs wet or store them underwater. This helps minimize warping, checking, and cracking.¹
• Use an end coating. This can help prevent checks. Before applying an end coating, you can also spray on insecticide and/or fungicide to reduce the chances of insect infestation. Just be cautious with the sprays, as these can be harmful to people and animals.²
• Face the ends in the east/west direction, instead of north/south. The east/west direction will help reduce solar heat, which is very intense in the north and south directions.³
• Saw the logs into lumber within 15 days of cutting them, especially during the summer. Logs sitting on the ground and in direct sunlight can create a multitude of defects. If you can’t saw them then, it’s best to keep them off the ground, out of the sun, and preferably in water.⁴

Storage

After the green logs have been sawn into lumber, they have to be seasoned. This is another phase when defects can occur. Here are some best practices for prevention.

If you’re air drying the wood, avoid direct sunlight and stack the wood evenly, allowing plenty of air ventilation. This will help prevent all manner of warping, rot, and cracks.

Usually, if you’re not air drying, you’ll be using a kiln. If at all possible, keep the green wood in a climate-controlled place as it dries. It will dry quicker and help avoid defects from swinging temperatures and humidity. Stack the wood with spacers, which will help prevent twisting, bowing, and other general warping.

As they’re drying, be sure to check them with a moisture meter periodically. Doing so will help prevent you from using the wood before it’s totally dry and creating more warping.

Purchase of lumber

As someone purchasing lumber, you can avoid defective boards at the store or lumberyard with a few simple tricks.

Thoroughly inspect each board before buying it, looking for unwanted knots, warping, wane, insect damage, discoloration, checks, and shakes. Some of these, as we’ve said, can be resolved, hidden, or successfully incorporated into your project, but if that’s not you, that’s alright, too.

To check for warping, hold the long end up to your eye with the other end on the floor, and look down the length. Do this on all four sides.

You can also check the wood’s moisture content by bringing along a pinless moisture meter. Anything over 20% is still green and should not be purchased.

If you’re looking for minimal defects, know that the better quality of wood you buy, the fewer defects will be in it. Just be aware that this nicer wood will also be more expensive.

Building and installation

Before you use the wood you purchased, always give it time to acclimate. Wood continues to absorb and release moisture even after it’s seasoned. It will need time to acclimate to the moisture content of the atmosphere it will be in after the project is finished.

How do you know it’s acclimated?

A moisture meter!

Simply measure the wood on a regular basis. When the moisture content has stabilized, it has acclimated.

While it can’t prevent all defects, a moisture meter will help prevent a host of moisture-borne ones like warping or cracking. Preventing these problems will result in beautiful, solid projects worthy of your reputation and expertise.