Free Samples | Contact Us
composite decking

Common Types of Wood Deck Defects and Their Causes

Monday, April 15, 2024

Not much wood is perfect. In fact, most wood has defects. When making a deck, it’s important to understand the various defects in wood and how they can affect how the deck looks and how it will be used.

Lumber can have defects either during the growing process or after it has been cut and treated. All lumber is graded according to its quality. Purchasing highly rated materials from the start is the best way to avoid problems with your lumber.

Allowing the wood to dry completely before installation is also helpful, especially when using pressure-treated wood. Protective stains not only hide defects in deck boards, but also stop or slow the development of defects such as cracks by prolonging the drying process.

Various Defects in Traditional Wood Decking


Any change in the wood boards from one plane to another is known as warping. It occurs when the boards twist due to residual growth stresses or when the wood shrinks in different ways along its length, width, or radial planes.

Splitting and Dry Cracking

Splits are cracks in the surface of a board, usually in a straight line. It is usually caused by the wood drying out too quickly. Splits can accelerate damage to the boards by allowing water to enter the interior of the deck from the pressure-treated deck surface.

On the other hand, splits can run all the way through the boards, and severe splits can render the boards useless. Sometimes a split plank can be saved by cutting it.



Most woodpeckers live on cypress trees. The disease, which appears as a small black hole or pit in the wood, is caused by a parasitic fungus. After felling, the tree will no longer die. Many woodworkers look for “woodpecker” or “woodpecker” cypress because of its interesting wrinkled surface.


The process of decomposition of wood fibers is called rot and is usually caused by tiny organisms such as molds and fungi that eat wood. Fungi need air, temperatures between 40 and 100 degrees Fahrenheit, at least 30% moisture, and a food source like wood to grow.

Woods like cedar and redwood have natural “extractives” that prevent them from mold and rotting. Pressure-treated wood has chemicals added to it that are harmful to fungi and mold. To prevent rot, many paints contain mold inhibitors. Don’t allow your deck boards to get wet before or after you lay your deck. This will help prolong their life.

Wood Pith

The pith is the soft part in the middle of the tree, and if it is present in the boards, it is a defect. The pith is about 1/4 inch wide and as thick as a pencil. Be careful with the first three or four growth rings around the pith as well. These sections will open up and curl at the edges as they dry.


Annual Rotation Shake

Cracks that appear between and along the growth rings of a tree are known as annual ring jerks. This can be detrimental to the strength of the wood. Black spots and an odor similar to vinegar or rotting food may also appear. This defect is caused by parasitic bacteria and occurs mostly in wood with high moisture content.

Mineral Streaks

Mineral streaks are the name given to faded spots on some boards. They occur when dark minerals enter the tree from a water source or when mold grows. Some streaks are blue or brown in color and can be masked or removed with a dark stain. Cleaners containing oxalic acid can remove mold streaks.


There are many bugs that live in and eat wood. Diamondbacks, beetles, moths, wasps, and other insects are common. Moths are usually “secondary invaders” that are attracted to wood that is already weak, damaged, or dead.

Wood-eating insects leave behind feces that look like sawdust. The holes they make are usually circular and distributed in different locations in the wood. Insects are usually attracted to wood with more than 30% moisture content.


Resin, Gum, and Sap

Trees naturally contain these sticky substances which collect in cracks in boards, usually where the tree has been injured. The wood can become soiled with resin and sap, making it difficult to apply finishes.

Missing corners

Missing corners are the absence of wood at the corners of a board. This defect is usually only found on low-quality wood. Sometimes you can hide this defect by simply turning the board over.

Bending or Crowning

Wood boards that are bent from end to end are known as “bending” or “crowning”. This can occur if the wood has dried unevenly or if there are tree pits around the edges of the boards. You can cut the boards and replace them with straighter, thinner boards. If you are cutting the outside of pressure-treated deck planks, be sure to treat the edges or ends with an approved chemical treatment first.


Some boards will bend along the grain line, but not across it. This is known as curvature. If the board is laid on a flat surface, both ends of the board will be in the air. This defect can occur if the wood dries with uneven airflow. Bowed planks are difficult to cut due to the high forces inside the plank, and breaking the plank can be dangerous. When you want to make a crosscut to it, the bow should be facing up.



When a board bends in a “U” shape from edge to edge, this is “cupping”. One often finds this on boards cut close to the pith. Planed boards can be made from boards cut into pieces. If you try to force a curved board into the plane, it will probably split.


A board is said to be “twisted” if it bends in more than one direction and does not stay in a straight line. One corner does not always line up with the other corners. This usually occurs when the wood grain is not straight along the edges.

Wood knots

Wood knots are wood defects caused by tree branches. For the purpose of grading wood, we group knots into groups based on their size, shape and strength, or how well they are held in place. Most knots are ugly; they weaken the board or are used as a starting point for inspection. The higher the quality of the wood, the fewer knots there are.

  • Dead or loose knots. As a tree grows, its lower branches die and are replaced by new growth. These knots are caused by dead branches that are not attached to the wood. They are the easiest to dislodge.
  • Tight knots or closed knots. A tight knot has a flat surface without any holes. It does not weaken the wood. This type of knot is created by living branches.
  • Spiked knot. A spiked knot is an elongated knot that forms when the wood is cut almost as long as the knot (branch).
  • Needle knot. This is a small knot that is less than half an inch in diameter. For the most part, these small knots are secure and hard to see. Sometimes you can find them in higher quality wood.

Different Kinds of Manufacturing Defects in Deck Boards

Wood and deck boards develop these defects because the lumber is stressed during sawing and trimming.

Roller Check

When a depressed board is manually flattened between the rollers’ planes, this is a Roller Check. light roller checks are up to 2 feet long, medium roller checks are 2 to 4 feet long, and heavy roller checks are 4 feet or more.


Skip” is the rough surface left wherever the planer has planned. This occurs when the board is too thin for the planer knife to reach and smooth the entire surface.

Machine Burn

Machine Burn is the darkening of wood due to excessive temperatures, usually due to dull knives or blades. In most cases, this defect can be eliminated by sanding.


Selecting the Right Decking Material

The first thing you need to do to avoid using defective wood is to choose high-quality wood. The next thing you need to do is figure out what problems you’ve found and how they will affect the look and function of the deck. After a period of time, you’ll soon learn which defects matter and which don’t.

If you don’t want to spend too much time inspecting the wood, you can opt for composite decking material. Composite decking board is a great alternative to traditional wood, and it doesn’t have those common wood defects.

Composite decking boards are made from high-quality materials and strictly controlled processes. Therefore there are no natural or machine-made defects like wood. They can also be cut and joined like wood. Maintaining composite decking boards takes much less time and money than wood decks. While regular wood decking lasts between 10-15 years, composite decking lasts between 25-30 years.

Related Post

Popular Posts
How to Install a Floating Deck How to Install a Floating Deck
Wednesday, May 29, 2024
Floating decks are one of the types of decks that are built on the ground and it is not attached to any housing structure.
16 Creative Ideas for Patio Privacy Fences 16 Creative Ideas for Patio Privacy Fences
Monday, May 27, 2024
With a privacy fence, you can have fun with your friends on your patio without worrying about what your neighbors, or other people passing by, might see.
How to Frame Your Deck? How to Frame Your Deck?
Wednesday, May 22, 2024
A very important part of installing an outdoor deck is building the frame. It sets the stage for building a strong and long-lasting place to live outside.
Discover the 7 Best Woods for Fences Discover the 7 Best Woods for Fences
Monday, May 20, 2024
A proper fence will not only protect your privacy but will also better decorate your home. Choosing the right material is the first thing you need to do when starting a new fencing project.