Wood defects showcased on Forest 2 Home lumber Cherry wood boards. Defects include cracks, pitch, knots and shakes

Top 10 Artificial and Natural Wood Defects

For new woodworkers and seasoned woodworkers alike, it can be hard to identify wood defects. Lumber defects add unique features to a piece of wood and can be integrated into a woodworking project. While some wood defects compromise the structural integrity of the wood board, others impact the boards appearance exclusively.

Natural and artificial wood defects

Lumber defects can be broken down into two categories: natural and artificial defects. Natural defects occur during tree growth, with development of said defects not being able to be controlled by man. Natural defects include knots, shakes, Spalting, etc. Artificial defects are defects that are developed after the lumber has been harvested. These defects arise in various harvesting practices including drying and storage of the lumber.

Artificial wood defects


Bow, or bowing, refers to bending of the board along the grain lines. Instead of laying flat, a board that is bowing will have both ends in the air, though flatness across the face will not be impacted. Bowing comes about in the drying process of wood and can be avoided through proper drying time and practices.


A cup, or cupping, is similar to a bow but differs in that it warps along the sides of the board (edge to edge, turning the board into a “U” shape) instead of lifting at the ends of the board like with bowing. Cupped boards can be ripped into smaller boards and planed though forcing the full board to become flat will cause cracks.

Cracks or checks

Cracks and checks are another wood defect that occur in the drying process. As wood shrinks when it dries, the checks and cracks arise. As visible breakage along the length of a timber piece, they are often a cause for concern though in reality, checks and cracks are a natural “side effect” of wood drying, are likely to close or shrink overtime and will not compromise structural integrity.


Twist, or twisting, is more of a general term for a board that bends in various directions. Twisting may occur because of the grain pattern but it can also occur from improper drying techniques.

Ben, the Forest 2 Home general manager, shows the team a twisted board

Forest 2 Home hardwoods general manager showing F2H Shop team a board with a wood twist from kiln-drying


Wane is when bark is left along the edge of a piece of lumber. It is caused when surfacing machines or planers fail to remove all the bark from a low spot on the lumber though sometimes may be left behind intentionally to showcase the natural elements of the wood bark.

Wane featured on a Forest 2 Home Hard Maple board

Wane featured on a Forest 2 Home lumber 4/4 Hard Maple board

Natural wood defects

Natural wood character on Forest 2 Home wood board including knots, pitch, cracks and wane


Knots are dark, circular holes that can be found on woods surface. Knots are created from branches that cause living wood grain to grow around them. While knots provide beautiful curves and unique features along the wood grain, they can impact the structural strength of a woodworking piece. There are various types of knots including, but not limited to:

  • Face knot: face knots can be seen on the face of a board.
  • Edge knot: edge knots are seen only in sawn timber on the edge of a cut board.
  • Live knot: live knots are the root of the branch that becomes enclosed in the growing tree trunk. Live knots are structurally sound, with fibers from the branch and main tree being completely integrated.
  • Dead knot: the structure of a dead knot is only 25% sound, if not entirely lost.

There are important considerations to make when working with boards that feature knots. Woodworkers must be aware that knots minimize overall workability as they are harder and offer greater resistance. Knots also have varying structural integrity that must be accounted for when working with them.


Shakes, visible cracks, and fissures within wood, can come about due to shrinkage on aging trees, movement caused by wind and freezing of sap in wood cells, as well as other potential causes. Shakes appear in various areas of the tree, from heartwood to sapwood and arise in various forms including:

  • Heart shakes: heart shakes are cracks occurring in the heartwood, or the inner region of a tree. Heart shakes are indicative of tree decay and thin as they extend outward towards the sapwood.
  • Star shakes: otherwise known as radial shakes, star shakes begin in the sapwood and extend to inner regions. The main cause of radial shake development is severe temperature differences throughout seasons.
  • Cup shakes: otherwise known as ring shakes, these shakes are cracks that run parallel to annual growth tings. They development of these shakes is due to unequal growth of the timber.


Pitch defects occur in trees that product resin (softwood trees), due to excessive accumulation of the resin. There are various pitch defects including pitch streaks, which are lines formed from resin that run along the wood grain and pitch pockets, which are circular openings filled with resin.


Wormholes are created as larva burrow into a piece of wood. There is generally more concentration in some areas of a tree than others, making this defect not evenly distributed throughout. Worm holes are a sought-after wood defect, with DIY faux worm hole tutorials available online; they contribute dynamic texture and varying color to wood boards making them a unique feature!

Forest 2 Home Hard Maple hardwood showcasing Spalting and Wormholes

Forest 2 Home 4/4 Hard Maple hardwood showcasing Spalting and worm holes


Spalting is a fungal discoloration of wood, created in the initial stages of decay and then subsequently dried to prevent further decay. Spalting creates unusual coloration of black, pink, gray and multicolored streaks and mostly impacts hardwoods, like Hard Maple.


Want to learn about more wood defects? Looking for a specific kind type of natural character for your next woodworking project? Email marketing@forest2home.com for some additional information! Be sure to tag us in all of your Forest 2 Home projects by using hashtag #BuiltWithF2H wherever you share project photos on social media and by tagging us on Instagram using the @shopf2h tag. We can't wait to see what you create next! Happy Woodworking! 


  • Totally Bobby

    thanks this helped with a school powerpoint. good article.

  • bud meech

    Interesting article. Is there a way to remedy cupping or bowing to salvage your piece of lumber (hardwood)?

  • Cynthia Schaefer

    Love all the info!
    Though some pictures need better identifying.
    And I would be remiss if I didn’t double check all the info. So if you don’t mind I’m going to double check it.

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