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Common Wood Defects

Wood is far from a stable, consistent material. One of the biggest challenges of woodworking is learning to work within the constraints of a wood's properties. But before you can expect to work within these constraints you must understand them. It is for this reason we present you with the following article, Common Wood Defects.



Caused By



Blue Stain


A bluish gray discoloration on the woods surface. This feature is most common in woods like Holly, Pine, and Sycamore. Mold that grows in warm and moist area, usually poorly ventilated. Discoloration of wood. Can be cut off, placed out of sight, or concealed with a dark stain.
Bow A curve along the face of a board that usually runs from end to end. Improper storage. Usually moisture evaporation from one side and not the other. Stock is difficult to work with and cut. Cut in to smaller pieced, even out on a jointer, or nail (screws are better) in place with bow bulging out.
Checks or Splits


Breaks at the end of a board that run along the grain. Checks and splits are usually restricted to the end of a board. Rapid Drying. Can effect the strength and appearance of the board. Should be cut off or worked around.
Crook Warping along the edge from one end to the other. This is most common in wood that was cut from the center of the tree near the pith. Can be caused by improper drying and storage or the presence of reaction wood. Can be difficult to work with. The higher spots can be cut away on a table saw or jointer using a special jig.


Warping along the face of a board from edge to edge. This defect is most common of plain-sawn lumber. This defect can be caused when one board face dries at a faster rate than the other. Stock can be difficult to work with. Trying to "force it flat" can cause cracking along the grain. You can try allowing the board to dry at the same moisture content under pressure, rip it into smaller pieces on a table saw, or use a jointer to remove the high spots.
Dead or Loose Knot


A dark, usually loose knot. This is caused by a dead branch that was not fully integrated into the tree before it was cut down. Can mar the appearance of the wood, fall out, become loose, or weaken stock. Should be cut out, around, or glued in place and filled with a wood putty.
Gum, Sap, or Pitch


Accumulations of a resinous liquid on the surface or in pockets below the surface of wood. Injury to the tree. May cause difficulty when finishing. Should either be cut off or scraped out and filled.
Machine Burn Dark streaks along the face of a board. Usually caused by planer blades that are dull or spun on a part of the board for too long. Discoloration to the surface. Sometimes the burn can penetrate into the board. Can be sanded off or cut down with a jointer. The depth of the board often determines the amount of work needed.
Ring Check Breaks in the wood along the annual growth rings. Improper drying or damage during transport. Can effect strength or appearance. Should be cut around, place out of sight, or glued down.
Tight Knot


A know which is tightly integrated into the surrounding wood. This was once a branch that was incorporated into the tree as its girth increased. Does not effect the lumber's strength. May be removed for appearance purposes. Some lumber such as Knotty Pine, is highly prized for this feature.
Twist Warping in lumber where the ends twist in opposite directions. (Like twisting a towel) Growing conditions, uneven drying or the presence of reaction wood. Can be difficult to work with. Can be cut into shorter boards or the high spots can be removed on a jointer.


Small holes in the wood. This is caused by insects boring through the wood. Can be used to simulate old or wormy wood. Cut around worm holes or uses as is for decorative purposes. Be sure the insects are dead.

Revised: November 24, 2008.



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