Lumber defects

A defect is an irregularity in or on wood that reduces the strength, durability and usefulness of lumber. Not all defects take away from the appearance of wood like knots. Knots can add to the appearence of certain projects.

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.

Question:

Listed below are common wood defects, using google or any search engine find images to match with each. Have you seen any of these defects in the past?

Wood Defect	Features	Caused By	Effect	Solution
Blue Stain Picture	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 Picture	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.
Cup Picture	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 Picture	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 PitchPicture	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 Picture	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.
Wormholes Picture	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.

Working with defects:

Bow Defect

Solution: Salvage a bowed board by crosscutting it into shorter sections, matching the lengths of pieces to the curve of the board. Test setups or finishes with areas too bowed to produce flat stock. You may be able to create small parts, such as cleats or spacers, from the bowed pieces.

Cup Defect

Cup: A board that rocks
from edge to edge
when laid on one face.

Cup Defect

Solution: Rip a wide, cupped board into narrow flat sections, as shown in Photo B, below right. Rip each piece slightly wider than you need, then re-rip or joint the edges square to the face. You even can glue these sections back together to create a wide board.

Rip cupped boards with
the convex face against
the saw table. A scrap
clamped to the fence
guides the workpiece
and holds the portion
being cut flatly against
the table.

Transform mildly cupped lumber into flat, thinner boards. First, joint the concave face flat, then plane the other face parallel.

Checks, Shakes, and Knots

Checks, shakes, and knots:
Checks are cracks across
the growth rings, and
shakes are cracks
between the rings. Knots
are remnants of branches.

Checks, Shakes, and Knots

Solution for checks and shakes: These cracks occur at the ends of boards, so you may simply cut off the bad areas. But don’t be too hasty. Good narrow pieces often exist on either side of a check.

Shakes, because of their orientation, usually have to be cut off. Be leery of boards with excessive shake. This may be a result of the board simply being dropped on one end, but shakes also can be a sign of improper drying.

Solution for knots: If they’re tightly held in the wood, knots usually pose just appearance problems. Use these boards in inconspicuous places where the knots won’t show. Loose knots, on the other hand, may fall out or be pulled free by cutting bits and blades. Cut out and discard areas with loose knots.

Crook Defect

Crook: A board that
rocks from end to
end when laid on
one edge.

Crook Defect

How you straighten the edge of a crooked board depends on the severity of the defect. If the crook is mild, run the concave edge over your jointer to straighten it. Use caution to prevent the leading end from catching on the outfeed table.

To put a straight edge on
a crooked board, stick
it on a long, straight
carrier, such as a strip
of plywood (about
3/4 x 8 x 60″), using
double-faced tape.
Guide the carrier along
the tablesaw fence to rip
off one bad edge.