| A sampling of the most common defects found in stock timbers and panels. These are caused primarily by growth defects in the tree, improper curing of the rough cut timbers, or improper treatment/ weatherproofing of exposed wooden structures.
These defects are most common in whole, straight grain cuts. Plywood panels and other composites such as particle board are unlikely to have these flaws.
- Checking: The wood splits into a v-shaped channel near an end-grain cut, often following the curved lines of the growth rings.
- Cupping:The entire length of the plank curves along its grain. This is most often seen on decks or patios that were left untreated in the rain. Each plank has curved up along its length.
- Wane:Pieces of the timber chip or loosen near the edges of the cut, again following the curved growth rings. Here, two separate branches of the tree grew together over time trapping some layers of bark between them. When the timber is cut these pieces fall loose.
- Warp: Similar to cupping, except rather than curving along the grain lines (or the edge of the plank), the wood curves on a diagonal.
- Bow: The wood curves along the length of its face. It is easiest to picture by imagining a long plank layed on its face supported on either end but not in the center. If you jump on the center of the plank, you are causing it to bow.
- Bend:Similar to bowing, except instead of curving along the face (wide) part of the board, the piece curves along the length of an edge. This is rarer and almost never found in panels, only planks.
- Shake: A lengthwise separation of the wood through the growth rings. This will appear very similar to checking. Basically, a crack that follows the grain lines of a piece.
- Decay: Disintegration of the wood due to fungi. Also called dote, rot, or unsound wood. It can result in soft spots and discoloration in the piece.
These defects all severely weaken the strength and life expectancy of anything built from them. Often they are combined, sometimes resulting in amazing twists bends and curves in a single piece of what should have been a flat, straight plank. With the exception of checking and waning, which tend to be localized problems in the grain, all of these defects will grow worse over time. If you are building something to last it is important to carefully inspect the grain for hidden defects. Avoid yellow pine.
For a good carpenter these skills become nearly innate. Just hefting a piece or rapping on it can reveal internal defects that otherwise wouldn't show until it had been cut. | 
