Check (Wood Defect)
A check is a crack or split in wood that occurs along the grain, typically caused by stresses during drying. Checks usually appear on the end grain or surface of lumber and do not extend through the full thickness of the board. They are distinguished from shakes, which occur between growth rings.
In-Depth Explanation
Checking is one of the most common drying defects in both hardwood and softwood lumber. As wood dries, the outer fibers lose moisture and want to shrink before the wetter interior, creating tension that can split the surface. End checks are especially prevalent because moisture escapes from end grain 10 to 15 times faster than from face grain. Applying end sealer or wax to freshly sawn boards dramatically reduces end checking. Surface checks on timbers and large-dimension lumber are often cosmetic and structurally insignificant, though they can admit moisture and accelerate decay if left exposed to weather. Grading rules allow varying amounts of checking depending on the grade and intended use of the lumber.
Usage Example
After air drying without end sealer, the cherry boards developed deep end checks that required trimming 6 inches off each end before they could be used.