Characteristics

Natural Characteristics & Manufacturing Imperfections 

Grades are determined by the natural characteristics of the log and any manufacturing imperfections that may occur during timber processing. Log characteristics will appear in a given piece of timber and affect its strength, stiffness and appearance. Manufacturing imperfections may also affect grade. 

Grades are determined by complex sets of criteria that consider the type, size, closeness, frequency and location of all characteristics and imperfections within a piece. 

Natural characteristics and imperfections are evaluated in several ways: 

• Timber graders visually judge the total effect of the various combinations of characteristics and imperfections, relative to the limitations set forth in the grading rules for each grade and species, and assign appropriate grades accordingly. Most timber production is graded by visual inspection.

• Sophisticated, state-of-the-art computerized grading equipment digitally scans the characteristics and imperfections in a timber piece, then electronically calculates and assigns the grade based on criteria set forth in the grading rules. 

• In the case of machine stress-rated (MSR) timber, each piece is non-destructively tested with stress-rating equipment to calculate the combined effect of the characteristics and imperfections on strength. MSR grades are provided numerically to facilitate engineering. 

Some of the more common characteristics and manufacturing imperfections are shown below to emphasize appearance details. 

 

Checked Knot	Tight Black Knot	Intergrown Knot	Not-firmly Fixed Knot
Spike Knot	Sloughed Knot	Unsound Knot	Wane
Bark Pocket	Pitch Streak	Brown Stain	Blue Stain
Machine Burn	Machine Gouge	Torn Grain (from Planer)	Skip in Dressing