Pitch Pocket
A pitch pocket is a well-defined lens-shaped opening between growth rings in softwood lumber that contains liquid or dried resin (pitch). They are most common in species like Douglas fir, pine, and spruce. Pitch pockets are graded as defects and can cause finishing problems if the resin bleeds through coatings.
In-Depth Explanation
Pitch pockets form when resin accumulates in voids between growth rings, typically in response to injury or stress experienced by the living tree. When the lumber is sawn and dried, the pocket may contain liquid pitch that can ooze out, especially when exposed to heat or sunlight. This resin bleed-through is a persistent problem in finishing because it can dissolve through paint and stain, leaving sticky, discolored spots. To deal with pitch pockets before finishing, woodworkers typically scrape out the soft resin, apply a shellac-based sealer as a barrier coat, and then proceed with topcoats. In grading, pitch pockets are measured by their length and width, and their impact on the grade depends on their size and quantity. Structural grading rules are generally more tolerant of pitch pockets than appearance grades.
Usage Example
The painter sealed every pitch pocket in the pine trim with two coats of shellac before priming to prevent resin from bleeding through the white paint.