What is Interlocked Grain?
Interlocked grain occurs when the wood fibers in a tree grow in one direction for several years, then reverse to grow in the opposite direction. This alternating spiral produces a grain pattern that is mechanically "locked" together, making the wood very difficult to split.
How It Forms
- The cambium periodically reverses the helical angle of new fiber cells.
- Adjacent growth layers have fibers oriented in opposite directions.
- The resulting interlock mechanically binds the layers together.
Visual Effects
- Ribbon stripe: Quarter-sawn boards show alternating light/dark stripes as fibers reflect light differently.
- Roey figure: A shimmering, wavy appearance caused by the changing fiber direction.
- Difficult planing: Grain reversal causes tear-out when planing in one direction.
Costa Rican Examples
Guapinol (Hymenaea courbaril)
Strongly interlocked grain makes this dense wood nearly impossible to split — ideal for heavy construction.
Espavel (Anacardium excelsum)
Moderate interlocked grain creates attractive ribbon figure in flat-sawn boards.
Practical Significance
- Split resistance: Ideal for tool handles, structural beams, and decking.
- Machining challenge: Requires sharp tools and reduced cutting angles.
- Drying difficulty: Interlocked grain increases warping tendency during kiln-drying.