Korina Thermally Modified Decking

Korina is the lumber trade’s name for Terminalia superba, a West African hardwood most people have seen without knowing it — Gibson built the Flying V and the Explorer out of it in the late 1950s and the name stuck. Elsewhere in the timber world the same tree is sold as Frake, Limba, Black Limba or Afara.

It has always been a pleasant wood to work: straight-grained, light for a hardwood, predictable under a blade. It has also, historically, been useless outdoors. Untreated Korina has almost no natural decay resistance, and a board left in the weather will not see out many seasons.

Thermal modification changes that completely. The lumber is cooked in a sealed kiln at roughly 400°F in an oxygen-starved atmosphere — no preservatives, no copper, nothing added but heat and steam. What comes out is a genuinely different material: rot-resistant, dimensionally stable, and a deep even brown all the way through the board rather than a color sitting on the surface. We stock it as 5/4x6 decking in two profiles.

Thermally modified wood is real wood transformed with heat and steam alone. The run takes 24 to 72 hours and comes in three phases.

• Drying. The wood is heated gradually while its moisture content is driven to near zero, preparing the cell structure for what follows.
• High-heat modification. Temperature climbs to 180–230°C (356–446°F) in an oxygen-deprived chamber. The hemicellulose breaks down, the cell structure permanently reorganizes, and the natural sugars and starches that attract insects and decay organisms are converted. The wood turns hydrophobic — it simply absorbs far less moisture than it used to.
• Cooling and conditioning. Steam is reintroduced as the wood cools, bringing moisture content back to a stable 6–8% and ready to mill.

The trade-off is strength. The process costs roughly a quarter of the wood’s breaking strength, which is why modified Korina belongs in decking, cladding, ceilings, trim and pergolas — and never in a structural span. Frame in something else and let the Korina be the surface you actually see. Anyone who does not volunteer that trade-off is selling you something.

• 5/4x6 S4S eased edge — the standard deck board, for face screwing and plugging.
• 5/4x6 grooved — milled on both edges for a hidden-clip system such as the ExoDek QuickClip, which sets the gap for you and leaves nothing on the surface.

Both are FAS grade, kiln-dried, and priced by the lineal foot. Other Korina profiles — cladding, ceiling, trim, pergola stock — can be milled to order through our custom millwork shop.

It machines, sands and finishes much like the unmodified wood, with one difference worth respecting: thermally modified timber is more brittle than raw stock.

• Pre-drill near board ends and at every fastener. Brittleness, not density, is the reason here — but the consequence is the same split.
• Keep carbide tooling sharp. Dull blades tear rather than cut modified wood.
• Collect the dust. The process produces a fine dark dust worth pulling off the saw.
• No further seasoning needed. It leaves the kiln at very low moisture content and largely stays there, so it moves very little on site.
• It takes finish well — oil and water-based stains and paints alike.
• Never use it structurally. Joists, beams, posts and stringers in something else; Korina is the walking surface.