Stair Parts

Thermory Benchmark Ash is the flagship hardwood product in Thermory's cladding and decking lineup — a thermally modified White Ash that sets the benchmark for what modified domestic hardwoods can achieve in exterior applications. Sourced responsibly from naturally renewing North American and Northern European forests, the ash is transformed through Thermory's proprietary "Intense" thermal modification process at 215°C (419°F) using only heat and steam. No chemicals, plastics, or additives are introduced at any stage — the transformation is purely physical, altering the wood's cell structure to permanently eliminate the food source for fungi and insects while dramatically reducing the board's ability to absorb moisture.

The result is a stunningly beautiful hardwood with an exotic, deep chocolate-brown color that runs consistently through the entire board — not a surface stain that can chip or wear away. Because the color is produced by molecular caramelization during modification, whenever the board is milled, cut, or sanded, the same rich brown tone remains visible. Thermory Benchmark Ash carries Durability Class 1 ratings under EN 350 — the highest possible durability class — with proven rot resistance for 25+ years in exterior applications, placing it in the same durability tier as tropical hardwoods like teak and ipe, but sourced sustainably from managed North American and European forests.

The performance advantages are substantial: equilibrium moisture content drops to just 4–7% (versus 18–22% for untreated ash), radial and tangential swelling are cut to under 3%, and Janka hardness measures approximately 4,450 N. Because the wood is naturally hydrophobic post-modification, it twists, cups, and bends significantly less than untreated hardwood — critical for the tight, gap-free seams demanded by modern architectural cladding profiles.

Each board is finished with Cutek Extreme Clear, a penetrating oil engineered to stabilize exterior wood from the inside out. Rather than forming a surface film like paint or varnish, Cutek carries its oils deep into the wood fibers, where they work continuously to slow moisture movement — the primary cause of cupping, checking, and end-splitting. Because the finish penetrates rather than coats, it cannot peel or flake, and maintenance requires no sanding or stripping — just clean the surface and reapply when it looks dry. The clear formulation adds no pigment, allowing the Benchmark Ash's rich chocolate-brown tone to show through initially before gradually silvering to a soft gray patina if left unmaintained with a colortone.

Ideal for premium architectural siding, cladding, soffits, porch ceilings, feature walls, decking, and porch flooring where the aesthetic warmth of exotic hardwood is desired alongside the sustainability and performance credentials of a domestically modified species.

Specifications