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Thermally Modified Ash (Fraxinus excelsior) Hardwood
Thermally Modified Ash undergoes a controlled heating process (400°F+) that fundamentally transforms the wood's cellular structure — dramatically improving dimensional stability, decay resistance, and...
Janka Hardness
1,320 lbf
Durability Class
Class 1-2
Lifespan
25-30+ years
Stability
Excellent
What Is Thermally Modified Ash Wood?
Thermally Modified Ash undergoes a controlled heating process (400°F+) that fundamentally transforms the wood's cellular structure — dramatically improving dimensional stability, decay resistance, and durability without using any chemicals. The result is a beautiful, high-performance hardwood suitable for exterior applications that standard ash could never handle.
The thermal modification process caramelizes the wood's natural sugars, producing a rich, consistent brown color throughout the entire board — not just a surface treatment. This process also eliminates the food source that fungi and insects rely on, giving thermally modified ash decay resistance comparable to tropical hardwoods like Ipe and Cumaru.
With a Janka hardness of 1,320 lbf (slightly reduced from raw ash's 1,320 due to the modification process), thermally modified ash offers good surface hardness combined with dramatically improved moisture stability. Boards absorb up to 50% less moisture than untreated ash, resulting in significantly less swelling, shrinking, warping, and cupping — making it an excellent eco-friendly alternative to imported tropical hardwoods.
Key Facts
- Chemical-free modification process — only heat and steam are used
- Up to 50% reduction in moisture absorption vs untreated ash
- Decay resistance comparable to Class 1-2 tropical hardwoods
- Through-body color — brown tones extend through the entire board
- Eco-friendly domestic alternative to imported tropical species
- Available in standard decking, siding, and custom mill profiles
Why Choose Thermally Modified Ash?
Chemical-Free Durability
Enhanced decay resistance achieved through heat treatment alone — no toxic chemicals, preservatives, or treatments
Exceptional Stability
Up to 50% less moisture movement than untreated wood — dramatically reduced warping, cupping, and checking
Eco-Friendly Choice
Domestically sourced hardwood with a sustainable heat modification process — lower carbon footprint than imported tropicals
Consistent Color
Rich brown tones go all the way through the board — not a surface stain that wears away
Lightweight
Lighter than tropical hardwoods like Ipe, making handling and installation easier and faster
Good Thermal Properties
Stays cooler underfoot than darker, denser tropical hardwoods in direct sunlight
Common Applications
Thermally Modified Ash is well-suited for a range of interior and exterior applications.
Exterior Cladding & Siding
Facades, rainscreen systems, and exterior wall paneling where stability is critical
Decking
Residential decking and outdoor flooring — a domestic alternative to tropical hardwoods
Outdoor Furniture
Benches, planters, and garden furniture that needs to withstand the elements
Fencing & Screening
Privacy fences and screening with improved weather resistance
Pergolas & Structures
Garden structures, arbors, and architectural features
Sauna & Spa
Ideal for sauna interiors due to low thermal conductivity and moisture resistance
Thermally Modified Ash by Application
Learn how Thermally Modified Ash performs across different project types.
Thermally Modified Ash Decking
Thermally modified ash decking offers a sustainable, chemical-free alternative to tropical hardwoods for residential outdoor living spaces. The thermal modification process enhances dimensional stability by up to 50%, meaning ash deck boards resist warping, cupping, and checking far better than untreated softwoods. At 1,320 lbf Janka, the surface is hard enough for moderate foot traffic while remaining comfortable underfoot and noticeably cooler than darker, denser species in direct sunlight. The rich, through-body brown color provides a warm, contemporary aesthetic that complements modern architecture. Thermally modified ash decking works with both face-screw and hidden fastener systems, and its lighter weight makes installation significantly easier than ultra-dense tropical alternatives. For eco-conscious homeowners who want genuine hardwood performance without the environmental concerns of imported tropical species, thermally modified ash delivers a compelling 25-30+ year decking solution.
Explore all decking optionsThermally Modified Ash Siding
Thermally modified ash siding is rapidly becoming the preferred choice for architects and builders seeking sustainable exterior cladding with premium aesthetics. The thermal modification process makes ash dimensionally stable enough for rainscreen, shiplap, and tongue-and-groove siding profiles — joints stay tight through seasonal temperature and humidity swings. The consistent brown color extends throughout the board, so any surface wear or scratches maintain the same appearance. Ash siding's enhanced decay resistance (Class 1-2 rating) means no chemical preservatives are needed, and its domestic sourcing reduces the carbon footprint compared to imported hardwood cladding. The wood weathers to an attractive silver-gray if left untreated, or can be maintained with annual UV-protective oil for a warm brown facade.
Explore all siding optionsThermally Modified Ash Fencing
Thermally modified ash fencing provides a durable, eco-friendly privacy solution that outperforms standard treated lumber. The thermal process eliminates the food sources that fungi and insects depend on, giving ash fence boards genuine rot resistance without the chemicals found in pressure-treated alternatives. At 1,320 lbf, the surface resists dents and impacts better than cedar or pine fencing. The uniform brown color creates a cohesive, modern appearance, and the wood accepts stain if a custom color is desired. Thermally modified ash fence boards are lighter than tropical hardwoods, making installation faster and easier, while delivering 25-30+ years of service — significantly outperforming untreated softwood fences that may need replacement in 10-15 years.
Explore all fencing optionsInstallation & Working Tips
- Pre-drill for screws — thermally modified wood can be more brittle than raw ash
- Use stainless steel fasteners to prevent corrosion staining
- Handle with care — thermal modification slightly reduces impact resistance
- Allow 7-14 days for acclimation to local conditions before installation
- Standard woodworking tools work well — no carbide tooling required
- Apply end sealer to cut ends to prevent moisture entry at end grain
For complete guidance, see our installation guide and custom milling services.
Maintenance & Care
Thermally modified ash requires minimal maintenance. Its enhanced decay resistance means no chemical treatments are needed for outdoor use.
Color Preservation
Apply a UV-protective oil finish 1-2 times per year to maintain the rich brown color. Without UV protection, the wood will weather to a silver-gray patina while retaining its structural integrity.
Cleaning
Clean with mild soap and water or a hardwood deck cleaner. Avoid harsh chemicals. Light pressure washing is acceptable for deeper cleaning.
Inspection
Check fasteners annually and re-tighten as needed. Inspect end grain areas for any moisture entry and reseal if necessary.
Important Considerations
Reduced Impact Resistance
The thermal modification process slightly reduces the wood's shock resistance. Avoid dropping heavy objects and use furniture pads.
Brittleness Near Edges
Pre-drill all fastener holes near board edges to prevent splitting. The wood is less forgiving than raw ash.
Shorter Lifespan Than Tropicals
While much improved over raw ash, thermally modified ash typically lasts 25-30+ years outdoors vs 50-75+ for Ipe or Cumaru.
Frequently Asked Questions About Thermally Modified Ash
Quick answers to common questions
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