Thermory® Ash D45J 118 x 21mm

– Thermory® Ash D45J 118 x 21mm profile
– Thermo-treated decking boards
– Maximum stability and dark, rich colour
– Class 1 durability equal to Ipe and Teak
– Pre-grooved for use with ‘Clip-Strips’
– Half the weight of IPE – perfect for roof terraces
– Outstanding grain detail and durability
– Eco-friendly, sourced from responsibly managed forests in North-America
– Chemical-free process ensures low moisture content and improved decay resistance
– Transforming ash into a high-quality decking material with exceptional performance.

The Thermory® Ash D45J 118 x 21mm decking boards are crafted from high-quality ash wood sourced from North-American forests. Known for its durability and stability, this real-wood decking material boasts a luxurious color and is easy to install. With class 1 durability credentials comparable to Ipe and Teak, this timeless decking option is both long-lasting and barefoot friendly.

One of our greatest strengths is our well-organized delivery system. Whether we use external couriers or our own fleet of vehicles, we ensure your decking arrives promptly and in excellent condition. Delivery charges are calculated based on your postcode, the distance to your location, and the length and weight of the materials. For more details, please see our Delivery Terms & Conditions.

Overview: Choosing the Right Installation Method

Thermo-treated profiled timber decking combines exceptional dimensional stability with natural beauty, offering superior low-maintenance performance for outdoor living spaces. Available in ash and pine, thermal modification uses only heat and steam to enhance durability and weather resistance without chemicals. Choose from innovative hidden fastening systems or traditional face screwing to suit your project requirements.

Preparation and Acclimatisation

Before installation, allow the decking boards to acclimatise on-site for 48-72 hours. Store them flat, off the ground, and protected from direct sunlight and moisture. Although thermo-treated timber exhibits superior dimensional stability, proper acclimation ensures optimal performance. Seal all cut ends immediately with wax emulsion end grain sealant to prevent moisture infiltration.

Fixing Methods

PaCS® Hidden Fastening System (For PaCS® Profile Boards) The innovative PaCS® system delivers a flawless deck surface with remarkable installation simplicity. PaCS Strip is a six-clip strip fastening three boards sideways onto one joist. Boards fasten to clips with a simple click mechanism—no screwing required. The system automatically creates consistent 5mm gaps and provides 5mm elevation above joists, preventing wood-to-wood contact while ensuring proper ventilation.

TENI Clip System (For D34 Profile Boards) The TENI system offers versatile hidden fastening for D34 profiled boards. Manufactured from UV and weather-resistant polyoxymethylene, it creates consistent 6mm gaps between boards. The 8mm clip thickness provides essential ventilation space above joists. Includes stainless steel screws suitable for timber and aluminium joists.

Face Screwing Method For maximum board contact and traditional installation. Always pre-drill and countersink all screw holes—thermal modification can increase brittleness, making pre-drilling essential to prevent splitting. Use stainless steel screws exclusively (AISI 304 minimum, AISI 316/A4 for coastal installations) to prevent mineral staining. Maintain minimum 20mm edge distance and 40mm end distance.

Installing PaCS® Hidden Fastening System

The simplest installation method for PaCS® profiled boards:

• Connect PaCS Strip fasteners together along the joist line
• Secure strips firmly to joists using appropriate fasteners
• Simply snap decking boards onto the clips—no additional fixing required
• System automatically maintains uniform 5mm spacing and ventilation
• No screwing required for individual boards

Installing TENI Clip System

For D34 profiled boards requiring edge-grooved preparation:

• Ensure boards are properly edge-grooved (factory or site preparation using biscuit jointer)
• Position first board at deck edge with appropriate overhang
• Insert TENI clip into board groove and secure to joist with supplied stainless steel screw
• Slide next board into position, engaging with clip groove
• System maintains consistent 6mm gaps throughout
• For aluminium joists other than RELO T, use specialized self-tapping screws or pre-drill pilot holes

Installing Face Screwed Thermo-Treated Decking

Traditional installation offering maximum board contact:

• Always pre-drill and countersink all screw holes to prevent splitting
• Use stainless steel screws exclusively (AISI 304 minimum, AISI 316/A4 for coastal areas)
• Maintain minimum 3-4mm gaps between boards, or 16mm where boards meet walls
• Minimum edge distance: 20mm from board edge
• Minimum end distance: 40mm from board end
• Countersink screws flush or maximum 2mm below surface
• Avoid over-tightening which can damage the timber

Board Spacing and Movement

Thermo-treated timber offers superior dimensional stability:

• PaCS® system: automatic 5mm gaps
• TENI system: automatic 6mm gaps
• Face screwing: minimum 3-4mm gaps between boards
• 16mm gaps where boards meet walls or structures
• Minimal expansion and contraction compared to untreated timber

Ventilation and Sub-Frame Requirements

Critical ventilation prevents moisture accumulation and ensures longevity:

• Install joists at maximum 400mm centre-to-centre spacing
• Minimum 50mm air space beneath decking
• Adequate cross-ventilation to allow moisture to escape
• Proper drainage with sloped ground surface where decks are close to ground level
• Avoid any design that traps moisture beneath the deck
• Use pressure-treated softwood or aluminium joists
• Metal subframes should incorporate wooden skins to prevent thermal movement issues

Species-Specific Characteristics

Thermo-Treated Ash Exceptionally high-value timber with smooth finish and rich, deep brown colour. Superior hardness makes it ideal for high-traffic deck areas. The modification process enhances ash’s natural density while eliminating tendency to warp.

Thermo-Treated Pine Features distinctive knotted character with attractive golden-brown tones. Excellent durability at a more accessible price point. The thermal process dramatically improves pine’s outdoor performance for demanding exterior applications.

Professional Installation Tips

Use carbide-tipped blades and router bits as thermal modification hardens wood fibres. Always wear dust masks and eye protection. Deck boards should span minimum three joists. Use a decking wrench to straighten boards before final fastening. Seal all cut ends immediately with wax emulsion end grain sealant to prevent moisture infiltration and end checking.

Need Help?

While professional installation is advised for best results, we’re here to support DIYers with installation advice and technical guidance. Contact us for tailored support to suit your project.

Overview: Thermo-Treated Timber Decking and Cladding

Thermo-treated (thermally modified) timber offers exceptional performance for outdoor applications, combining natural beauty with enhanced durability and stability. The thermal modification process uses only heat, steam, or pressure to alter wood at a cellular level, creating a chemical-free, high-performance material that resists rot, decay, and dimensional movement. With proper care, thermo-treated decking provides decades of reliable service while maintaining authentic wood character.

Understanding Thermal Modification

The thermal modification process involves heating wood to high temperatures in a controlled environment without using chemicals:

• Removes sugars and resins that attract fungi and insects
• Creates dimensionally stable timber with reduced moisture absorption
• No chemicals or hazardous substances used
• Results in rich brown colouration throughout entire board thickness
• Environmentally friendly alternative to pressure-treated or tropical hardwoods

Performance Advantages

Superior Stability

• Reduces dimensional movement by up to 50%
• Less expansion and contraction due to moisture changes
• Minimal warping, cupping, or twisting
• Maintains straight, level surfaces throughout service life

Enhanced Durability

• Achieves Durability Class 1 (25+ years) or Class 2 (15+ years) depending on species
• More resistant to rot, decay, and insect damage
• Thermo-ash comparable to tropical hardwoods with 25+ year lifespan
• Protection extends through entire board thickness

Additional Benefits

• Chemical-free process generates no hazardous waste
• Doesn’t accumulate heat like composites, feels pleasant underfoot
• Smooth, splinter-free surface
• Sourced from sustainably managed forests

Natural Weathering Process

• Rich brown colour from thermal modification; silver-grey from natural aging
• Surface fades to silver-grey starting immediately after installation
• With direct sunlight, may age to silver in as little as 6 months
• Wood ages unevenly so different sides discolour at different rates
• Colour change doesn’t affect durability or structural performance
• Quick power wash can restore wood toward original colour

Routine Maintenance

Regular Cleaning

• Sweep regularly to remove debris and prevent surface staining
• Clean with mild soap and water as needed
• Keep surface free of leaves, needles, and moisture-retaining debris
• Remove spills, organic matter, and standing water promptly

Stain and Surface Management

• Most stains from barbecue spills, beverages, and general use fade naturally
• Household chemicals, grilling stains, wine, and sauces can leave surface stains
• Light sanding removes silvery surface and restores original appearance
• Deeper scratches can be blended with light sanding
• Sanded areas will weather to match surrounding boards

Annual Tasks

• Inspect and tighten fasteners
• Check for damage or wear
• Ensure proper drainage and ventilation
• Maintain clearance around edges to promote airflow
• Remove vegetation growth promptly

Colour Preservation Options

Option 1: Natural Silver-Grey Patina

• Allowing wood to age naturally requires very little maintenance
• Simply keep deck clean and enjoy 25+ years of low-maintenance beauty
• More economical, eco-friendly choice
• Authentic weathered wood aesthetic

Option 2: Maintain Rich Brown Tones

• Apply UV-resistant penetrating oil annually to preserve darker tone
• For direct sun exposure, reapplication may be needed sooner
• Products like CUTEK Extreme provide deep penetration
• Reapplication typically required every 12-18 months depending on exposure
• Maintaining brown colour requires more time and effort

Protective Treatment Application

For best results, prefinish boards with penetrating UV protectant oil before or immediately after installation:

Initial Treatment

• Factory finishing strongly recommended to protect all 6 sides
• Initial coating allows wood to age evenly and protects from trapped moisture
• Factory finishing with penetrating oil helps reduce checking and cracking
• Apply to clean, dry, dust-free surfaces

Ongoing Maintenance

• Clean surface with wood brightening cleaner before oil application
• If power washing, use lowest setting and widest fan, wait 1 day before oiling
• Sand surface before first reapplication if needed
• For grey boards, use colourless oil without UV filter to preserve tone
• Reapply according to manufacturer recommendations

Long-Term Performance

Expected Lifespan by Species

• Thermo-ash: Durability Class 1, 25+ years (comparable to tropical hardwoods)
• Thermo-spruce: Durability Class 1, 25+ years
• Thermo-pine: Durability Class 2, 15+ years when properly maintained
• Premium Nordic species can exceed 30 years with proper care
• Quality manufacturers offer 20-year limited warranties

Performance Factors

• Quality of thermal modification process
• Proper installation and ventilation
• Regular cleaning and debris removal
• Environmental exposure levels
• Maintenance frequency
• Untreated softwoods degrade within few years; thermally modified versions last 15-25+ years

Installation Considerations

• Use thermally modified timber for substructure to match decking lifespan
• Follow manufacturer’s installation guidelines
• Ensure adequate ventilation beneath structure
• Proper installation ensures deck can withstand elements
• Consider hidden fixing systems for clean appearance

Maintenance Schedule Summary

Upon Installation

• Apply UV-protective oil if colour preservation desired
• Ensure proper drainage and ventilation

Ongoing (As Needed)

• Sweep and clean regularly
• Clean spills promptly
• Remove vegetation immediately

Annual Tasks

• Inspect and tighten fasteners
• Check for damage
• Reapply UV oil if maintaining brown colour (more frequently in high-sun areas)
• Verify clearance and airflow

Every 12-18 Months (If Preserving Colour)

• Clean surface thoroughly
• Light sand if needed
• Reapply UV-protective treatment

Cost-Benefit Analysis

• Higher initial investment than untreated timber
• Often more budget-friendly than tropical hardwood alternatives
• Significantly lower maintenance requirements
• No chemical treatments required throughout lifespan
• Exceptional durability makes it cost-effective long-term investment
• Reduces replacement and maintenance expenses

Best Practices Summary

• Thermo-treated boards don’t necessarily require surface treatment, but regular oiling refreshes appearance
• Clean regularly to prevent debris accumulation
• Choose maintenance approach based on desired aesthetic
• Apply UV treatments annually if preserving colour
• Maintain proper ventilation and clearance
• Follow manufacturer guidelines for optimal results

Need Help?

Thermo-treated timber offers the perfect balance of natural beauty, exceptional performance, and environmental responsibility—providing you with a low-maintenance outdoor space that lasts for decades. For product recommendations, treatment advice, or technical support, our experienced team is always on hand to assist. Contact us for tailored guidance to suit your project.