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PRICES EXCLUDED VAT
Price Linear Meter (lm)
Price Meter Squared (m2)
Board Thickness
Board Full Width
Timber Species
Board Profile
Grade
These ThermoWood grooved decking boards are machined specifically for secret fix installation using BROfix hidden decking fasteners. No screws on the board face, no rusting fixings, no visible hardware — just a clean, continuous deck surface from edge to edge.
At 26x117mm, these boards offer a solid face width for residential and commercial decking. The grooved profile accepts BROfix clips at each joist position, with the clip then concealed beneath the next board as you work across the deck. The result is a professional finish that is as practical as it looks — secret fix installation also reduces the total number of screws required by around half compared to face-fixing.
| Specification | Detail |
|---|---|
| Species | Thermally Modified Pine (ThermoWood) |
| Profile | Grooved — BROfix secret fix compatible |
| Dimensions | 26 x 117 mm |
| Surface finish | Smooth both faces |
| Fixing method | Secret fix / Hidden fix (BROfix clips) |
| Modification class | Thermo-D |
| Durability class | Class 1–2 |
| Maintenance | Low — no annual treatment required |
| Supply | UK nationwide |
Secret fix decking eliminates visible screws from the board face entirely. A hidden clip locates into the groove along the edge of each board and is fixed down to the joist with a single screw. The next board slides over the clip, concealing it completely. Repeat across the deck and the finished surface has no exposed fixings at all.
Beyond the aesthetic benefit, secret fixing holds boards flat along their full length rather than pulling them down at two points per joist span. Combined with the automatic 6 mm expansion gap that BROfix clips set between every board, the system accommodates the natural seasonal movement of timber without cupping, buckling, or gapping.
Dimensional stability matters more with secret fix than with face-fixed decking. If boards warp or cup after installation, the hidden clips are placed under lateral stress and the flat surface you paid to achieve is compromised. ThermoWood is thermally modified pine — treated above 180°C without chemicals — which permanently reduces its ability to absorb and release moisture. The boards move significantly less across the seasons than untreated softwood, keeping the deck flat and the fixing system performing as designed year after year.
ThermoWood also reaches a natural durability of Class 1–2, meaning it performs outdoors without chemical preservative treatment. It is a genuinely low-maintenance decking material, well suited to full UK weather exposure.
These boards are designed for use with BROfix hidden decking fasteners — sold separately in packs of 300, used at 2.2 clips per linear metre. For 26x117mm boards, divide your deck area (m²) by 0.117 to get total linear metres, then multiply by 2.2 and add 10% for wastage.
Use stainless steel A2 screws — 4.2 x 42 mm, Torx 20 head — to fix the BROfix clips to the joists. Do not use zinc-plated or galvanised screws with ThermoWood as they can cause surface staining.
Download the full installation guide: BROfix Hidden Decking Fasteners — Installation Guide (PDF)
ThermoWood requires no treatment to maintain its structural integrity outdoors. Left untreated, the boards will silver to a uniform grey over time. To retain the warm brown tone, apply a UV-stable decking oil before installation and reapply periodically. We stock Remmers and Koopmans wood oils and stains that are well suited to ThermoWood decking.
Always seal cut ends with a suitable end-grain sealer or decking oil immediately after cutting to limit moisture uptake at exposed grain.
Secret fix decking uses hidden clips that locate into the groove of each board and are screwed to the joist below. The next board covers the clip, leaving no visible fixings on the deck surface. It gives a clean, contemporary finish with no exposed screw heads.
These boards are designed for use with BROfix hidden decking fasteners. Each clip automatically sets a 6 mm expansion gap between boards. BROfix clips are sold in packs of 300 at 2.2 clips per linear metre.
ThermoWood's thermal modification greatly reduces moisture movement compared to untreated softwood. This stability is critical for secret fix decking — boards that warp after installation stress the hidden clips and compromise the flat finish. ThermoWood keeps the system performing as designed.
No treatment is required to maintain structural performance. Left untreated the boards will silver naturally. To retain the warm brown colour, apply a UV-stable oil before installation. We stock Remmers and Koopmans wood oils suitable for ThermoWood.
BROfix clips are used at 2.2 per linear metre. For 26x117mm boards, divide your deck area in m² by 0.117 to get linear metres, then multiply by 2.2. Add 10% wastage. BROfix clips are sold in packs of 300.
Add these boards to your basket above and pick up your BROfix hidden decking fasteners at the same time. For a full quote including boards, clips, fixings, and woodcare — contact our team.
Thermowood, Nordic Spruce, Siberian Larch, Charred TImber (Shou Sugi Ban Technique)