Native hardwoods are classed on a durability table according to their resistance to weathering and rot, fungal or insect attack. The higher the class - the more durable the timber. When you chose a timber to perform as a decking platform - be aware that it is the most exposed structural element in residential building. It is recommended you chose a species that is either Class 1 or Class 2 based upon in-ground Durability. Both classes will provide a minimum 25 years service if the deck is elevated and well ventilated underneath.•Timber Service Life Design Guide 5If the deck is closer to the earth than 300mm - or is poorly ventilated and approaches ground level on one or two sides, then choose only a Class #1 Durability timber.The greater part of the recycled durable hardwood inventory may be more suitable milled to flooring or joinery board rather than to a decking product because of fine drying check and other penetration features found in air-dried timbers. These features are a visual attribute in timbers used for an interior purpose - but can represent a defect on the upper face of decking boards. Rather than dock and grade heavily, recyclers typically avoid milling these timber batches for decking. The benchmark in suitability would be the kiln-dried new forest product in decking grade - but never less suitable.Best use of available dimension is another consideration. Found dimensions of salvaged timber suggest particular uses. Recyclers are unlikely to re-saw 200mm board into narrower dimensions for decking because overall value is somewhat reduced. These necessary economies of recycling will govern the use of recycled timber for decking as much as suitability. In consequence, new kiln-dried timbers may have a significant price and suitability advantage in outdoor use - particularly in the small section sizes (19-25mm) that suit decking board. Whereas recycled timbers have a suitability advantage over new timber for posts and beams since kiln drying is not possible when thickness of beam exceeds 50mm. Green timbers that exceed 20% MC are prone to shrink, warp and split in full-sun to a degree dependent on species, section, sawlog character as well as treatment of surface and end-grain.New Decking and Cladding timbers should be kiln-dried to provide stability. The moisture content for outdoor timbers can be slightly higher than for furniture - at 15-16% MC (moisture content). Narrow decking boards - 65mm or 86mm wide boards - are preferable if installing standard 19mm thick decking. These widths are preferred because the balance of width to thickness provides stability in full sun. As a rule of thumb, try not to exceed 5:1 in ratio. All decking boards will still cup or dish slightly on the top surface regardless of species or fixings. The wider the surface - the more pronounced the surface distortion. This will be minimised with regular oiling. 135mm wide decking is popular nowadays - but in decks exposed to full sun and rain opt for 25-32mm thickness for added stability and install 135 x 19mm only for covered verandas, outdoor walls or enclosed decks. Decks can develop a black or green mould build up on the upper face months or years after installing - especially on the shaded side of the building. Pressure-washing on its own will remove mould - and re-oiling with penetrating decking oil slows its return.Avoid harsh acidic or alkaline commercial deck clean products. Deck-wash products can affect the protective plating on metal screws and nails and cause rust halos to develop in the timber around fixings. Misuse of these products accelerates weathering and shortens the natural life of the decking timber. If using posts in-ground for fences and gates - ensure they are Class 1 Durability. For decks and pergolas, avoid direct contact of structural timbers with the ground - as this practice will provide a bypass to existing termite barriers and protection. Timber posts should be stirruped in a concrete footing - the base of the post clear of contact with soil. In this event Class 1 or 2 timbers may be used.
recycled timber outdoors - decking, cladding and pergolas