Outdoor LivingFebruary 22, 2024 15 min read

How to Maintain Your Outdoor Decking in Cornwall

Cornish weather can be tough on timber. Here are our top tips for treating, cleaning, and maintaining your decking so it lasts for years.

Why Cornwall's Climate Is Tough on Decking

Cornwall's climate is, to put it kindly, characterful. We enjoy more sunshine hours than much of the UK, but we also endure salt-laden coastal winds, driving rain, and humidity levels that swing wildly through the year. For timber decking, this combination is genuinely challenging.

Salt spray accelerates the corrosion of fixings and the degradation of finishes. Persistent moisture encourages algae and rot. UV exposure, intensified by reflection off the sea, bleaches and breaks down surface treatments. A deck that is perfectly maintained inland can deteriorate noticeably faster a few hundred yards from the coast.

Understanding these specific challenges is the first step to overcoming them. The maintenance regime that suits a sheltered inland deck will not be enough for a coastal one, and the products that work in a dry climate may fail quickly in ours. This guide is written specifically for Cornish conditions.

Choosing the Right Decking in the First Place

The best maintenance is choosing a decking material suited to your location from the outset. For coastal Cornish gardens, we generally recommend either sustainably sourced hardwood (such as iroko or balau) or high-quality composite decking. Both resist moisture, rot, and salt far better than softwood.

Softwood decking, typically pressure-treated pine, is the most affordable option and is perfectly serviceable in sheltered inland gardens with diligent maintenance. Near the coast, however, its higher moisture uptake and softer surface make it a less durable choice, and it will require more frequent treatment to stay sound.

Composite decking, made from a blend of recycled wood fibres and plastic, has become increasingly popular in Cornwall precisely because it addresses our climate's challenges. It does not rot, splinter, or require regular oiling, and modern composites look far more natural than earlier generations. The trade-off is a higher upfront cost and a warmer surface in direct sun.

The Annual Maintenance Routine

Whatever your decking material, an annual maintenance routine keeps it in good condition and catches problems early. We recommend scheduling this for late spring, when the worst of the winter weather has passed and the deck has dried out enough to work on.

Begin with a thorough clean. Sweep away all debris, then wash the surface with a specialist decking cleaner or a mild detergent and a stiff brush. A pressure washer can be used with great care — keep the nozzle at least 30cm from the surface and use a wide fan jet — but excessive pressure will damage timber fibres and should be avoided.

Allow the deck to dry fully, which in Cornwall can take a day or two depending on the weather. Once dry, inspect for any loose boards, raised fixings, or signs of rot, and address these before proceeding to treatment. A small problem caught now is a cheap fix; the same problem left for a year can mean replacing a whole board.

Treating Timber Decking

For timber decking, the annual treatment is the single most important maintenance task. The right product depends on the look you want and the level of protection you need. Decking oils penetrate the timber, nourishing it and bringing out the natural grain, but they need reapplying every year. Decking stains sit on the surface and offer colour as well as protection, typically lasting two to three years. Decking paints offer the most opaque finish and the longest intervals between coats, but they will eventually peel and require stripping.

In coastal Cornwall, we favour high-quality decking oils for hardwood decks, reapplied annually, because they allow the timber to breathe and do not trap moisture. For softwood decks, a semi-transparent stain offers better protection and a longer interval between treatments, which is valuable given softwood's greater vulnerability.

Always apply treatment to clean, dry timber, and avoid applying in direct hot sun or when rain is forecast within 24 hours. Two thin coats are always better than one thick one, as they penetrate and adhere more effectively. Pay particular attention to the end grain of each board, where moisture enters most readily.

Preventing and Treating Algae

Algae is the most common decking problem in Cornwall, particularly on north-facing or shaded decks that stay damp for long periods. It presents as a green or black slimy film that is not just unsightly but genuinely dangerous when wet, making the deck surface treacherously slippery.

Prevention starts with design. A well-built deck should have a slight fall to shed water, gaps between boards for ventilation, and ideally some exposure to sunlight. If your deck is shaded by trees, consider thinning the canopy to let in more light and air. Keeping the deck clear of leaf litter, which traps moisture and feeds algae, is also essential.

Where algae has taken hold, treat it with a specialist algae and moss killer, then scrub with a stiff brush. A pressure washer on a low setting can help, but be cautious of damaging the timber. Once clean and dry, applying a fresh coat of treatment will help prevent recurrence. In persistently damp spots, an anti-slip decking treatment, which adds a fine grit to the surface, is a worthwhile investment for safety.

Inspecting and Replacing Boards

Even well-maintained decking will eventually need board replacement, and catching this early prevents damage to the substructure. During your annual inspection, look for soft spots, particularly around fixings and at the ends of boards, and probe any suspect areas with a screwdriver. Timber that is soft or spongy is rotting and should be replaced.

Also check the substructure. Joists are less exposed than the decking but are not immune to rot, particularly where they meet the ground or where water can sit. A rotting joist is a more serious problem than a rotting board, as it compromises the whole structure, so any softness here should be addressed promptly.

When replacing boards, use the same species and, ideally, the same batch to ensure a consistent appearance. New boards will weather to match the existing decking over a season or two. Always use corrosion-resistant fixings — stainless steel is essential in coastal Cornwall — to prevent the staining and failure that cheaper fixings cause.

Composite Decking: Lower Maintenance, Not No Maintenance

A common misconception is that composite decking is maintenance-free. It is not — it is lower maintenance. Composite does not need oiling, staining, or painting, and it will not rot or splinter, but it still requires regular cleaning to look its best and to prevent the build-up of algae and dirt.

Clean composite decking at least once a year with a specialist composite cleaner and a soft brush. Avoid pressure washing on high settings, which can damage the surface texture, and never use solvents or abrasive cleaners. Pay attention to the gaps between boards, which can clog with debris and impede drainage.

One issue specific to composite is heat. In direct summer sun, darker composite boards can become uncomfortably hot underfoot. If this is a concern, lighter colours stay cooler, and there are now composite ranges specifically engineered to reduce heat absorption. We can advise on the best options for sun-exposed Cornish gardens.

Winter Protection

Cornish winters are wet rather than deeply cold, but they are long, and the persistent damp is harder on decking than a short, sharp freeze. The most important winter protection is keeping the deck clear. Leaf litter, plant pots left in the same spot all winter, and accumulated debris all trap moisture against the timber and accelerate decay.

Move plant pots regularly to prevent moisture build-up beneath them, and sweep the deck clear of leaves weekly through the autumn. If snow does fall, brush it off rather than letting it sit and melt slowly into the timber. Avoid using salt or chemical de-icers, which can damage both timber and composite surfaces.

A well-maintained deck will come through a Cornish winter in good shape and need only a clean and refresh in the spring. A neglected one will show the effects of a single wet season, and the cumulative damage over several winters can be significant. Consistency, rather than intensive effort, is the key.

When to Call a Professional

Much decking maintenance is well within the scope of a competent homeowner, but some situations call for a professional. Extensive rot, structural movement, or a deck that has become dangerously slippery despite treatment are all best assessed by someone who understands both the materials and the Cornish climate.

We are always happy to inspect a deck and advise on what it needs, whether or not we built it originally. Sometimes a simple treatment is enough; sometimes a partial rebuild is more economical in the long run than repeated repairs. An honest assessment is worth more than a guess, and it costs nothing to ask.

Ultimately, a deck is an investment in your enjoyment of your garden, and like any investment it rewards care. With the right material, the right maintenance, and a little Cornish common sense, a quality deck will give you fifteen or twenty years of pleasure — far longer than most people expect.

Frequently Asked Questions

Quick answers to the questions we hear most about How to Maintain Your Outdoor Decking in Cornwall.

How often should I treat my timber decking in Cornwall?+

Hardwood decks should be oiled annually, while softwood decks treated with a stain typically need re-coating every 2–3 years. Coastal locations may require more frequent treatment due to salt exposure.

Is composite decking really maintenance-free?+

No — composite is lower maintenance, not maintenance-free. It needs no oiling or staining but should be cleaned at least annually with a specialist composite cleaner and a soft brush.

How do I stop my decking going green and slippery?+

The green film is algae, common in damp, shaded Cornish gardens. Improve light and ventilation, keep the deck clear of debris, treat with an algae killer, and consider an anti-slip treatment for persistently damp areas.

Can I pressure wash my decking?+

Yes, but with care. Keep the nozzle at least 30cm away, use a wide fan jet, and avoid high pressure, which damages timber fibres. Never pressure wash composite decking on a high setting.