A slippery deck is one of the most common complaints we hear from homeowners around Bolton once the clocks go back. The good news is that the slipperiness almost never comes from the boards themselves, and with the right cleaning routine and a couple of inexpensive additions you can keep your decking safe to walk on right through to spring.
Timber decking is not naturally slippery, even when wet. What makes it dangerous is the thin film of algae, mould and general grime that builds up on the surface through autumn and winter. In the North West we get somewhere in the region of 140 to 150 wet days a year, and shaded, north facing decks can stay damp for weeks at a time, which is exactly the environment algae loves.
Fallen leaves make things worse. Left sitting on the boards, they break down into a greasy layer that traps moisture underneath and feeds the algae. So the single most effective habit is also the simplest: brush leaves and debris off the deck every week or two from October onwards, paying attention to the gaps between boards where muck collects.
A stiff broom and a bucket of warm water with a decking cleaner or a diluted algae remover will shift most of the film. Work along the grain of the boards, leave the solution to sit for the time stated on the product, then rinse thoroughly. For a typical 15 to 20 square metre deck this is a couple of hours of work, and doing it once in late autumn and once mid winter is usually enough.
Be careful with pressure washers. On a low setting, held at an angle and kept moving, they are fine on hardwood and composite. On softwood, a powerful jet up close will tear out the softer grain, leaving a furry surface that actually holds water and algae better than before. If your boards are already ridged and grooved, a jet wash can also force grime deeper into the grooves.
Even a clean deck can be slick after a frost, so it is worth adding physical grip on the routes you actually use, typically the path from the back door to the shed, bin store or washing line. Anti slip strips made of aluminium with a gritted surface screw straight onto the boards and cost roughly 10 to 20 pounds per board length. They are the most reliable fix we know and they work in ice as well as rain.
Alternatives include anti slip decking tape, which is cheaper but tends to peel within a season or two on damp timber, and rubber or gritted stair treads for steps, which are the highest risk spot on any deck. If you are oiling or staining the deck anyway, look for a product with added anti slip aggregate. It gives a modest improvement across the whole surface rather than a strong one in specific places.
If your deck stays wet for days after rain, the problem may be underneath rather than on top. Decks built too close to the ground with poor airflow, or with boards laid dead level rather than with a slight fall of around 1 in 100, hold water and will green up no matter how often you clean them. Improving ventilation under the frame or adjusting the fall is a bigger job, but it deals with the cause instead of the symptom.
If you are at the point of replacing the deck, it is worth knowing that modern composite boards with a deeply textured or wood grain finish hold their grip far better in winter than smooth softwood, and they do not support algae growth in the same way. They cost more up front, typically two to three times the price of treated softwood depending on the brand and the size of the deck, but the winter maintenance drops to an occasional wash.
On icy mornings people understandably reach for the same rock salt they use on the drive. On timber decking, use it sparingly. Salt draws moisture and can accelerate corrosion of screws and fixings, and coarse grit gets ground into the boards underfoot. A light scattering of plain sand gives temporary grip without the downsides, and it sweeps off easily once the thaw comes.
Whatever you use, clear it off once the ice has gone. Anything left sitting on the boards through a wet week becomes part of next month's slippery film.
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