How to Stop Composite Decking Becoming Slippery in Wet Weather

If you've had timber decking in a UK garden, you'll know the drill: the first wet morning of autumn, someone nearly goes over, and the annual scrubbing session begins. It's one of the reasons so many homeowners switch to composite decking. But does composite automatically solve the problem? Not always — and understanding why composite decking becomes slippery in wet weather is the key to making sure yours stays safe all year round.

At Duralive Decking, we've installed plenty of composite decking projects across Merseyside and Cheshire. This guide explains what causes slippery decking, how composite boards handle wet conditions compared to timber, and what you can do — whether you're planning a new deck or trying to make an existing one safer.

Why Does Decking Become Slippery in Wet Weather?

Slippery decking isn't just about rain falling on a flat surface. It's a combination of factors that build up over time, and each one tends to compound the others.

Surface texture plays the biggest role. Smooth board surfaces offer very little grip when wet. The rougher and more textured the board surface, the more friction it provides underfoot — which is why board choice is so important from the outset.

Algae and moss growth is the other major culprit in the UK. Shaded or poorly ventilated decking can quickly develop a thin film of algae or moss that is almost invisible to the eye but creates a dangerously slippery surface, particularly in autumn and winter when the deck is used less frequently and cleaned less often.

Standing water makes both problems significantly worse. Poor drainage allows water to pool on the deck surface, reducing grip and accelerating algae growth. Organic debris — leaves, pollen, garden waste — breaks down into a slick layer that won't wash away on its own.

Understanding these causes means you can tackle the problem at the source, rather than reacting after someone slips.

Does Composite Decking Get as Slippery as Timber?

Composite decking is significantly safer in wet weather than untreated timber, but it isn't immune to becoming slippery. The two materials behave very differently — and once you look at the published data, the gap is substantial.

Timber decking that hasn't been treated, stained, or sealed becomes extremely slick when wet and is particularly prone to rapid algae and moss growth. As the wood ages, the grain opens and gives algae more places to establish. If you've ever slid across an old wooden deck in October, you'll know how unforgiving it can be.

Premium composite boards are engineered to perform very differently — and the manufacturers we install at Duralive publish independent slip resistance data to prove it.

How slip resistance is measured

In the UK, slip resistance is most commonly assessed using the Pendulum Test set out in BS 7976-2. This is the method the Health and Safety Executive (HSE) recommends for evaluating slip risk on floor surfaces. It produces a Pendulum Test Value (PTV):

• 36 and above — low slip potential

• 25 to 35 — moderate slip potential

• 24 and below — high slip potential

Some manufacturers also publish results against DIN 51097, the European ramp test for wet barefoot areas, which classifies surfaces from Class A (lowest grip) to Class C (highest — the standard required for swimming pool surrounds and similar wet barefoot environments).

Here is how the three brands we regularly install compare against those benchmarks.

Millboard

Millboard tests its decking to BS 7976 using the Pendulum method. The Enhanced Grain range — the deeply embossed surface that replicates natural timber — records 49–60 PTV dry and 36–42 PTV wet, comfortably above the HSE's low-risk threshold.

The Lasta-Grip range pushes that further. Designed for poolside, commercial, and high-risk environments, Lasta-Grip boards combine the Lastane® polyurethane surface with integrated grit inserts. Millboard's published figures for the Carbonised Charred boards reach 77 PTV dry and 55 PTV wet, with the Emberred colour hitting 92 PTV dry and 73 PTV wet — among the highest documented figures for any composite deck board on the UK market.

Trex

Trex publishes its slip resistance data against prEN 15534-1 using the DIN 51097 ramp test for wet barefoot areas. Both Trex Transcend and Trex Enhance achieve Quality Class C — the highest classification available under that standard, used for areas around swimming pools, communal showers, and other wet-loaded barefoot surfaces. Transcend recorded an average inclination angle of 28°, with Enhance at 32°, both well inside Class C territory.

NewTechWood

NewTechWood tests its UltraShield range to BS 7976-2:2002 using the Pendulum method with the Slider 96 (the standard rubber slider for shod pedestrian testing). The UH06 board recorded an average wet PTV of 37, placing it in the HSE's "low slip potential" classification. The same boards are separately rated R10 under DIN 51130, the German ramp test for shod surfaces.

What this means on a real deck

Published test figures are recorded in laboratory conditions on new, clean boards. A freshly installed deck will perform at or close to those values when it's handed over — but slip resistance isn't a fixed property for the life of the deck.

PTVs fall over time as boards accumulate dirt, organic debris, and biofilm — particularly in shaded or poorly ventilated areas. A board that scored 38 in the lab can drop into the 20s after a couple of badly maintained winters, which is precisely how a "non-slip" deck ends up sending someone over.

The principle is the same whichever brand you choose: specify a board with strong published data, install it correctly with proper drainage and airflow, and keep it clean. That combination is what keeps a deck safe long after the warranty paperwork has been filed.

How to Prevent Composite Decking from Becoming Slippery

Prevention is far more straightforward than dealing with a slippery deck after it has developed a problem. These are the factors that make the biggest difference.

Choose the Right Board for Your Environment

Not all composite boards offer the same level of grip. When choosing decking, look for a deeply embossed or textured surface rather than a smooth or lightly brushed finish, and check whether the manufacturer provides anti-slip performance data. If your deck will be shaded, north-facing, or in a particularly damp location, prioritise boards with higher grip ratings and algae-resistant surface technology.

See our Composite Decking page covers the composite board brands we install, including Millboard, Trex, and NewTechWood — all of which offer textured, grip-focused surfaces suited to the UK climate.

Get the Drainage Right During Installation

A deck that drains effectively dries faster after rain and is far less likely to develop algae. During installation, this means maintaining a slight fall of around one to two percent away from the house, using hidden fixings that leave an appropriate gap between boards for drainage and airflow, and avoiding laying boards over ground that retains water or has very limited ventilation underneath.

Poor drainage is one of the most common problems we see on decks installed elsewhere. If water sits on your deck surface after rain rather than running off, the surface stays wet for longer and algae will follow. Our case studies include projects where we've addressed drainage problems as part of a full deck replacement.

Keep the Surface Clean Regularly

Composite decking requires far less maintenance than timber, but it does need periodic cleaning — particularly to prevent algae and moss from establishing. The routine for most composite boards is straightforward: brush away leaves and organic debris regularly (not just once a year), wash the surface with warm soapy water and a stiff-bristle brush working along the board grain, then rinse thoroughly with clean water.

For algae or moss that has already taken hold, a purpose-made composite decking cleaner will be considerably more effective than soap and water alone. Avoid bleach-based products unless the board manufacturer specifically recommends them, as these can damage the surface finish and affect colouration over time.

What to Do If Your Existing Composite Deck Is Already Slippery

If your current decking has become slippery, the right fix depends on identifying the underlying cause.

If there is visible algae or moss growth, a thorough clean with a composite-approved cleaner should make an immediate difference. Follow up with more regular cleaning going forward to prevent regrowth.

If the surface texture itself has worn smooth — which can happen on older or lower-quality boards after several years — cleaning will not restore grip. The surface has degraded beyond what maintenance can address, and replacement is the long-term solution.

If water is pooling on the deck surface after rain, the issue is structural or installation-related. A professional assessment can determine whether the drainage can be improved or whether the deck needs to be reinstalled to the correct specification.

Shaded spots — next to fences, under pergolas, or against north-facing walls — will always dry more slowly than open areas of the deck. These spots may need more frequent cleaning or a board with higher anti-slip performance to compensate.

Are Anti-Slip Strips Worth Adding to Existing Decking?

Anti-slip strips — typically adhesive rubber or aluminium strips applied across board surfaces — can be added to existing decking as a retrofit measure. They provide meaningful grip in targeted high-risk areas: steps, ramps, or sections regularly used by elderly family members or young children.

As a whole-deck solution, however, they are cumbersome to apply uniformly, can look out of place, and need periodic replacement. If you're considering anti-slip strips across an entire deck surface, it usually indicates that the original board choice or installation was not right for the environment. A well-specified composite deck with proper drainage should not require retrofitted grip across the main deck area.

Safe, Slip-Resistant Composite Decking Starts with the Right Choices

The most effective way to prevent composite decking becoming slippery in wet weather is to get the fundamentals right from the beginning — choosing a board engineered for grip, ensuring proper drainage is built into the structure, and establishing a regular cleaning routine. Retrofitting safety measures onto a poorly specified deck will always be a compromise.

If you're planning a new composite deck and want it specified correctly for a UK climate, or if you have an existing deck that has become unsafe, get in touch with the team at Duralive Decking. We install Millboard, Trex, and NewTechWood across Merseyside and Cheshire, and we're happy to advise on the right solution for your garden.