Composite decking is one of the most durable and low-maintenance alternatives to traditional timber, but like any outdoor material, it performs best when installed and cared for correctly. While it won’t rot, splinter, or attract termites like wood, poor drainage, improper spacing, or neglecting routine cleaning can still reduce its lifespan or impact its appearance.
Poor drainage on deck surface
When water cannot flow freely off the deck, it sits on the surface and leaves dirt marks that require unnecessary cleaning. Composite boards resist rot whereas timber is well known to rot from water and more so from constant exposure to standing water. Checking for blocked gaps and ensuring boards are laid with the correct slope helps water run off rather than pool. For a truly durable solution, it’s worth comparing timber with a WPC composite decking product to find the right profile for your climate.
In areas with frequent rain, the risk of moisture damage increases if drainage channels become clogged with debris. Leaves or dirt that accumulate in the gaps between boards hold moisture against the plastic-wood core. This trapped dampness encourages mould growth and staining on the deck surface. A simple cleaning routine every few months can clear debris and improve water flow.
Some composite boards feature a hollow core that is more vulnerable to moisture entry through cut ends or damaged sealing. If water infiltrates the inner cavities, it may take longer to dry out, leading to internal damage. Applying end-cap sealing products designed for your board profile can protect cut ends and ensure any rainwater drains away quickly.
Standing water pooling between boards
When boards are spaced less than 3mm, rainwater can collect and combined with general rubbish (such as leaves) remain between the boards. This standing water affects the hidden fixing system and may cause fasteners to corrode, reducing deck stability. Checking board spacing against manufacturer guidelines and using the correct hidden clip spacing keeps gaps uniform and allows drainage.
Pooling water also encourages a damp, shaded environment where algae and mould thrive. These organisms create a slippery surface that risks injury and detracts from the deck’s appearance. Regularly rubbing affected areas with a stiff brush and a mild cleaning solution removes early growth before it takes hold.
If pooling persists despite proper spacing, inspect the supporting joists and sleepers for joist warping or settling that might tilt the deck surface. Uneven joists can trap water even when the boards themselves are installed correctly. Replacing or shimming the joists restores the intended slope and prevents future pooling. It’s important to note that composite decking rarely ‘bows’ or ‘warps’. If this occurs, it is easily corrected during installation, and the boards will perform as expected.
High humidity and trapped moisture
In coastal or subtropical regions, high ambient humidity keeps the deck surface damp long after rain. Composite decking is designed to tolerate moisture, but it performs best in well-ventilated conditions. Ensuring sufficient airflow beneath the deck prevents moisture from lingering under the boards and causing mould on the underside.
Trapped moisture beneath planters, outdoor rugs or furniture bases may also harm the deck over time. These items block air circulation and create micro-environments for mould and mildew to form. Placing furniture on pads or slightly lifting planters avoids direct contact and lets air flow freely.
During installation, adding ventilation gaps between the ground and deck joists is essential. Even a small clearance promotes airflow under the deck, drying out any moisture that seeps through board gaps.
Sunlight and UV Issues
UV and deck material
While composite decking is built to withstand the elements, prolonged exposure to intense UV rays can, in rare cases, cause the surface polymers to degrade, leading to gradual fading. Most premium composite brands address this by incorporating UV inhibitors into the protective cap, which helps the boards retain their colour and finish for many years.
Fading often starts in areas receiving the most direct sunlight, such as edges and corners, causing slightly uneven tones over time. Simple practices like rotating outdoor rugs and furniture throughout the year can help distribute sun exposure and keep the deck’s appearance more consistent.
For new projects, it’s worth investing in capped composite boards with a high UV-resistance rating. Many manufacturers provide technical data on UV performance and testing under Australian conditions, making it easier to select a board specifically engineered to handle harsh sun without compromising its look.
Protective coating
Composite decking relies on a polymer cap for long-term protection rather than sealers or stains, but this cap can still wear over time. In high-traffic areas, the cap layer may thin slightly, exposing the core to moisture and UV. Regularly inspecting the boards for thinner sections or exposed fibres helps identify wear early.
Some deck owners choose to apply a composite-specific coating to restore the protective surface. These products bond with the cap, renewing water repellence and adding slip resistance. Always follow the board manufacturer’s recommendations when using these coatings.
For older decks showing significant cap wear, replacing affected boards may be more cost-effective than repeated recoating. Since matching new boards to faded sections can be challenging, replacing in stages can help blend old and new boards seamlessly.
Temperature extremes
Expansion and contraction cycles
Composite boards expand in heat and contract in cold. If boards are fastened too tightly or spaced incorrectly, this movement can cause buckling or warping. Following the recommended gap measurements in the installation guide ensures boards have room to move freely. Using breaker boards at intervals can also help absorb expansion and contraction, reducing stress on individual boards and maintaining a uniform deck surface. The buckling issue can often be resolved by releasing tension in the clips to allow freer movement.
Seasons in Australia vary from hot summers to cooler winters. Boards will progressively adjust length with temperature swings, so hidden clips, joist spacing, and strategically placed breaker boards must allow for this motion. Inspecting clips after the first few months of use confirms they are not impeding board movement.
Failure to account for expansion can also stress fasteners. Using the correct screw length, clip spacing, and appropriate placement of breaker boards reduces strain on the boards and prolongs the structural integrity of the deck.
Heat ‘’warping’’ in hot conditions
On very hot days, composite boards absorb heat and become slightly more pliable. If they are under load from heavy planters or furniture, they can bow or sag between joists. Using joist centres that meet or exceed manufacturer guidelines provides adequate support in extreme heat.
Dark-coloured boards absorb more heat than lighter tones, increasing the risk of heat-induced warping. If you live in a particularly hot region, choosing a lighter deck colour reduces thermal stress. Many composite ranges list a “cooler surface” colour option for sunny climates.
Regular removal of heavy objects and rotating furniture positions reduces pressure points on the deck. This allows boards to expand evenly without developing permanent bends or dips in the surface. All ‘’warping’’ or ‘’bowing’’ after installation is an installation issue that can be resolved by simply resetting the boards. It is not permanent, and with proper spacing, correct fastening, and routine care, your composite deck will maintain a smooth, safe, and visually appealing surface for years to come.
Installation mistakes
Incorrect spacing between joists
Deck joists must be spaced correctly to support the weight of the composite boards and any live load on the deck. Many composite products specify a 400mm to 450 mm joist spacing, but some hollow profiles require closer centres. Overly wide spacing leads to board sag under foot traffic and potential breakage.
Too narrow joist spacing is also problematic, preventing proper drainage and restricting board movement. By reviewing the joist spacing table on the installation guide, you ensure the correct centres for your chosen board profile.
Checking joist alignment before laying boards prevents end-of-board misalignment and reduces trimming waste. Straight and level joists help maintain a flush deck surface and minimise chances of boards slipping or moving out of place.
Inadequate fastening methods
Using the wrong fastener type or length may damage the board or void warranties. Composite decking often requires special hidden clips that grip the board edge without penetrating the board face. Mixing clip brands or using generic screws risks splitting or lifting.
Proper screw penetration under top-down installations also matters. Screws driven through the board face must be the correct length: long enough to engage the joist but short enough to avoid popping through the board underside. A depth-setting drill bit helps maintain consistent drive depth.
Failing to fasten starter boards properly can lead to gaps or uneven edges along the perimeter. Many products include starter clips designed for the first board edge. Securing this board correctly keeps all subsequent boards aligned and prevents end-gap movement.
Maintenance neglect
Infrequent cleaning routines
Dust, pollen, and dirt that build up on the deck surface act like abrasive particles underfoot. Regular sweeping or rinsing prevents surface wear and dulling of the polymer cap. In low-traffic areas, a monthly rinse with a garden hose is often sufficient.
For more stubborn grime, a composite deck cleaner can lift embedded dirt and restore slip resistance. Follow the manufacturer’s instructions carefully to ensure the correct dilution and avoid damage. For tougher stains, using a gurney or a high-pressure hose on a gentle setting can help remove built-up debris—just be cautious not to exceed the recommended pressure to avoid affecting the deck’s surface. After cleaning, always rinse thoroughly with plain water to restore the deck’s natural finish.
Failure to remove organic debris
Leaves, pine needles, and seed pods that settle in board gaps or under furniture can trap moisture against the board edges. Over time, this promotes mould and mildew growth. Removing organic matter weekly, especially during autumn, prevents staining and biological damage.
Cutting back overhanging branches also reduces debris fall onto the deck. Pruning trees or shrubs by a metre or two from the deck canopy improves airflow and sunlight exposure, keeping boards drier and healthier. Some deck owners install gutter guards or gap clips to keep larger debris out of board voids, making cleaning easier and lowering the risk of hidden mould build-up beneath the deck surface.
Key takeaways
With the right installation, routine cleaning, and attention to ventilation, drainage, and UV protection, your composite deck will not only outlast timber—it will stay beautiful, safe, and virtually maintenance-free for decades. Composite decking isn’t just an alternative to timber; it’s a long-term investment in your outdoor lifestyle.
