Learn about the most common decking problems and how to fix them. Our guide can help you prevent and fix issues such as rot, warping, loose railings and more.
Warped or Cracked Deck Boards
Warped or cracked deck boards are some of the most common issues homeowners face due to damp weather and constant wet-dry cycles. Softwood decking in particular absorbs moisture, swells, then shrinks in the sun, which causes the boards to twist and create gaps.
Composite decking can resist these issues better, but they aren’t immune to heat-related warping or cracking if the boards are poorly installed without expansion gaps. Poor ventilation under the deck, tight board spacing, and loose nails can also make these issues worse.
If the deck boards bow between the joists, the sub-structure may be undersized or damp, and if the warping spans across the deck's width, the gaps might be clogged with water trapped underneath. To fix a minor cupping or a gentle bow, you should remove the fixings, flip the board, and refit the decking with corrosion-resistant screws (not nails) into the joists. You should use two screws per bearing and pre-drill the screws near the edges.
However, if there are persistent twists or splits, it's best to replace the boards altogether. In this scenario, you should ideally cut the board free, lift it with a pry bar, fit a new pressure-treated board of the same thickness, and leave 5-6 mm gaps for drainage. Additionally, you should check the joists for any softness or rot, since that will need to be addressed before the new boards are fitted.
Rotting or Decayed Wood
Rotting or decayed decking is another widespread problem that homeowners face due to the UK's damp climate and frequent rainfall. Even when it's pressure-treated, timber can still be highly susceptible to fungal decay if it stays damp for long periods of time and doesn't have adequate airflow.
Decking that sits too close to the ground, is shaded by trees, or lacks proper drainage, is also vulnerable to rot and decay. Over time, moisture can penetrate the wood fibres and break them down, which causes soft spots, crumbling edges, and in severe cases, complete structural failures.
Homeowners should check for boards that feel spongy, have dark patches, or flake apart. Algae and moss growth are also signs that there's persistent damp, which can cause the decking and joists to rot. The best way to fix decaying deck boards is to replace them completely.
The damaged boards should be carefully lifted with a pry bar or a circular saw, then swapped out for new pressure-treated timber of the same dimensions. It’s important to check the joists beneath the deck boards for any hidden decay, and if rot is present, the joists need to be replaced too.
In cases where the decay is minor, homeowners can apply a wood hardener or an exterior epoxy filler to stabilise the soft areas.
However, this is more of a short-term fix, rather than a permanent solution. Regular sanding and re-sealing with a high-quality decking oil or preservative can also help slow down any rot or decay.
Wobbly or Unstable Railings
Wobbly or unstable deck railings are a common issue that's usually caused by a mix of bad weather, timber movement, undersized fixings and hidden rot. Repeated wet-dry cycles can make the wood shrink and swell, which can loosen the screws, accelerate the rate of corrosion and warp the decking posts.
To identify this issue, you should give the top rail a firm shake. If the whole rail moves, there's an issue with the posts and their connection to the frame. However, if only a small section of the decking rattles, you should check for any loose brackets, cracked rails, or spindles. The post bases should also be checked for softness, dark stains, or crumbling end grains, as well as rusty screws or nails.
To fix this issue, you should replace the nails and screws with exterior-grade structural screws or coach bolts with washers. All the connections, including rail-to-post brackets, should be tightened, and any corroded hardware should be replaced with galvanised or stainless steel.
Additionally, the posts shouldn't rely on just the screws and rim joists alone. Instead, you can add solid blocking between the joists behind each post, and then through-bolt the post, rim, and blocking together to create a more stable base.
Mould, Mildew and Algae Growth
Cold, damp weather, shaded gardens and frequent rainfall create the perfect conditions for mould, mildew and algae to grow. Besides looking unsightly, mould and algae can make your decking dangerously slippery and increase the rate of decay in softwood.
To check for these issues, you should inspect any boards that have clear gaps of around 5-6 mm, and you should check that water can run off the deck and away from your house. If you find that any of the gaps are clogged with debris, it's likely that mould and algae will start to grow if the gaps aren't drained.
For cleaning, it's best to start by sweeping away leaves, soil and loose plant growth with a brush. This allows you to lift up the bulk of the debris so that cleaners can reach the surface evenly and reduce the risk of smearing algae into the wood. The deck should then be washed with an appropriate cleaner.
Oxygen-based deck cleaners (sodium percarbonate) work well because they lift organic staining without bleaching the wood. You should then keep the surface wet for at least 10-15 minutes, scrub the cleaner into the grain and then rinse the deck thoroughly to remove any residue.
For preventing mould, mildew and algae, you should ensure that there’s at least 150 mm of clear space beneath the deck so that damp air can escape. If you have solid skirting, you should add ventilation gaps or remove sections of the decking to prevent moisture from lingering.
Overhanging branches should be pruned so that sunlight can be let in, and gutter guards or splash deflectors should be fitted where the roof runoff hits the deck so that water doesn’t stay trapped underneath.
Additionally, the 5-6 mm gaps between the boards should be kept clear using a deck-gap scraper or a thin putty knife to help stop water from pooling around the joists and fixings.
At Welcroft Lee Logistics, we can repair warped boards, loose railings, sagging decking, and treat rotted decking. We constantly use durable and weatherproof materials to help keep your decking strong and beautiful all year round. From minor fixes to full replacements, we can keep your deck safe and durable. Find out more about decking repair in Eastbourne, Brighton & Hastings.
