Experts in Concrete Patio installation

Why Your Patio Is Discolouring – And What You Can Do About It

Has your patio lost its even tone or developed dark blotches, patches, or strange colour streaks? Patio discolouration is a common issue in UK gardens, and it can affect even brand-new concrete installations.

In this guide, we explain the typical causes of discolouration, from weather and wear to sealant issues, and show you the best ways to clean, restore, and protect your patio so it looks its best year-round.

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What Causes Patio Discolouration?

Patio discolouration can be caused by surface contamination, moisture issues, or even problems with the original installation. Understanding where the problem comes from helps you treat it more effectively, and prevent it coming back.

Efflorescence (Salt Deposits)

White or light-grey powdery patches on the surface are often caused by efflorescence, salts migrating to the surface as moisture evaporates from within the slab. It's harmless but unsightly, and more common in new patios or during wet winters. It usually fades naturally, but persistent cases may require a specialised cleaner.

Algae, Moss or Mould Growth

Green, black or dark grey staining is usually caused by organic growth on damp surfaces. Algae and mould thrive in shaded, wet areas, particularly in the UK’s mild, wet climate. Without regular cleaning and sealing, these stains can become ingrained in the surface and difficult to remove.

Uneven Curing or Sealing

If a patio wasn't cured or sealed evenly during installation, it may develop uneven patches of colour. Overuse of water, inconsistent finishing, or poor sealing techniques can all create blotchy areas that don’t match the surrounding concrete. These can often be improved with a surface scrub and a colour-enhancing sealer.

Water Ponding or Drainage Issues

Standing water leads to dark or stained areas where moisture is retained longer. These spots not only look different, but they may also indicate underlying issues with drainage or patio slope. Left untreated, they can become hotspots for moss or frost damage too.

Stains from Furniture, BBQs or Fertilisers

Rusty legs, plant food, or grease from a barbecue can all leave long-term marks on unsealed concrete. These stains are often darker than the surrounding area and tend to soak into porous surfaces over time. The longer they sit, the harder they are to remove, so early action is key.

How to Clean and Restore Patio Colour

Identify and Treat the Stain

Use a concrete-safe patio cleaner matched to the type of stain (e.g. algae, rust, grease).
Scrub gently with a stiff brush or pressure washer, focusing on discoloured patches.
Avoid bleach unless the area is well-rinsed, as it may affect nearby plants or soil.

Even Out Colour with a Restorative Sealer

If discolouration remains after cleaning, consider applying a colour-enhancing or tinted sealer.
This helps bring consistency back to faded or patchy surfaces while protecting against further staining.
Choose a breathable, non-slip sealer designed for outdoor concrete patios.

Prevent Future Discolouration

Seal your patio every 2–3 years and avoid placing rusty or greasy objects directly on the surface.
Keep the patio clear of leaves, plant pots, and fertilisers that may leach into the concrete.
Improve drainage and light exposure where possible to discourage moisture-loving stains.

Frequently Asked Questions

This is likely efflorescence, a natural salt that rises to the surface as moisture evaporates. It's not harmful and usually fades over time. If needed, a specialist cleaner can help speed up removal.

Algae and moss can leave dark stains if allowed to grow unchecked. However, with proper cleaning and surface sealing, you can usually remove them and restore the patio's colour without permanent damage.

Pressure washing is effective for surface stains but may not resolve deeper discolouration caused by curing issues or embedded stains. For best results, combine it with appropriate cleaners and sealants.

Keep the area well-drained and free of shade-loving moss. Regular brushing, sealing, and good airflow will help prevent green algae and mould from building up on the surface.

We cover discolouration caused by workmanship issues such as uneven sealing or curing faults. Natural weathering and stains from furniture or fertiliser are not covered but we can help restore the surface as part of aftercare.