A green film on patio slabs can become much more noticeable after wet weather. The surface stays damp, especially in shaded areas, and algae or moss can build up over time. Patios beside fences, walls and overhanging plants often take longer to dry than open areas.
The right way to clean it depends on the paving material and its condition. Before reaching for a pressure washer, it helps to understand why the green patches keep returning.
Check where moisture stays longest
Look at the patio at different times of day. Are the green areas always in shade? Does water collect near a step, wall or garden border? Are leaves sitting in corners or between pots?
These observations can point to places that remain damp. Removing loose leaves and keeping drainage points clear may help reduce the build-up between deeper cleans.
Clean carefully around joints and edges
Green growth is often most visible along joints, steps and edges where dirt collects. Regular sweeping can remove loose material before it sits on the surface. If the area needs a deeper clean, the method should suit the paving.
Concrete, natural stone, older slabs and other patio surfaces do not all respond the same way to pressure or cleaning products. Excessive pressure can affect worn surfaces or joints, so inspect the condition first.
Why does the green colour come back?
Cleaning removes the visible build-up, but the patio may still have the same shade and damp conditions afterwards. That means some areas will need more regular maintenance than others. Keeping nearby debris off the slabs and watching for standing water can help you spot the problem early.
If the green film returns quickly or a large area is affected, take a few photos in daylight. Include close-ups of the slabs and a wider view showing drainage and access. Those details help a cleaner assess the surface and suggest a suitable approach.
Getting help with patio cleaning
Crown Clean London provides patio cleaning in London, including exterior cleaning in Wembley. We check the surface type, condition and level of build-up before choosing a cleaning method.
Want a quote? Send us photos and your postcode, along with a note about the green or slippery areas you want cleaned.