Patio Cleaning: How to Clean Patio Slabs Safely

The right approach depends on what the patio is made of, so it is worth working that out before reaching for a jet washer.

Green algae and moss are the usual culprits on a slippery patio, especially in shady corners. They respond well to cleaning and treatment, and the patio will usually look very different afterwards.

Black spot is the stubborn one. These small dark marks are lichen rooted into the surface of the stone, often on sandstone. Pressure alone tends not to remove them and turning the pressure up is how slabs get damaged. They usually need a suitable treatment and time to work, and even then it is fair to expect improvement rather than perfection.

A jet washer at full power held close to a slab can etch the surface of soft stone, leaving lines and a rough, patchy finish that then holds dirt faster than before. It can also blast the jointing material out from between slabs. Once joints are open, weeds take hold and slabs can start to rock.

Better results come from a lower pressure, a wider nozzle or a rotary surface cleaner, and keeping the lance at a shallow angle so you lift the grime rather than drilling into the stone. Patience gets a better finish than force.

Every patio is different, but this order works for most.

After cleaning, look closely at the joints. If they are loose sand that has washed out, they will need refilling with suitable jointing sand once the patio is dry. Patios with mortar or resin joints should be checked for cracks and gaps. Skipping this step is why some patios look great for a fortnight and then sprout weeds everywhere.

Some patios are better left to a gentler clean. Very old or crumbling sandstone, slabs with failing joints, freshly laid patios and surfaces in freezing weather are all better treated with care. If water will run towards an air brick, a door threshold or into a neighbour's garden, plan the direction of the wash before you start.

The price of patio cleaning depends on the area, how heavily soiled it is, the slab type, whether treatment for algae or black spot is needed, whether joints need refilling and how easy it is to reach with hoses and power. Steps, walls and raised beds add time. Our pressure washing service assesses the surface first and explains what can realistically be improved before any work starts.

Patio cleaning prices are shaped by the size of the patio, the type of stone, how much moss, algae and black spot has built up, whether furniture and pots need moving, how easy it is to get equipment into the garden and whether the joints need refilling afterwards. A small porcelain patio with light algae is a quicker job than a large sandstone terrace with years of growth.

The same factors drive pressure washing cost for drives and paths. Photos and a rough size let a company confirm a price for the agreed job rather than an estimate that changes on the day.

A small patio with light growth is often fine to tackle yourself with a stiff brush and a suitable cleaner. A large area, delicate stone or heavy black spot is where a professional clean is usually worth it, because too much pressure on the wrong stone can etch the surface or wash out joints.