How to Clean a Patio

Patio slabs aren't all the same, and the right method depends on the material. Indian sandstone is very common in UK gardens; it's natural stone, fairly soft and porous, and can be marked by strong acids and very high pressure. Porcelain paving is hard, non-porous and easy to clean. Concrete slabs are tough but can lose their surface texture under a close pressure washer jet. Slate and limestone are natural stones that react badly to acidic cleaners.

If you're not sure what you have, assume it's natural stone and start gently.

Move furniture, pots and barbecues off the patio. Sweep thoroughly with a stiff broom to remove leaves, soil and loose debris, then pull or scrape out weeds and moss from the joints with a patio knife or weeding tool. Doing this first means the washing stage actually reaches the surface of the slabs.

Check where water will run. Washing water carrying dirt and cleaning products shouldn't go into roadside drains, which often lead straight to watercourses. Let it soak into the garden or drain to a gully connected to the foul sewer.

For a light clean, a bucket of warm water with washing-up liquid and a stiff deck scrubber is enough. Scrub in sections, then rinse with a hose. It's slow on a large patio but gentle on any material.

For green algae and lichen, use a patio cleaner designed to kill algae – many are 'apply and leave' products that work over days or weeks with the help of rain. Choose one labelled suitable for your paving, apply it on a dry day as directed and keep children and pets off until it has dried. Avoid bleach, which harms plants and wildlife and can discolour stone.

A pressure washer makes the job far quicker, but it's also the main way patios are damaged. Use a wide fan nozzle rather than a pinpoint jet, keep the lance moving and hold it at an angle about 20–30cm from the surface. Work in the direction of the joints rather than across them, to avoid blasting out the jointing.

A patio cleaner attachment – a rotating disc with a hood – gives a more even result with less splashback and is kinder to joints. Start in a less visible corner to check the stone isn't marking. Wear eye protection and closed shoes, and keep children and pets well away.

Pressure washing almost always removes some jointing material. Once the patio is completely dry, check the gaps. Sand-filled joints can be topped up with kiln-dried sand brushed in; mortar joints with cracks or gaps may need repointing; resin jointing compounds are another option that resist weeds better.

Sealing is optional. A breathable stone or paving sealer can make sandstone and concrete easier to clean and reduce staining, but it can change the appearance (some add a slight sheen or darken the colour) and needs reapplying every few years. Porcelain doesn't need sealing.

Treat specific marks before or after the general clean:

Exterior cleaning companies clean patios, driveways and paths using rotary surface cleaners, hot water and biocide treatments, and many re-sand the joints afterwards. It's often priced per square metre or as a fixed price for the area, with re-sanding and sealing as extras. Some window cleaners and general cleaning firms offer it alongside window cleaning and gutter clearing.

Ask what method they'll use on your type of paving, whether jointing is included, how they'll deal with run-off and whether they're insured for damage to property. Our guide to driveway and block paving cleaning covers similar questions for driveways.

Sweep the patio regularly, especially in autumn when wet leaves stain and encourage algae. Keep overhanging plants trimmed back to let light and air reach the slabs. A patio treatment applied once or twice a year slows algae regrowth, and a quick scrub of any green patches in spring stops them spreading.