Hard Landscaping · 13 October 2026 · 4 min read

Jet Washing a Patio Safely Without Damaging It

Few jobs are as satisfying as jet washing a green, slippery patio and watching the clean stone appear. It is also a job where people frequently do damage: stripping the surface of soft stone, blasting out the joints between slabs, or leaving stripes. Done properly, it is straightforward.

Is autumn a good time?

Algae and moss grow fastest on damp, shady paving in autumn, and slippery paving is a real fall hazard when leaves are down. So a clean now makes sense. But avoid jet washing if frost is forecast. Wet paving that freezes becomes an ice rink, and water in the surface of some stone can freeze and cause damage. Choose a dry, mild day, and give the surface time to dry afterwards. If it has been wet for days, patience helps.

Know your surface

Different paving reacts differently.

Indian sandstone and other natural sandstone: softer than people expect. High pressure and rotating nozzles can etch the surface, leaving visible lines and removing the finish. Use lower pressure, a wide fan nozzle and keep your distance.
Limestone: soft and can be marked by acid-based cleaners.
Concrete slabs and block paving: tougher, but the surface layer can still wear away and joints can be blasted out.
Porcelain: very hard and generally easy to clean, but joints still need care.
Tarmac and resin-bound surfaces: high pressure can damage them. Resin-bound surfaces in particular need low pressure, and it is wise to follow the installer's guidance.

If you are unsure, test a small, discreet area first.

Choosing equipment

Domestic pressure washers vary a lot in power. More power is not automatically better. What matters is being able to control it. Aim for a machine and nozzle that let you reduce the pressure for delicate surfaces. A flat fan nozzle (rather than a pinpoint jet) spreads the force. Surface cleaner attachments, which have a spinning arm in a hood, give a more even result and reduce striping, and they cut splashing.

Rotary "turbo" nozzles are fast but aggressive, and are best avoided on soft stone or near joints.

Before you start

Sweep the patio and remove furniture, pots and anything loose.
Check the weather, and avoid hot sun, which makes treatments dry too quickly.
Protect doors, windows, air bricks and anything you do not want water or debris going into. Do not point the jet at door frames or the base of walls, as high-pressure water can force its way past seals and into cavity walls or under the damp proof course.
Wear eye protection, waterproof boots with grip and clothing you do not mind getting dirty. The jet can throw grit, so keep other people and pets well away.
Check hoses and connections for leaks, and use an RCD if the machine is mains-powered.

Technique

Start with the nozzle a good distance from the surface, say 30 to 50 cm, and move closer only if needed.
Hold the lance at an angle, around 30 degrees to the surface, rather than straight down, and sweep in smooth, overlapping strokes.
Work in sections in straight lines, keeping the speed even, to avoid zebra stripes.
Work from the house outwards and slightly downhill so dirty water runs away from where you have cleaned.
Do not linger on one spot, particularly on softer stone.
Keep the jet away from the joints as far as possible. Blasting the joints removes the sand or mortar that holds the paving together and lets weeds in.

Dealing with stubborn algae and moss

Ordinary water pressure removes most surface growth, but black or green staining can come back quickly. A patio cleaner or an algae treatment designed for paving can help. Check that it suits your surface and follow the directions exactly. Be careful with where run-off goes: do not let chemical cleaners run into streams or surface water drains, which go straight to the rivers in most areas. Many people use as little chemical as possible and just clean again in a year or two.

Re-sand or re-point the joints

After cleaning, check the joints. On block paving, brush in kiln-dried jointing sand or a polymeric sand, following the instructions, until the gaps are full, then sweep off the excess. On slabs with pointed joints, repair any missing mortar. Open joints let weeds, ants and water in. If you want to cut down on weeds, see our guide to controlling weeds in autumn.

Sealing

Some people seal patios after cleaning to slow re-growth and protect against stains. Sealers need a completely dry surface and suitable weather, and a poor application can leave a patchy, sticky or shiny finish. Test a small area, and choose a product made for your type of stone. Not every patio needs sealing.

Neighbours and water use

Jet washing is noisy, and the spray can drift. Consider your neighbours. Keep water use sensible, as some water companies restrict hosepipe use during drought, so check whether any restrictions apply.

Common mistakes

Using a turbo nozzle too close to soft stone.
Blasting out joints, then not refilling them.
Washing in freezing conditions.
Pointing the jet at walls, windows and doors.
Leaving it half done and uneven.

Looking after the machine

Drain it before winter, as covered in our post on preparing tools for winter. Also see the notes on clearing leaves from paving regularly, which stops staining and slipperiness in the first place.