Blasting a patio with a zero-degree nozzle feels enormously satisfying. The dirt lifts instantly, the contrast is dramatic, and the results photograph beautifully.
It is also why the moss comes back faster every year.
High pressure does not just remove the green. It erodes the surface, opens up the pores, strips the jointing sand and leaves a rougher, more absorbent surface for spores to settle into. You are not cleaning the patio; you are sanding it, and each pass makes the next regrowth quicker.
Here is which surfaces take pressure, which do not, and what to do instead.
Nozzle angle is the control you are not using
Most damage comes from using the wrong nozzle rather than the wrong machine.
0 degrees, the pencil jet. A single concentrated point. It will cut timber, gouge mortar and etch stone. There is almost no legitimate cleaning use for it on a building. Keep it for a specific stubborn spot on hard concrete and nothing else.
15 degrees. Aggressive. Concrete, heavy machinery, hard standing.
25 degrees. The general-purpose choice for most hard surfaces.
40 degrees. Wide and gentle. Vehicles, render, timber, anything painted.
Soap or low-pressure nozzle. For applying chemicals.
Rotary or turbo nozzle. A zero-degree jet spun in a cone. Powerful and much faster on concrete, but far too aggressive for soft surfaces.
Distance matters as much as angle. Doubling the distance from the surface roughly quarters the force landing on it. Backing off a foot is often all that is needed.
Surface by surface
Block paving. Moderate pressure at 25 degrees, or better, a rotary surface cleaner. The real issue is the jointing sand, which pressure removes. Always re-sand after cleaning, or the blocks work loose, and weeds return within weeks.
Concrete and hard standing. Hard-wearing. Takes 15 or 25 degrees and a surface cleaner well. Watch for older concrete that has already started to spall.
Natural stone. Depends entirely on the stone. Sandstone and limestone are soft and erode easily, so stay wide and back off. Granite and slate take more. Test somewhere hidden first, always.
Brick and mortar. The brick is usually fine. The mortar is not, particularly on older lime-mortar buildings, where high pressure will remove joints and drive water into the wall. Use low pressure and chemistry.
Render, particularly K-rend and silicone renders. Do not pressure wash. It crazes and marks the finish, and once it is patchy it stays patchy. This is a soft washing job.
Timber decking and fencing. Very easily damaged. High pressure raises the grain and leaves permanent furrows. Use 40 degrees, keep well back, and work along the grain.
UPVC, cladding and conservatory roofs. Low pressure only. High pressure forces water past seals and into the building. Chemistry and a soft brush do it better.
Vehicles. 40 degrees at a sensible distance. Never a turbo nozzle. Keep away from seals, badges, trim and any existing paint chips.
Roofs. Generally not a pressure washing job at all. Water gets under tiles, and walking a roof is a fall risk. Soft wash from a safe position.
Soft washing: pressure is not always the answer
Soft washing applies a cleaning solution at low pressure, lets it work, then rinses gently. The chemistry kills the organic growth rather than blasting it off.
It is slower on the day, and it lasts far longer, because it kills the spores rather than removing the visible top layer. On render, delicate stone, timber and roofs, it is the correct method rather than a compromise.
A pressure washer is still the tool. You are just using it at a fraction of its capability, with a chemical injector and a wide nozzle, and letting dwell time do the work.
The general rule: if the surface is soft, porous, painted, coated or sealed, reach for chemistry. If it is hard, dense and unfinished, pressure is fine.
The accessory that changes the job
For any flat area, a rotary surface cleaner is the single biggest upgrade you can make.
It encloses two spinning jets under a shroud. That does three things: it cleans several times faster than a lance, it applies pressure evenly so you get no tiger stripes, and it contains the spray so you are not redistributing dirt across the windows.
Anyone cleaning patios, driveways or yards regularly and still using a lance is working perhaps three times harder than necessary and getting a less even result.
Before you start
Five minutes that prevents most callbacks.
- Test in a hidden corner and wait for it to dry before judging
- Check the mortar and pointing, and stay off anything loose or perished
- Wet the surface first so dirt lifts rather than driving in
- Work top to bottom on walls, and keep a wet edge
- Protect planting by wetting it before and rinsing it after, particularly if you are using chemicals
- Think about where the water goes. On a commercial job, run-off carrying chemicals or oil should not enter a surface water drain
Frequently asked questions
Can you damage a patio with a pressure washer?
Yes, easily. High pressure erodes the surface, opens up the pores and strips jointing sand, which makes moss and weeds return faster each time. Use a 25 degree nozzle or a rotary surface cleaner rather than a zero degree jet, keep your distance, and re-sand block paving afterwards.
Should you pressure wash render?
No. Modern renders, including K-rend and silicone finishes, craze and mark under pressure, and the damage is permanent and patchy. Render should be soft washed, applying a cleaning solution at low pressure, allowing dwell time, then rinsing gently.
What is soft washing?
Soft washing applies a cleaning solution at low pressure and lets the chemistry kill organic growth, then rinses gently rather than blasting. It takes longer on the day but lasts significantly longer, because it kills spores rather than removing the visible surface layer. It is the correct method for render, delicate stone, timber and roofs.
What nozzle should I use for a patio?
A 25-degree nozzle for general work, or better, a rotary surface cleaner, which cleans faster and far more evenly with no striping. Avoid the zero-degree pencil jet entirely on paving, as it gouges the surface and removes jointing sand.
Can you pressure wash decking?
With care. Timber is soft and high pressure raises the grain and leaves permanent furrows. Use a 40 degree nozzle, keep well back, work along the grain rather than across it, and test on a hidden board first. Lower pressure with a suitable cleaner gives a better result.
The bottom line
The machine is rarely the problem. The nozzle, the distance and the choice between pressure and chemistry are where jobs are won or ruined.
Test first, go wider than feels necessary, and use a surface cleaner on anything flat.
Kränzle UK stocks rotary surface cleaners, the full nozzle range and chemical injectors alongside every machine. Tell us what surfaces you clean, and we will put the right kit together rather than selling you the most powerful thing on the shelf.