Jet Wash Nozzles and Pressure Washer PSI Explained
Jet wash nozzles decide how hard the water hits a surface. Pick the wrong one and you can etch concrete, wash the sand out of block paving or splinter timber decking. Pick the right one and the same machine lifts moss, algae and grime without leaving a mark. This guide explains what each nozzle does, what pressure washer PSI means, and how to match both to driveways, patios and decking.
Most domestic and professional pressure washers use the same colour coded nozzle system, so once you know the colours you can read almost any machine.
Jet Wash Nozzles Explained by Colour
Nozzles are rated by the angle of the spray fan. A narrow angle puts the water on a small area and hits harder. A wide angle spreads the same water over more surface and hits softer.
- Red, 0 degrees: a pencil thin jet that cuts through stubborn spots but can gouge paving, wood and render in seconds. Most jobs never need it.
- Yellow, 15 degrees: a narrow fan for tough stains on hard concrete. Keep it moving and keep your distance.
- Green, 25 degrees: the general purpose nozzle for driveways, block paving and most patios.
- White, 40 degrees: a wide, gentle fan for decking, fences, soft stone and painted surfaces.
- Black, 65 degrees or soap nozzle: low pressure for applying detergent and rinsing.
Turbo or rotary nozzles
A turbo nozzle spins a 0 degree jet in a circle, so it combines the power of the red nozzle with a wider cleaning path. It works well on concrete and tarmac with ingrained dirt, but it is too aggressive for sandstone, older block paving and timber.
Surface cleaners
A surface cleaner is a round hood with spinning jets underneath. It holds the nozzles at a fixed height, which stops the stripes, often called tiger marks, that appear when a patio is cleaned with a hand lance.
What Pressure Washer PSI Means
PSI stands for pounds per square inch and measures the force of the water leaving the nozzle. Most domestic machines sold in the UK produce somewhere around 1,500 to 2,200 PSI. Professional machines usually run at 2,500 to 4,000 PSI and are paired with nozzles and surface cleaners that control how that force reaches the ground.
Higher PSI cleans faster, but it also raises the risk of damage. The safest approach is to start with a lower setting and move up only if the surface needs it.
Flow rate matters as much as PSI
Flow rate, measured in litres per minute, tells you how much water the machine moves. Pressure loosens the dirt, while flow carries it away. A machine with high PSI and low flow can blast a surface yet leave a film of dirt behind, which is why commercial machines are built for higher flow as well as higher pressure.
What PSI to Clean a Driveway, Patio or Decking
Use these figures as a starting point and always test a small hidden area first.
- Concrete driveways: around 2,500 to 3,000 PSI with a 15 or 25 degree nozzle, or a turbo nozzle for heavy staining.
- Tarmac driveways: around 1,500 to 2,000 PSI with a 25 or 40 degree nozzle. Tarmac softens in warm weather, so avoid hot days.
- Block paving: around 2,000 to 2,500 PSI with a 25 degree nozzle or a surface cleaner, spraying at a low angle so the sand stays in the joints.
- Sandstone and natural stone patios: around 1,200 to 1,500 PSI with a 40 degree nozzle, as soft stone marks easily.
- Porcelain patios: around 1,500 to 2,000 PSI with a 25 or 40 degree nozzle.
- Timber decking: around 500 to 1,200 PSI with a 40 degree nozzle, working along the grain.
For the full step by step method on paving, read our guide on how to clean block paving.
Domestic Machines Compared With Professional Equipment
A domestic pressure washer is built for occasional use on small areas. Professional equipment differs in 3 ways that matter on bigger jobs.
- Pressure and flow: commercial units deliver more of both, so a large driveway takes a fraction of the time.
- Hot water: some professional machines heat the water, which shifts oil, chewing gum and grease that cold water leaves behind.
- Control: surface cleaners, adjustable lances and pressure regulators give an even finish across a large area.
For a small patio, a domestic machine with the right nozzle is usually enough. For large driveways, oil staining or delicate stone, our jet washing services take the guesswork out of choosing settings.
Common Nozzle and PSI Mistakes
- Using the red nozzle to save time, which leaves lines cut into paving.
- Holding the lance too close. Around 30cm away is a sensible starting distance.
- Spraying straight down into block paving joints, which washes out the sand.
- Using high pressure on render or painted walls, which can lift the finish.
- Skipping a test patch on old or natural stone.
Jet Wash Nozzles and PSI FAQs
What do the colours on pressure washer nozzles mean?
The colours show the spray angle. Red is 0 degrees, yellow is 15, green is 25, white is 40 and black is the low pressure soap nozzle. The narrower the angle, the harder the water hits, so red and yellow suit only hard, stubborn surfaces and white suits delicate ones.
Which pressure washer nozzle should I use on a patio?
Start with the green 25 degree nozzle for concrete, porcelain or block paving patios, and switch to the white 40 degree nozzle for sandstone or other soft natural stone. Keep the lance moving about 30cm from the surface, and test a hidden corner before you clean the whole area.
What PSI do I need to clean a driveway?
Most concrete driveways clean well at around 2,500 to 3,000 PSI, while tarmac needs a gentler 1,500 to 2,000 PSI so the surface does not break up. Block paving sits in between at around 2,000 to 2,500 PSI. Pair the pressure with the right nozzle, as a narrow jet can still mark paving.
Can jet washing damage block paving?
Yes, if the pressure is too high or the spray points straight into the joints. That washes out the jointing sand, loosens blocks and lets weeds return quickly. Use a 25 degree nozzle or a surface cleaner, spray at a low angle, and re sand the joints with kiln dried sand once the surface is dry.
Is a higher PSI pressure washer always better?
No. Higher PSI cleans faster on hard concrete, but it also increases the risk of etching stone, stripping paint and splintering wood. Flow rate matters just as much, because water volume carries the dirt away. A balanced machine with the right nozzle usually gives a better finish than raw pressure alone.
