How Does Pressure Cleaning Work? Complete Guide

Pressure cleaning works by using a pump to force water through a small nozzle at high pressure. The fast-moving water breaks the grip between dirt and a hard surface, and the flow of water then carries the loosened grime away. Two numbers decide how well it cleans: pressure (measured in PSI or bar) and flow (measured in litres per minute). The nozzle, the distance you hold it from the surface, detergent and water temperature fine-tune the result. Get that balance wrong and the same machine that lifts years of grime can etch concrete, splinter timber or strip paint. This guide explains each part of the process, the pressure that suits common Australian surfaces, the safety and water rules that apply in Sydney, and how to tell whether a job is a weekend DIY or one for a professional crew.

What Is Pressure Cleaning

Pressure cleaning services is cleaning hard surfaces with water delivered at far higher pressure than a garden hose can produce. In Australia it is also called pressure washing, high-pressure cleaning or pressure hosing. “Power washing” usually means the same thing, although some people use it only for machines that heat the water. A garden hose relies on mains pressure and volume. That rinses away dust, but it can’t break the bond of oil, algae, tyre marks or ground-in grime. A pressure cleaner uses a pump to multiply the pressure many times over and squeezes the water into a narrow, fast jet that can. It is used on concrete driveways and paths, pavers, brick, stone, pool surrounds, car parks, bin rooms, loading docks and building exteriors. Softer, painted or older surfaces usually need lower pressure or soft washing instead, which is covered further down.

Read more about pressure cleaning complete guide

Inside a pressure cleaner: how the machine works

Every pressure cleaner, from a small electric unit to a trailer-mounted commercial rig, moves water through the same chain of parts:

1. Water supply: A tap or tank feeds water into the machine through an inlet filter that keeps grit out of the pump.
2. Motor or engine: An electric motor (most home units) or a petrol or diesel engine (most commercial units) drives the pump.
3. High-pressure pump: Pistons (plungers) inside the pump squeeze the water and push it out at high pressure. The pump sets the machine’s maximum pressure and flow.
4. Unloader valve: When you release the trigger, this valve sends the water around a bypass loop so pressure doesn’t build up dangerously in the hose.
5. High-pressure hose: Carries the water to the gun. It must be rated for at least the machine’s maximum pressure.
6. Trigger gun and lance: Control the spray and keep your hands and feet well back from the jet.
7. The small opening at the tip turns pressure into a fast jet. Its size and spray angle decide how concentrated that jet is.

Some machines add a burner to heat the water, a chemical injector to draw detergent into the line at low pressure, or a surface cleaner (a spinning bar under a round hood) for fast, even cleaning of flat concrete.

Pressure, flow and cleaning power

Pressure is measured in PSI (pounds per square inch) or bar. Machines sold in Australia usually show both on the rating plate; 1 bar is about 14.5 PSI. Flow is measured in litres per minute (L/min).

The two do different jobs. Pressure cuts into the dirt and lifts it. Flow carries it away. A machine with high pressure but low flow cleans slowly and can still gouge a surface; a machine with high flow but low pressure pushes loose debris but won’t break tough bonds. That is why professionals compare machines on both numbers, not pressure alone.

Machine type	Typical pressure	Typical flow	Best suited to
Light-duty electric	1,300–2,000 PSI (90–140 bar)	5–8 L/min	Cars, outdoor furniture, small patios and paths
Heavy-duty petrol	2,000–3,500 PSI (140–240 bar)	About 8–12 L/min	Driveways, large paved areas, no power point nearby
Commercial / industrial	3,000 PSI (205 bar) and above	15 L/min and above	Car parks, loading docks, plant and large sites
Hot-water unit	Similar to petrol or commercial	Similar	Grease, oil and food fats (kitchens, bin rooms, workshops)
Soft wash system	Under 500 PSI (35 bar), often much lower	Varies	Roofs, render, painted walls and cladding

These are typical ranges, not rules. Always check your machine’s rating plate and the surface manufacturer’s guidance.

Nozzles: how spray angle changes the result

The nozzle decides how concentrated the water is when it hits the surface. A narrow angle puts all the force on a small spot; a wide angle spreads it out. Most quick-connect nozzles are colour-coded:

Colour	Angle	Use it for	Avoid on
Red	0° (pin jet)	Spot-cutting stubborn deposits on bare steel or hard concrete only	Almost every building surface — it can cut grooves and injure skin
Yellow	15°	Heavy cleaning of hard concrete and steel	Paint, timber, render, pavers
Green	25°	General cleaning of concrete, pavers and brick	Soft or old surfaces (test first)
White	40°	Timber, cladding, vehicles and rinsing	Window seals, vents, loose mortar and flaking paint at close range; it can still force water behind them
Black	65° / low pressure	Applying detergent	Hot surfaces in direct sun, where detergent dries and streaks; it is too weak for removing grime on its own

Distance matters as much as the nozzle. Moving the tip further away reduces the impact quickly, so start about 50–60 cm from the surface and move closer only if the surface stays undamaged. On large flat areas, a surface cleaner attachment gives an even, stripe-free finish that a hand lance struggles to match.

For a deeper guide to tips, lances and turbo nozzles, see choosing nozzles and lances.

Detergents and hot water

Water pressure removes what is sitting on a surface. Detergents and heat deal with what is stuck to it.

• Detergents and surfactants lower the surface tension of water so it can get under oily films and organic growth.
• Degreasers break down engine oil and grease on driveways, car parks and loading bays.
• Mould and algae treatments (biocides) kill organic growth so it doesn’t simply grow back. They work through dwell time, not pressure.
• Hot water (commonly 60–90°C on commercial units) softens grease and fats and speeds up the cleaning chemistry. It is the standard for commercial kitchens, bin rooms and workshops.

Apply chemicals at low pressure, leave them for the dwell time on the label without letting them dry, then rinse. Choose biodegradable products where possible, because every chemical you use ends up in the wash water you have to manage (see the NSW rules below).

For a full comparison, read hot water vs cold water pressure cleaning.

Pressure washing vs soft washing

Soft washing is the low-pressure alternative. It uses well under 500 PSI (35 bar) and relies on cleaning solutions to kill and loosen mould, algae and lichen, which are then gently rinsed off.

	Pressure washing	Soft washing
How it cleans	Force of the water jet	Chemistry and dwell time, then a gentle rinse
Pressure	Roughly 1,300–3,500 PSI (90–240 bar)	Under 500 PSI (35 bar)
Best for	Concrete, pavers, hard brick, stone, metal	Roofs, render, painted walls, cladding, older brick
Main risk	Etching, gouging, forcing water into joints	Chemical overspray onto plants and runoff

Roofs deserve a special mention: high pressure can force water under tiles, strip protective coatings and void roof warranties, so most roof cleaning is done by soft washing from proper height-safety access. Read more in soft washing vs pressure washing vs power washing.

Safe pressure for common surfaces

Here’s the table with the empty nozzle cell filled in:

Surface	Starting pressure	Nozzle	Watch out for
Concrete driveways and paths	2,000–2,800 PSI (140–195 bar)	25° or surface cleaner	Exposed aggregate, swirl marks, pin-jet lines
Concrete or clay pavers	From about 1,500 PSI (105 bar)	25° or surface cleaner	Blasting out joint sand — re-sand afterwards
Timber decks and fences	500–1,200 PSI (35–85 bar)	40° or wider	Furred fibres, splinters, stripped stain — work with the grain
Brick and stone	800–1,500 PSI (55–105 bar)	40°, or 25° on hard brick	Eroded mortar joints; heritage brick needs specialist methods
Render and painted walls	Soft wash preferred	40° or wider if rinsing	Lifted paint, gouged render, water behind cladding
Roof tiles and metal roofs	Soft wash	Black 65° or a soft-wash nozzle; rinse downward, never upward	Water under tiles, stripped coatings, falls from height
Cars	1,300–1,900 PSI (90–130 bar)	40°, 30–60 cm from paint	Damaged trim, decals and clear coat

Use this as a starting point, not a target. Begin at the low end, test in a hidden spot, and only increase pressure if the surface shows no damage. Age, coatings and condition matter more than the number.

For stain-by-stain and surface-by-surface detail, see pressure cleaning methods by surface and stain.

The pressure cleaning process, step by step

Whether it is a small patio or a strata car park, a good pressure clean follows the same order:

1. Look for cracks, loose render, peeling paint, rotten timber and open joints. Pressure will make all of these worse, so note them first.
2. Prepare and protect. Move pot plants, furniture and cars; close windows and doors; cover power points and outdoor lights; wet down garden beds; and block or bund nearby stormwater drains. Our guide to preparing your property for pressure cleaning.
3. Set up and gear up. Check the hose and fittings for damage, choose the nozzle, and put on eye protection, gloves, long pants and enclosed boots (plus hearing protection for petrol machines).
4. Pre-treat. Apply degreaser to oil stains and mould treatment to green or black growth at low pressure, and leave it to dwell without drying.
5. Try your chosen pressure and nozzle on a hidden patch and check for etching, furring or lifted paint.
6. Keep the lance moving in straight, overlapping passes at a steady distance. Work top to bottom on walls; use a surface cleaner on flat concrete for an even finish.
7. Rinse and inspect. Rinse away detergent and loosened grime, then check for stripes or missed patches and touch them up.

Capture the wash water and finish. Collect or contain dirty water rather than letting it reach the gutter (see the NSW rules below), then let the surface dry. Sealing pavers or concrete afterwards helps keep stains out  see what to do after pressure cleaning.

Environmental rules on wastewater and detergents

Many cities and environmental agencies treat pressure washing wastewater as a potential pollutant, especially when it contains oils, heavy metals, paint residue, or detergents. Common rules include:

• No discharge of pressure washing wastewater to storm drains or surface waters.
• Limits on what can go to the sanitary sewer without pre-treatment.
• Specific containment and filtration rules apply when removing lead-based paint or other hazardous coatings.

Universities and large sites often publish pressure washing pollution prevention guidelines that show simple methods to block drains, capture wash water, and dispose of it safely.

Always check your local environmental rules before you start, especially if you use strong chemicals or clean large areas.

Safety and the rules in NSW

The main risks

• Injection injuries. A high-pressure jet can force water and dirt under the skin. Even if the wound looks small, it needs urgent medical attention.
• Eye injuries from flying grit, chips of concrete and splashback.
• Slips on wet, soapy surfaces, and kickback from the gun pushing you off balance.
• Electrical hazards from spraying near power points, lights or extension leads.
• Never use a pressure cleaner from a ladder — the recoil can knock you off. Work at height needs proper access equipment.

Basic safety controls

• Wear safety glasses or goggles, waterproof gloves, long pants and enclosed boots; add hearing protection for petrol machines.
• Never point the lance at people or pets, and keep hands and feet out of the jet.
• Use both hands on the gun at higher pressures and keep stable footing.
• Use outdoor-rated leads and a safety switch (RCD), and keep all plugs and connections out of the spray zone.

For businesses, Safe Work Australia’s guide to managing the risks of high pressure water jetting  covers risk assessment, training, PPE and equipment checks, and AS/NZS 4233.1 sets the safety requirements for high-pressure water jetting systems.

Water use rules in Greater Sydney

Acoording to the Sydney Water’s Water Wise Guidelines apply all year. They restrict cleaning paths, driveways and other paved areas with water to specific situations, such as safety, health or surface contamination, and they don’t allow water to run off onto paths or hard surfaces. Check the current guidelines before cleaning a driveway.

Wash water and stormwater drains

Stormwater drains in Sydney flow untreated into creeks, rivers and the harbour. Letting dirty wash water, detergent, oil or paint residue into a drain is pollution, and councils can fine both individuals and businesses for it. In practice that means:

• Block or cover nearby drains before you start.
• Direct wash water onto lawn or garden where it can soak in, if it contains only water and a small amount of biodegradable detergent.
• Collect heavily contaminated water (oil, paint residue, strong chemicals) and dispose of it through an approved method rather than the drain. Businesses discharging to sewer may need approval from Sydney Water.

Our DIY pressure cleaning safety guide goes through each of these in more detail.

DIY or professional?

Plenty of pressure cleaning is a reasonable weekend job. The deciding factors are surface, size, height and what happens to the wash water. Below table show complete compariion why you need to hire professional company like westlink cleaning services and do it yourself.

DIY usually works when	A professional is usually the better choice when
The surface is durable, such as a small concrete path or patio	The surface is timber, render, painted, heritage brick or a roof
You can reach everything from the ground	The job involves height, ladders or roof access
A light-duty electric machine is enough	It’s a large driveway, multi-level home, strata common area or commercial site
Wash water can be kept out of drains easily	Oil, paint residue or chemicals mean wash water must be captured
You’re comfortable with the safety gear and manual	You need insurance, documented safety procedures or a guaranteed finish

Damage is the hidden cost of DIY: repainting a wall, replacing deck boards or fixing a leaking roof costs far more than the clean itself. If you’re weighing it up, our pressure cleaning cost guide shows what affects the price.

Conclusion

Pressure cleaning works best when you balance pressure, flow and technique rather than chasing the highest number. Start wide and far, test first, and use detergent or soft washing where water alone isn’t enough or the surface is delicate. If you’re in Sydney, check the Water Wise Guidelines and keep wash water out of stormwater drains.

Frequently Asked Questions

What PSI do I need to clean a concrete driveway?

Most concrete driveways clean well at about 2,000–2,800 PSI (140–195 bar) with a 25° nozzle or a surface cleaner. Newer, hard concrete handles the upper end; older, weathered or decorative concrete should stay lower. Test a corner first and keep the lance moving to avoid stripes.

Can pressure cleaning damage concrete or pavers?

Yes. Too much pressure or a narrow tip held close can etch lines into concrete, expose the aggregate and blow the sand out of paver joints. Use a wide tip or surface cleaner, keep a steady distance and re-sand pavers after cleaning. If a stain won’t shift at a safe pressure, use a detergent and dwell time rather than more force.

Am I allowed to pressure clean my driveway in Sydney?

Sydney Water’s Water Wise Guidelines apply year-round and restrict cleaning paved areas with water to specific situations, such as safety, health or surface contamination. Check the current guidelines on Sydney Water’s website before you start, and always keep wash water out of stormwater drains.

Is an electric pressure cleaner strong enough for brick walls, or do I need petrol?

For most brick walls, an electric machine is enough — and often safer. Brick and especially mortar joints are damaged by too much pressure, so the job is usually done at 800–1,500 PSI (55–105 bar) with a 40° tip and a suitable cleaner. Petrol machines suit large areas of hard concrete, not brickwork.

Which detergent should I use for mould and algae?

Use a cleaner labelled for mould, mildew or algae on the surface you’re cleaning, apply it at low pressure, and leave it for the dwell time on the label before rinsing. The chemical does the killing; pressure only rinses. Protect plants, avoid mixing products, and choose biodegradable options where you can.

How often should a house exterior be cleaned in Sydney?

Every one to two years suits most homes. Houses near the coast, under trees or on busy roads usually need it more often because salt, organic growth and traffic grime build up faster. Gentle, regular cleaning does less harm than an aggressive clean every few years.

How much water does pressure cleaning use?

It depends on the machine’s flow rate and how long you spray. A typical home unit uses about 5–9 litres per minute, so an hour of spraying uses roughly 300–540 litres. That is generally less than a garden hose running for the same time, because a hose often flows faster.

Is pressure cleaning safe for roofs?

High-pressure cleaning isn’t recommended for most roofs. It can force water under tiles, strip coatings and void roof warranties, and working on a roof brings a serious fall risk. Soft washing with the right treatment, carried out from proper height-safety access, is the safer method.