How to Pressure Clean Exposed Aggregate Pavers Like an Expert

Exposed aggregate pavers are a popular choice across Adelaide for driveways, alfresco areas, pool surrounds and pathways. Their textured finish of pebbles set in concrete is durable and slip-resistant, but the same texture traps dirt, moss, lichen, oil and tannin stains. Pressure cleaning is the most effective way to restore them, but only if it is done correctly. Too much pressure, the wrong nozzle or poor technique can strip the cement surface, loosen the stones and leave streaky results. This guide explains how to pressure clean exposed aggregate pavers properly, with Adelaide's climate and conditions in mind.

Understanding Exposed Aggregate Pavers

Exposed aggregate is made by removing the top layer of cement paste from a concrete surface so the stones underneath are revealed. The stones are held in place by the surrounding cement matrix. Over time, and especially when the surface is blasted with excessive pressure, that cement can erode, leaving the aggregate loose or protruding unevenly.

Adelaide's hot, dry summers and mild, wet winters create ideal conditions for different types of build-up:

Moss and algae: Common in shaded, south-facing areas and near garden beds during the cooler, wetter months.
Lichen: Clings tightly to the surface and often needs a treatment before pressure cleaning.
Tannin stains: Caused by leaves from gum trees, jacarandas and other deciduous plants.
Oil and grease: Typical on driveways and carport slabs.
Rust stains: Often from metal furniture, pots or irrigation water with high iron content.
Efflorescence: White, powdery salt deposits that rise to the surface, sometimes seen on newer paving.

Equipment You Need

Pressure Washer Specifications

For exposed aggregate, a pressure washer in the range of 2,000 to 3,000 PSI (roughly 14 to 20 MPa) is generally suitable for residential surfaces. Commercial-grade machines can exceed this, but higher pressure is not necessarily better. A flow rate of around 8 to 12 litres per minute helps rinse debris away efficiently without relying on excessive force.

Nozzles and Attachments

Choosing the right nozzle is one of the biggest factors in a quality result:

A 25-degree fan nozzle is a safe starting point for general cleaning.
A 15-degree nozzle can be used cautiously on stubborn stains, held at a greater distance.
A surface cleaner attachment (a rotating flat-head cleaner) delivers even results and reduces the risk of striping. It is highly recommended for large driveways and patios.
Avoid zero-degree (red) pencil-jet nozzles entirely, as they can gouge the surface and dislodge stones.

Other Items

You will also need a stiff-bristle broom (not wire), a garden sprayer for applying treatments, a hose, protective eyewear, closed-in non-slip footwear, gloves and hearing protection. If you are using chemicals, keep a supply of water on hand to dilute and rinse them.

Preparation Before You Start

Good preparation prevents most common problems and protects your property and garden.

Clear the area. Remove furniture, pots, toys, doormats and vehicles.
Sweep thoroughly. Remove loose leaves, dirt and debris so the pressure washer is not simply pushing grit around.
Inspect the surface. Check for loose stones, cracks, crumbling edges or failed joints. Damaged areas should be repaired after cleaning, and weak spots should be treated with a lower pressure.
Protect plants and garden beds. Wet nearby plants with fresh water and cover delicate ones if you will be using cleaning solutions.
Test a small area. Try your chosen nozzle and pressure in an inconspicuous spot to confirm it cleans without damaging the surface.
Check drainage. Know where wastewater will flow and keep it away from doors, garages and neighbouring properties.

Pre-Treating Stains and Biological Growth

Pre-treatment does much of the hard work and allows you to use lower pressure, which is safer for the aggregate.

Moss, Algae and Lichen

Apply a masonry-safe biocide or a diluted sodium hypochlorite solution using a low-pressure sprayer, following the product label. Allow it to dwell for the recommended time, typically 10 to 20 minutes, without letting it dry on the surface. On heavily infested areas, lichen may require a second application or a longer dwell time. Always keep the surface damp in Adelaide's hot, dry weather so the product does not dry out and leave residue.

Oil and Grease

Apply a concrete degreaser to fresh oil spots and agitate with a stiff broom. For older stains, a poultice made from an absorbent material and a solvent-based degreaser can draw oil out of the pores. Rinse thoroughly afterwards.

Tannin and Rust

Tannin stains often respond to an alkaline cleaner or a mild oxygenated bleach product. Rust stains generally need a rust remover designed for concrete or masonry, which may contain oxalic or phosphoric acid. Take care with acids on exposed aggregate, because strong acids can etch the cement and dull the stones. Always test first and rinse thoroughly.

The Pressure Cleaning Technique

Work in a Consistent Pattern

Begin at the highest point of the surface and work downhill so dirty water runs away from cleaned areas. Keep the nozzle at a consistent distance, usually 20 to 40 centimetres, and move in smooth, overlapping passes. Starting further away and moving closer as needed is safer than starting up close.

Use a Surface Cleaner Where Possible

A surface cleaner attachment keeps the spray at a uniform height and angle, which prevents the zebra-striping that often occurs with a handheld wand. It also uses water more efficiently and speeds up large jobs. Use the wand with a fan nozzle only for edges, steps and tight corners.

Keep the Wand Angle Low and Steady

Hold the wand at roughly 30 to 45 degrees to the surface rather than pointing it straight down. This lifts dirt out of the textured gaps without driving water and force directly into the cement matrix. Avoid lingering in one spot, since this can create pale patches or etch the surface.

Pay Attention to the Joints and Edges

If the pavers are laid with joints, high pressure can wash out the jointing sand or mortar. Use lower pressure around joints and plan to re-sand or re-fill them afterwards. Around expansion joints and edges, reduce your pressure further to avoid chipping.

Rinsing and Final Checks

Once the surface is clean, rinse it completely so no chemical residue is left behind. Residue can cause slippery patches, discolouration or plant damage. Allow the surface to dry fully, then inspect it in different light. Streaks, missed spots and remaining stains are easier to see once the paving is dry, and any problem areas can be re-treated at this stage.

Sealing After Cleaning

Sealing is the step that most often separates a short-lived clean from a long-lasting one. A quality penetrating or film-forming sealer designed for exposed aggregate helps resist oil, water, tannin and biological growth, and can enhance the colour of the stones. Key points to remember:

The surface must be completely clean and dry, ideally for at least 24 to 48 hours, before sealing.
Choose a sealer suited to the area. Driveways need products that handle hot tyres and vehicle traffic, while pool surrounds benefit from slip-resistant formulations.
Apply in mild weather and avoid direct midday sun, which is a particular consideration during Adelaide's summer heat, as sealers can dry too fast and bubble or streak.
Apply thin, even coats rather than one heavy coat to prevent whitening and pooling.

Most sealed surfaces need reapplication every two to five years depending on traffic, sun exposure and product quality.

Common Mistakes to Avoid

Many damaged aggregate surfaces result from avoidable errors. Using a pressure setting that is too high is the leading cause, followed by holding the nozzle too close to the surface. Other frequent mistakes include allowing chemicals to dry on the paving, cleaning in full sun so products evaporate quickly, neglecting to protect plants, and skipping the sealing step. Using wire brushes can also leave metal particles that later rust and stain the surface.

Environmental and Regulatory Considerations in Adelaide

Wastewater from pressure cleaning should not be allowed to enter the stormwater system, which drains to local waterways and ultimately the Gulf St Vincent. In South Australia, the Environment Protection Act places responsibility on people to avoid polluting stormwater, so it is good practice to direct runoff onto lawn or garden areas where appropriate, or to capture it, especially when using cleaning chemicals. Professional operators often use recovery mats and vacuum systems to collect wastewater. Check current guidance from your local council and the EPA South Australia, as water restrictions and environmental expectations can change. Biodegradable, low-impact cleaning products are increasingly preferred in 2026 and are a sensible choice for home use.

Safety Considerations

Pressure washers can cause serious injuries. Never point the wand at people or pets, keep a firm footing on wet surfaces, and wear eye protection at all times. Use caution near power outlets and extension leads, and do not clean on ladders. Chemicals should be handled according to the safety data sheet, never mixed together (particularly bleach and acids), and stored securely.

When to Call a Professional

DIY cleaning suits small, lightly soiled areas, but there are times when hiring a professional pressure cleaning service in Adelaide is the better option. Consider calling an expert if:

The paving is large, heavily stained or has years of built-up lichen and moss.
The aggregate is already loose or the surface is deteriorating.
You need wastewater captured or are working near sensitive drainage.
The area is difficult to access or includes multiple levels.
You want a professional-grade sealing finish.

Professionals have commercial equipment, surface cleaners, knowledge of the right chemicals and techniques, and public liability insurance for added peace of mind.

Maintaining Your Exposed Aggregate Between Cleans

Regular maintenance reduces the need for aggressive cleaning. Sweep weekly to remove leaves and debris, wash away spills such as oil, wine and fertiliser promptly, trim overhanging vegetation to reduce shade and tannin, and use a mild biocidal wash once or twice a year in shaded areas. Ensuring good drainage and fixing leaking taps or downpipes that continually wet the surface also slows moss https://adelaidepressurecleaningpros.com.au growth.

Final Thoughts

Pressure cleaning exposed aggregate pavers is about control rather than raw power. Choosing the right equipment, pre-treating stains, using a surface cleaner, keeping pressure moderate and sealing the surface afterwards will protect your paving and keep it looking its best for years. With attention to Adelaide's climate, local environmental requirements and safe working practices, you can achieve results that rival a professional finish, or confidently decide when it is time to bring in the experts.

Adelaide Pressure Cleaning Pros

70 Overland Rd, Croydon Park SA 5008

(08) 7228 0262