Pressure cleaning before driveway sealing on the Central Coast.

Cleaning and surface preparation are not the same thing.

A driveway can look bright and still be unsuitable for sealer. Pressure removes loose dirt, but it may leave oil in the pores, old coating at the edges, detergent residue in low spots and moisture deep in joints. Adhesion depends on removing the contamination that matters to the selected product, then allowing the surface to dry to the manufacturer’s limit.

Before cleaning, identify the substrate and old finish. Plain concrete, coloured concrete, exposed aggregate, clay pavers, concrete pavers and natural stone react differently. Unknown paint or coating deserves a test before any aggressive removal. If an old film is peeling, pressure washing alone is not a complete removal method. Use the failed sealer repair guide instead.

What each common stain needs.

Loose soil and road film: pre-wet nearby plants, use an even surface-cleaning pattern, then rinse without leaving dirty lines at edges. A rotary surface cleaner usually produces a more even result than drawing stripes with a wand.

Oil: absorb fresh liquid first so water does not spread it. Apply a compatible degreaser at the stated dilution, allow roughly 10 to 20 minutes of dwell without letting it dry, agitate, then recover the wash. Old oil can penetrate deeply and may remain as a shadow after treatment.

Leaf tannin and gum marks: use a substrate-compatible treatment rather than extreme pressure. These are common under spotted gums around Gosford, Erina and Wyoming. The right chemistry can remove colour without opening the concrete surface.

Moss and algae: kill growth as directed, remove the dead material and correct the shade or water source where practical. A clean surface that stays wet will become green again. On steep or shaded sites, consider a finish covered by the anti-slip coating service.

Rust and battery stains: identify the source and test a specialist treatment in a small area. Acid can alter coloured concrete and expose aggregate, while runoff can damage metal, gardens and waterways. Deep rust may improve without disappearing.

Efflorescence: dry white salt is not ordinary grime. Determine whether it is from new pavers, ground moisture or coastal exposure before treatment. Sealing over an active moisture path can trap a pale stain beneath the film.

Pressure: enough to clean, not enough to cut.

Domestic machines are often around 1,800 to 2,500psi, while commercial units may operate around 3,000 to 4,000psi with substantially more water flow. Those figures do not describe cleaning quality on their own. Nozzle angle, distance, flow, dwell, surface hardness and operator speed decide whether the result is even.

A fine jet held 100 to 200mm from the slab can carve soft surface paste, reveal aggregate and leave permanent writing marks. The same jet can throw all joint sand from pavers. Start with a broad fan, a generous distance and a hidden test area. Clean systematically with overlapping passes, never use skin or a hand to test the jet, and keep people, pets, glass and electrical fittings clear.

The runoff rule is simple.

Central Coast stormwater is not a sewer and is generally not treated before reaching local waterways. Council’s own water guidance notes that driveway and vehicle wash can carry oil, rubber, metals and cleaning chemicals into the nearest drain. Under the NSW Protection of the Environment Operations Act 1997, polluted water must not be allowed to enter waters.

A compliant workflow dry-sweeps first, covers or blocks nearby pits, uses absorbent socks or temporary bunding, recovers dirty liquid where needed and collects solids before the area is rinsed. Water containing detergent, oil, paint residue, herbicide, dissolved sealer or heavy sediment does not become clean merely because it has been diluted. Ask the contractor where the recovered material goes.

How dry is dry enough?

For ordinary concrete, allow at least 24 to 48 dry hours after pressure cleaning. Deep paver joints, exposed aggregate pockets, cracks and shaded south-facing areas may need longer. After heavy rain or cool humid conditions, 72 hours can be the safer window. Product data sheets override a rule of thumb, particularly for moisture-sensitive film-forming coatings.

Visual colour is only a first check. Inspect joints and cracks, lift mats or objects well before work, and watch for new darkening from below. Do not coat while morning dew remains. The preferred months and temperature tradeoffs are covered in the Central Coast sealing calendar.

Realistic 2026 preparation costs.

Routine pressure cleaning before sealing is commonly $4 to $9 per square metre. Small jobs often carry a $300 to $500 minimum. Heavy moss, detailed oil or rust treatment, paver-joint work and wastewater recovery can bring preparation to $8 to $18 per square metre.

For a 60m² driveway, ordinary cleaning is roughly $300 to $540, while detailed contamination treatment can be $480 to $1,080. Access, water supply, slope, nearby drains, surface type and whether the work is bundled with sealing all move the total. Many sealing quotes include routine cleaning, so ask for the preparation allowance rather than paying twice. Compare the final figure with the 2026 driveway cost guide.

Routine pressure cleaning and like-for-like sealing do not need Central Coast Council approval. There is also no general NSW rebate for private driveway cleaning or sealing. Current water restriction requirements can change, so the contractor should check Council’s rules for the work date and use water efficiently regardless of the restriction level.

DIY or professional preparation?

DIY is reasonable for light soil on sound plain concrete when the area is level, runoff can be controlled and the sealing contractor agrees with the preparation. Wear enclosed footwear, eye protection and hearing protection, keep both hands on the equipment and stop if the hose, fittings or electrical supply are damaged. Never point the jet at skin because high-pressure injection injuries can look small while causing serious deep damage.

Use a professional when the surface has an unknown coating, widespread oil, rust, moss on a steep grade, loose concrete, deep paver joints or a drain at the low point. The line is also reached when you cannot lawfully contain the wash water. Saving several hundred dollars on cleaning is poor value if etched lines remain visible beneath every future clear coat.

What to demand in a sealing quote.

The quote should state the cleaning method, stain treatments, runoff controls, crack or joint work, drying allowance and what staining may remain. It should name the sealer, the required surface condition and who decides whether the slab is dry enough. “Pressure clean and seal” is not a specification.

Photograph the cleaned surface before coating and ask the contractor to flag any stain that will remain visible. Confirm the weather contingency and vehicle return time in writing. A good job can wait for dry concrete. A cheap job relies on the booking calendar.