Your driveway turned green: blame the shade side
The green film on your driveway is algae, and it grows where concrete stays damp — the shaded side, under the tree canopy, wherever the sun never quite reaches. It is slippery when wet and it will not scrub off with a broom. A proper pressure clean removes it; most Sydney driveways run $180-$420, and a seal afterwards slows the regrowth.
The film, not the stain
That green is alive. It is algae — a film of simple organic growth that settles anywhere concrete stays damp for long enough. The spores are always in the air; they only take hold where moisture lingers. Concrete suits them perfectly. It is porous, it holds water after rain, and on the shaded side of a house it can stay wet for days. The green is not dirt working its way in. It is a living layer sitting on top of the slab.
That distinction is good news. A surface film comes off. This is not rust, not salt attack, not a stain that has soaked into the concrete — it is an organic layer that lifts under proper pressure cleaning, and the slab underneath is usually in better shape than the green suggests. What cleaning cannot do is change the conditions that grew it. Which is why the second half of this story matters as much as the first.
The shade-side pattern in canopy suburbs
Walk a street in Wahroonga, St Ives, Killara or Pymble in late winter and you can read the sun on the driveways. The open, north-facing runs stay grey. The southern strips, the sections under the tree canopy, the concrete hemmed in by the house or the neighbour's fence — those go green first. The canopy that makes these suburbs worth the mortgage is the same canopy that stops the slab beneath it from ever fully drying.
The pattern repeats east of the bridge with different causes. In Mosman or Vaucluse it is the boundary wall and the two-storey neighbour throwing the shade, not the liquidambar. The mechanism is identical everywhere: concrete that sits in shadow through a wet Sydney winter never dries between rains, and damp concrete is where the film establishes, thickens, and turns a pale driveway the colour of a pond.
Slippery first, ugly second
The practical problem arrives before the cosmetic one. Wet algae is genuinely slippery, and a green driveway on a slope is at its worst on exactly the mornings you are hurrying to the car in the rain. Flat paths are more forgiving, not exempt. This is not a reason for alarm — it is a reason to book the clean before winter sets the film, rather than after someone tests it.
Home remedies underdeliver. A stiff broom smears the film around. Household bleach from a watering can pales it for a few weeks, then it returns, because the moisture and the shade have not gone anywhere. The honest version: no clean changes your driveway's aspect. What a proper clean does is take the surface back to bare. What a seal does afterwards is slow the regrowth — sealed concrete sheds water instead of drinking it, so the film has far less to hold onto.
The fix, the seal and the number
Concrete is one of the few surfaces on your property built to take real pressure, so this is a genuine pressure-cleaning job — fan tips, even passes, edges and joints included, the slurry rinsed away rather than pushed onto the lawn. Sealing is an optional set add-on, and on a shade-side driveway it earns its keep, because the surface stops holding the moisture the algae needs to come back.
Schmick's driveway and path pressure cleaning starts at $180, and most Sydney driveways land between $180 and $420 depending on area, with sealing priced as a set add-on. You do not need a site visit to find out where yours sits — the instant quote returns a firm, bookable price in about 60 seconds, and it holds unless the place is materially different from what you described.