Why your south-facing render turns green (and how to fix it properly)
The green on south-facing render is algae — a living organism rooted in the render's pores, fed by shade and damp that a south wall never fully sheds. Pressure washing etches the surface and spreads the spores; a soft wash kills the growth at the root. Schmick house soft washes start at $300, with most single-storey homes landing between $420 and $960.
Green is a plant, not a stain
The green film on your render is not dirt, and it did not blow in. It is algae — a living colony, often with mould behind it — and it is growing there because render is the perfect host. Render is porous. It holds moisture in millions of tiny voids, and once spores settle, the growth anchors below the surface, not on top of it. What you see is the canopy. The roots are in the wall.
That distinction decides everything about the fix. A stain sits on a surface and can be washed off. An organism rooted in a porous surface has to be killed, or it simply regrows from whatever the rinse left behind. Treat green render like dirt and you are mowing a lawn — it looks fine for a few weeks, then the wall greens over again, usually faster than before.
The south wall always goes first
In Sydney the pattern is predictable. South-facing walls get the least direct sun, so they dry last after rain and hold overnight dew longest. Shade plus persistent damp is the entire recipe for algae, which is why the south side of a house can be green while the north side, in identical render, stays clean for years. The wall is not dirtier. It is just wetter, for more hours of every day.
Landscaping finishes the job. A murraya hedge grown hard against the wall, a jacaranda canopy overhead, a neighbour's fence a metre away — each one blocks sun and kills airflow, and the render behind it never properly dries. The pattern repeats from the tree canopy of the North Shore to the hedge-lined blocks of Vaucluse and Bellevue Hill: the wall you never see from the street is the one quietly going green.
The pressure washer makes it worse
The instinct is to hire a pressure washer and blast it. The green does come off — along with the surface. Render is soft. A lance held close enough to strip algae also etches the finish, opening the pores wider and leaving wand marks that show every time the sun rakes across the wall. The texture you paid a renderer to trowel on does not survive a close-range blast.
Worse, the growth comes back faster. Blasting removes the visible canopy but not the roots seated in the render, and the spray carries spores across the rest of the wall as it works. The etched surface now holds more water than it did before, so regrowth finds better conditions than the original colony had. Six months later the wall is green again — and this time it is scarred underneath.
Soft washing kills it at the root
Soft washing takes the opposite approach: low pressure, the right cleaning solution for the surface, and dwell time. The solution soaks into the pores and kills the organism through its full depth — roots included — then a gentle rinse carries the dead material away. The render finish is never touched by force. Because nothing living is left behind, the wall stays clean for years rather than months.
One honest caveat: soft washing fixes growth, not render. Hairline cracking, drummy patches that sound hollow when tapped, paint that has chalked through — those are a renderer's problems, and no wash will hide them. Sometimes a clean reveals them, because the green was covering the evidence. If that is what we find, we say so plainly. What a soft wash fixes, it fixes properly: the wall comes back to its actual colour and stays there.
What fixing it properly costs
The numbers are plain. A Schmick house soft wash starts at $300, most single-storey homes land between $420 and $960 depending on wall area, and a second storey adds about 40% for the access and time. The south wall is not a surcharge — it is simply part of the house, treated with the same solution and the same patience as every other elevation.
You do not need someone standing in your garden squinting at the green to price it. Answer a few questions about the house in the instant quote and you get a firm, bookable price in about 60 seconds — and it holds unless the place is materially different from what you described. The algae took years to establish. The decision to remove it properly takes about a minute.