You had the driveway cleaned. It looked excellent. Three months later the green is back, in the same places, and it feels like the clean did not work.
It probably did work — on the part it was asked to do. The issue is that most cleaning removes growth without killing it, and in Brisbane’s climate that difference shows up fast.
Mould is not dirt
This is the whole thing. Dirt sits on a surface and pressure removes it. Mould, algae and lichen are organisms with structures anchored into the pores of the concrete.
Pressure removes the visible top layer. What remains below the surface is still alive, and it regrows from an established base rather than from scratch. That is why regrowth is faster the second time, and why it comes back in exactly the same patches.
Killing it requires a treatment that penetrates and stays in contact long enough to work — which is chemistry and dwell time, not force. We cover the method in removing mould from concrete.
The four conditions it needs
Growth returns where all four of these persist, so each is a lever:
- Moisture — the big one. Surfaces that stay damp grow things.
- Shade — UV suppresses growth, so the south side and under trees go first.
- Nutrients — leaf litter, pollen, organic debris.
- A porous surface — somewhere to anchor.
You cannot change Brisbane’s humidity. You can often change drainage, shade and debris, and those are what determine whether a clean lasts one season or several.
Why it comes back faster in some spots
The pattern tells you the cause. Growth that returns first along one edge usually means water is not draining there. A band under the eaves line often means run-off is concentrating. Patches under a tree are nutrients plus shade.
Treating those patterns as a drainage or vegetation problem, rather than a cleaning problem, is what actually breaks the cycle. Cleaning the same spot every eight months is treating the symptom.
What extends the interval
- Kill rather than remove. A proper biocidal treatment with adequate dwell time is the single biggest factor.
- Fix pooling. Anywhere water sits for more than a day after rain will regrow first.
- Cut back overhanging vegetation to reduce both shade and leaf litter.
- Clear debris regularly. Leaves on concrete for a week leave a nutrient patch behind.
- Consider sealing. A sealed surface is less porous, giving growth less to anchor to — though it must be applied to clean, fully dry concrete.
Realistic expectations
Nothing makes concrete permanently immune. In a subtropical climate, exterior surfaces will regrow eventually, and anyone promising otherwise is overselling.
The honest measure is the interval. A clean that only removes growth might hold a few months in a shaded spot. One that kills it, on a surface with reasonable drainage and sun, can hold for years. That range is the difference the method makes.
If your surfaces are regrowing faster than they should, request a free quote and we will look at why — including whether the cause is drainage rather than cleaning.
