Why the mould comes back a month after cleaning
You blast the black spots off and they're back in a month. Why pressure alone leaves the roots behind, and what keeps mould from coming straight back.
The assumption we're testing
“If it looks clean, it is clean.”
What you see is the top of it
Mould, algae and lichen grow into a surface, not just on it. Render, concrete and timber are full of tiny holes. The growth puts roots down into them.
A jet of water takes off the part you can see. The roots stay. Give them a damp week and some shade, and the spots come back in the same places.
Why it keeps picking the same spots
Growth needs damp and shade. That's why the south wall goes green and the north wall doesn't. It's why the path under the big tree stays dark.
Round Sydney, humid summers make it worse. A wall that never gets sun can stay damp for days after rain.
What actually stops it
Kill it before you wash it. A cleaning mix goes on at low pressure and sits for a while. It kills the growth down into the surface. Then it gets a gentle rinse.
It will still come back in the end. Nothing stops mould for good on a shady, damp wall. But killed at the root, it takes much longer to return than after a blast.
You can slow it down too. Trim plants back from the walls. Clear leaf piles away from paths. More sun and air means less damp.
When it isn't mould at all
Some white marks are efflorescence. That's salt coming out of brick or concrete as it dries. It looks like white powder or crust. It isn't alive, so a mould treatment won't touch it.
Dark marks can also be plain dirt or leaf stains. That's why the mark gets treated for what it is before anything gets washed.
See our mould and stain removal page, or get a free quote. We'll tell you what the marks are and what it will take to shift them.
Want it done without the risk? We'll check the surface first, then pick the method.