Mould removal covers two quite different trades at quite different prices, and the quotes people compare are often not for the same thing at all.
We do the exterior side. Being clear about where the line sits saves everyone a call.
Exterior mould — what it costs
Mould, algae and mildew on render, brick, fencing, paths and eaves is a cleaning job, treated by soft washing.
Spot treatment — one shaded wall, a fence run, a section of eaves: commonly $200 to $450.
Full house soft wash including walls, eaves and gutter faces: commonly $600 to $1,500 for a typical detached Sydney home, with two-storey and difficult-access properties at the upper end and beyond.
Paths, driveways and paved areas: quoted on area, usually bundled with the house wash at a better rate than separately.
What moves it: house size, number of storeys, access, how established the growth is, and how much protection is needed for gardens and surrounds. See why two quotes for the same house differ by hundreds.
Our general guidance on reading a quote is in what a fixed written quote should itemise.
Interior mould — a different trade
Interior mould is remediation, not cleaning, and it is governed by a different standard of care because the health exposure is different.
Indicative Sydney ranges:
Inspection and air or surface testing: $400 to $900.
Small area remediation — a bathroom ceiling, one wall: $500 to $1,500.
Significant remediation with containment, negative air, removal of affected plasterboard and insulation: $3,000 to $15,000, and higher where it is extensive.
Plus whatever is causing it — a roof leak, failed waterproofing, a plumbing fault, inadequate ventilation.
The important thing about interior mould is that cleaning it is not the job. Wiping mould off a surface treats the visible symptom while the moisture source keeps it coming back, and disturbing it without containment spreads spores through the house. Proper remediation finds the water, fixes it, contains the area, removes porous material that cannot be salvaged, and verifies afterwards.
Where the line sits
Not always obvious, so:
Exterior cleaning handles: green and black growth on external render, painted walls, brick, Colorbond, fencing, eaves and soffits, paths, driveways, decks and paved areas, and shaded walls where growth has established.
Remediation handles: anything inside the building envelope, anything inside a wall cavity, mould on or behind plasterboard, ceiling mould, mould following a flood or a leak, mould in subfloors or roof spaces, and any situation where someone in the house is reporting symptoms.
The grey zone is the exterior of an enclosed space — the inside face of a sunroom, an enclosed balcony, a garage. Judged case by case.
Often the exterior problem causes the interior one
This is why it is worth understanding both.
A blocked gutter overflowing into the eaves produces interior mould in a top-floor ceiling. A cracked downpipe against a wall produces damp and mould on the inside of that wall. A roof leak around a vent or a skylight shows up as a ceiling stain metres from the actual entry point.
In each case the remediation contractor removes the mould and the problem comes back next winter, because nothing was fixed outside.
Before paying for interior remediation, it is worth having someone look at the gutters, downpipes, roof and drainage. Frequently the exterior fix is a few hundred dollars and it is the actual solution. Our pieces on why gutters overflow and weep holes and subfloor vents cover the two most common culprits.
Why Sydney has so much of it
Humidity, mild winters that never kill growth off, and a lot of housing stock in shaded, damp or poorly ventilated positions.
Worst affected: south-facing walls that get no direct sun, properties under heavy canopy on the North Shore, anything near a lagoon or a gully, and older housing with blocked subfloor ventilation.
The growth is seasonal — it establishes through the wet winter months and becomes obvious in spring, which is when the calls come.
What a proper exterior quote includes
- Soft wash, not high pressure. High pressure on render drives water into the substrate and damages the paint film
- Protection and pre-wetting of gardens, and rinsing afterwards
- Managed runoff rather than straight into the stormwater drain — the rules are here
- Rainwater tank disconnected if applicable
- A fixed written price before work starts
- Photos on completion
We go into the chemistry in what is actually in a soft-wash mix, and into doing it without damaging the paint in removing mould and algae from render.
How long it lasts
A properly soft-washed exterior in Sydney stays clean for roughly two to four years, less on a south-facing wall under trees.
Extending that means dealing with the conditions: cut back vegetation for light and airflow, fix the gutter or the drainage keeping the wall damp, and treat annually with a retail product once it is clean — see our assessment of those.
For a quote on the exterior side, see mould removal or house washing. If what you describe is an interior problem, we will say so and point you to the right trade rather than quote for it.
