A property manager calls us. There’s mould on a wall in a tenanted unit. They’ve had a cleaner spray it down twice already. It keeps coming back. Can we “clean it properly”?
It’s a fair question. And the answer is: no - because that’s the wrong job for the situation. What they need isn’t cleaning. It’s remediation. And the difference matters.
The short version
- Cleaning treats the symptom: remove the visible growth, surface-disinfect, leave it dry.
- Remediation treats the cause: contain the affected zone, address the moisture source, remove or encapsulate substrate that can’t be saved, and verify the outcome with post-works sampling.
Cleaning is appropriate for nuisance growth on a non-porous surface in a space that’s dry and well-ventilated. Anything beyond that - and certainly anything that’s come back twice - is a remediation job.
Why “just clean it again” doesn’t work
Mould isn’t dirt. It’s a living organism that grows where it has three things: a porous substrate, moisture, and time. If you only address the visible growth (the surface), you’ve left the substrate, the moisture, and any spores that already migrated into the cavity. So it comes back. Always.
This is why a competent remediation scope has these four pieces, and a cleaning scope only has the first one:
- Containment - physical and HEPA-filtered separation between the affected zone and the rest of the building, so spores don’t migrate during the works.
- Source control - identifying and fixing the moisture event that caused the growth in the first place. A roof leak, a plumbing fault, a ventilation deficiency, a thermal bridge.
- Substrate removal or encapsulation - porous material that’s contaminated past saving comes out. Surfaces that have to stay get cleaned and sealed.
- Verification - post-remediation air or surface sampling with a NATA-accredited lab, so the outcome is documented.
When cleaning is genuinely enough
There are situations where surface cleaning is the correct scope:
- Light surface mildew in a well-ventilated wet area (a bathroom, a laundry) on non-porous tile or glass
- Spotty growth on a sealed paint surface in a space that’s otherwise dry
- Localised mould on a hard surface that you can verify is dry behind
Even then, you should treat the underlying ventilation issue. If a bathroom is growing mould, the extract fan probably isn’t pulling enough air, or it’s being run for thirty seconds when it needs ten minutes.
How to tell what you’re dealing with
A few quick questions:
- Has it come back after cleaning? If yes, you have a remediation job.
- Is the growth larger than the size of a sheet of A4? If yes, you almost certainly have a remediation job.
- Is it on or behind a porous substrate (plasterboard, timber, fabric, insulation, carpet underlay)? If yes, treat as remediation.
- Is there a moisture source you haven’t identified? If yes, remediation, plus the moisture source investigation, plus follow-up testing.
If you answered yes to any of those, mould testing before scoping the work will tell you what you’re actually dealing with - and it’s independent, so you can use any remediator afterwards.
What this looks like in practice
A typical remediation scope on a single bedroom-sized zone runs 2–4 days on site: a day for setup and containment, a day or two for removal and treatment, half a day for drying verification and clearance sampling. A larger multi-zone job can run weeks. The point is - every step is documented, so the outcome is something you can defend at audit.
If you’re dealing with a recurring mould problem and the “clean it again” cycle isn’t working, get in touch. We’ll scope what’s actually needed and tell you up-front what the right job looks like.