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Bathroom Leak Water Damage and Mould Remediation in Campsie NSW: Targeted Heat Drying a Rendered Wall
By Michael Nguyen | Indoor Environmental Professional (IEP) | IICRC WRT, AMRT, ASD (69486970) | Mould Testing Technician (NAT10913005) | Licensed Builder NSW 392154C (Supervisor, KBL+RENO)
A leaking bathroom does not always show up in the bathroom. In this Campsie job, water from a failed bathroom waterproofing system had soaked into the adjoining rendered wall, causing water damage, flaking paint and mould growth on the other side.
Here is how our team removed the damaged surface, cleaned up the mould and set up a targeted heat drying system to dry the wall properly, following IICRC standards.
What We Found
The painted rendered wall next to the bathroom was stained, bubbling and showing visible mould growth along the lower section. Moisture readings taken across the wall confirmed the masonry was wet well beyond the visible damage, and we marked those readings directly on the wall to map the affected area.
The paint on the wall was trapping moisture inside the render, which slows drying and gives mould the damp surface it needs to grow. If you are seeing similar signs at home, a mould and moisture inspection is the best place to start.
Our Mould Remediation and Drying Process
Step 1: Grinding Back the Painted Render
We ground the paint off the affected section of wall using a grinder fitted with a dust shroud, connected to a Husqvarna HEPA dust extractor. This captures the dust and mould spores at the source instead of letting them spread through the home. Our technician wore full PPE, including disposable coveralls, a half-face respirator and gloves.
Removing the paint does two things. It takes away the mould-affected surface, and it opens up the render so trapped moisture can escape during drying.
Step 2: HEPA Sandwich Mould Clean-Up
Next, we cleaned and treated the mould using the HEPA sandwich method, a common approach in professional mould remediation:
HEPA vacuum the surface to remove loose spores and debris.
Damp wipe and treat the surface to remove remaining mould residue.
HEPA vacuum again to collect anything loosened during cleaning.
This follows the principles of the IICRC S520 Standard for Professional Mould Remediation: remove the mould, do not just cover it up.
Step 3: Setting Up a Closed Drying System
We are setting up a closed drying system, as outlined in the IICRC S500 Standard for Professional Water Damage Restoration. The drying area is closed off from outside air so we can control the conditions inside it. A desiccant dehumidifier removes moisture from the air, keeping humidity low so the wall can keep releasing water.
Step 4: Targeted Heat Drying with the Drymatic System
Masonry and render hold water deep inside, so standard air movers alone are slow. We are using the Drymatic thermal targeted drying system: a heat bar warms the airflow, and Drymatic drying mats direct that warm air onto the wet section of wall.
Heating the wall helps drive moisture out from inside the masonry to the surface, where the desiccant dehumidifier captures it. Targeting the heat means we dry only the affected area rather than heating the whole house.
Why a Rendered Masonry Wall Takes 3 to 4 Weeks to Dry
Brick, block and render are dense materials that absorb water slowly and release it slowly. Under IICRC S500, these are treated as specialty drying situations, where moisture is bound deep inside the material and takes longer to remove.
We are aiming to dry this wall in about 3 to 4 weeks. During that time we monitor moisture readings regularly and adjust the equipment until the wall reaches its drying goal. Rushing this step and repainting too early can lead to paint failure, salt damage and mould coming back.
Signs Your Bathroom Is Leaking Into the Wall
Bubbling, flaking or peeling paint on walls next to a bathroom or shower
Dark staining or tide marks near the bottom of the wall
Musty smells in rooms next to the bathroom
Swollen or damp skirting boards and timber floors
Mould spots that come back after cleaning
Hidden leaks behind bathrooms are something we see often. Read about the hidden black mould we found behind a bathroom wall in Bexley North and our bathroom leak make safe in Blaxland.
Mould Remediation and Water Damage Drying in Campsie and Sydney
AAA Mould Removal provides mould remediation and water damage restoration in Campsie, the Inner West and across Sydney. Once drying is complete, we can carry out post-remediation mould testing to confirm the area is clean.
For a recent commercial job, see our emergency water damage response at Nepean Hospital.
Frequently Asked Questions
Why remove the paint from a wet wall?
Paint acts like a barrier that traps moisture inside the render. Removing it from the affected area lets the wall dry much faster and removes the mould-affected surface.
Can I just paint over mould?
No. Painting over mould hides it but does not remove it, and mould will usually come back through the new paint if the wall is still damp. Learn more about the risks of toxic black mould.
What is a HEPA sandwich?
It is a cleaning method of HEPA vacuuming, damp wiping and HEPA vacuuming again. It removes mould spores and residue without spreading them around the home.
How long does a masonry wall take to dry?
It depends on how wet the wall is and what it is made of. Rendered masonry walls like this one usually take several weeks. We are aiming for 3 to 4 weeks on this job.
Will the leak come back?
If the bathroom waterproofing is not fixed, yes. The source of the water needs to be repaired, otherwise the wall will get wet again. As licensed builders with a Kitchen, Bathroom and Laundry renovation licence, we can advise on the repairs needed.
About the Author
Michael Nguyen is the director of AAA Mould Removal and leads our water damage and mould remediation work across Sydney. His qualifications include:
Indoor Environmental Professional (IEP) – Testing Water-Damaged Buildings, Australian College of Environmental Studies (RTO 21740), 2026. Includes nationally recognised units NAT11429003 Conduct a comprehensive mould and moisture assessment and NAT11429007 Conduct post remediation verification mould testing (11429NAT Advanced Diploma of Building Biology)
IICRC Water Damage Restoration Technician (WRT)
IICRC Applied Microbial Remediation Technician (AMRT)
IICRC Applied Structural Drying (ASD), IICRC no. 69486970
Mould Testing Technician (NAT10913005)
Licensed Builder NSW 392154C (Supervisor, Kitchen, Bathroom & Laundry and Renovation)
Carpentry Licence
Worried About Mould or a Leaking Bathroom?
Call AAA Mould Removal on 1300 739 783 or contact us online. We will find the moisture, remove the mould properly and dry your home to IICRC standards.
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