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Subfloor Mould Make-Safe in Hazelbrook: Cleaning and Encapsulation Before a Bathroom Rebuild
By Michael Nguyen | Indoor Environmental Professional (IEP) | IICRC WRT, AMRT, ASD (69486970) | Mould Testing Technician (NAT10913005) | Licensed Builder NSW 392154C (Supervisor, KBL+RENO)
Quick answer: In June 2026 we carried out a two-day mould make-safe in the subfloor of a home in Hazelbrook, in the Blue Mountains. We cleaned the surface fungal growth from the subfloor timbers and flooring under the bathroom, where a leaking shower with a failed waterproofing membrane had been wetting the subfloor, then encapsulated the cleaned surfaces so the area stays controlled until the owner's builder rebuilds the bathroom. The job cost $4,500 + GST.
The shower's waterproofing membrane had failed, so water from every shower was leaking into the subfloor beneath the bathroom, leaving the particleboard flooring and the timbers around it stained, with fungal growth starting on the surfaces. Because the bathroom is being rebuilt, the owner needed the subfloor made safe now, without paying to replace materials that the rebuild will open up anyway. This post covers what we found, what a make-safe involves, why we encapsulated, and what it cost.
The Job
The home is in Hazelbrook in the Blue Mountains, where cool, damp winters and closed-in subfloors make mould under the house a common problem. We visited several times in May and June 2026 to assess the subfloor and prepare the quote, and carried out the work in mid-June.
Assess the subfloor beneath the bathroom
Clean the surface fungal growth on the subfloor timbers and flooring
Encapsulate the cleaned surfaces
Leave the subfloor controlled and ready for the bathroom rebuild
What We Found Under the Bathroom
Directly under the bathroom plumbing, the underside of the particleboard flooring had a large brown water stain spreading out from where the pipes come through the floor, and the timber beside it was darkened.
Further along, the flooring and timber next to the fibre cement wall sheeting showed the same staining, along with dark marks on the timber framing.
Staining like this shows the flooring has been wet repeatedly over a long period, which is what a failed shower membrane does: each shower sends a little more water through to the subfloor. Once particleboard and timber stay damp, fungal growth follows, and a closed-in subfloor gives it little chance to dry out.
During our May assessment visit we also found white surface fungal growth spreading across the timber under the floor. This is the growth we cleaned off during the make-safe.
Where the bathroom pipes pass down through the floor, the timber around them was dark and stained.
What a Mould Make-Safe Involves
A make-safe controls the mould now, without doing the full repair that will happen later. Here, the bathroom rebuild will open up the floor anyway, so replacing flooring now would mean doing the work twice. Instead we:
Cleaned the surface fungal growth from the subfloor timbers and the underside of the flooring
Encapsulated the cleaned surfaces with a coating that seals in remaining residue and helps stop spores being released
Left the subfloor in a controlled state until the builder starts
Why Encapsulation Was the Right Call
Encapsulation is a temporary control measure. It does not stop the shower leak and it is not a substitute for replacing damaged materials. It makes sense when demolition is already planned, as it was here. When the bathroom is rebuilt, the builder can replace the failed waterproofing membrane and the damaged flooring.
We have used the same approach in a bathroom leak make-safe in Blaxland and on a Haberfield job where mouldy material could not be removed.
Outcome and Next Steps
The make-safe took two days. The subfloor is now cleaned and encapsulated, and the owner is waiting for the builder to rebuild the bathroom. The owner has engaged an independent hygienist to carry out the post-remediation verification, so the result is checked by someone with no stake in the job. For the rebuild we recommend:
Installing a new shower waterproofing membrane and having it checked before tiling
Replacing the damaged particleboard flooring
Improving subfloor ventilation if the space stays damp
Post-remediation verification (PRV) by an independent hygienist, which the owner has already arranged
Standards We Follow
Our mould work follows the ANSI/IICRC S520 standard for professional mould remediation, and water damage work follows the IICRC S500 standard. AAA Mould Removal is an IICRC Certified Firm.
What It Costs
This subfloor make-safe took two days and cost $4,500 + GST. Every job is different: the cost depends on how much area is affected and what needs to be removed. Our mould inspection and quote are free, and professional mould and moisture reports start from $500 + GST. See our mould removal price guide.
If you are in the Blue Mountains, see our Blue Mountains mould removal page, or call 1300 739 783 to book a free inspection.
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
AAA Mould Removal is an IICRC Certified Firm. Michael is also completing a double degree in Medical Science and Environmental Science at Macquarie University.
Worried About Mould or Water Damage?
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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