All advice / Planning and cost
Mould is a symptom, not the problem
Mould grows where moisture sits. In a bathroom, that means grout lines, silicone joints, ceiling corners and behind tiles where water has worked its way in. Cleaning removes the visible growth, but if the conditions stay the same, it comes back.
The real problems are usually poor ventilation, failed waterproofing, or materials that trap moisture instead of shedding it. A renovation is the chance to fix all three at once.
Poor ventilation is the number one cause
Steam from a hot shower fills the room in minutes. If the bathroom has no exhaust fan, a weak fan, or a fan that vents into the roof cavity instead of outside, that moisture settles on every surface. It soaks into grout, collects in corners and feeds mould growth.
A properly sized exhaust fan that vents to the outside — not into the roof space — clears steam before it settles. A timer or humidity sensor keeps the fan running after you leave the room, which is when most of the drying happens.
Our ventilation guide covers fan sizing, ducting and the common mistakes that make ventilation fail.
Failed waterproofing lets water behind the tiles
Waterproofing is a membrane applied to the walls and floor before tiling. When it is intact, water stays on the surface. When it fails — through age, movement, or poor application — water gets behind the tiles and into the wall framing.
Behind the tiles, there is no airflow. Moisture sits there permanently. Over months and years, it rots timber framing, degrades plaster and creates a mould colony that is invisible from the outside. The first sign is often a musty smell or discolouration at the base of the wall.
In a renovation, the old tiles and lining come off, the framing is inspected and repaired, and new waterproofing is applied to AS 3740 — the Australian standard for wet-area waterproofing. A compliance certificate confirms the work.
Material choices that resist mould
Cement-based grout absorbs moisture. Epoxy grout does not. In a shower recess, epoxy grout resists staining and mould growth far better than standard grout. It costs a little more and takes longer to apply, but it lasts longer and stays cleaner.
Large-format tiles reduce the total length of grout joints. A wall covered in 600 by 1,200 tiles has far less grout than the same wall in 100 by 100 mosaics. Less grout means less surface for mould to colonise. Our large-format tiles guide covers the trade-offs.
Moisture-resistant plasterboard (green board) is rated for wet areas and holds up better than standard plasterboard if any moisture does get past the membrane. It is standard practice in a new bathroom build.
Silicone joints and ongoing maintenance
Silicone is used where tile meets a fixture — around the shower base, the bath rim, and where the wall meets the floor. Silicone is flexible, which is why it is used at movement joints, but it is also the first place mould appears because it stays damp.
Anti-mould silicone contains a fungicide that resists growth for several years. Replacing silicone every five to eight years is normal maintenance. It is a 30-minute job for a professional and keeps the bathroom looking and performing well.
How ETR addresses mould at the source
In a renovation, the old surfaces come off. Adam Dawood inspects the framing and substrate for rot, mould damage and waterproofing failure. Damaged framing is replaced. New waterproofing goes on to AS 3740 with a compliance certificate.
The design includes proper mechanical ventilation, material choices that resist moisture, and grout and silicone specified for wet areas. The result is a bathroom that stays dry, not one that needs constant cleaning to keep mould at bay. A free on-site measure anywhere in Sydney is the starting point.
Frequently asked questions
Can I just clean the mould instead of renovating?
You can clean the visible growth, but if the cause is poor ventilation or failed waterproofing, it will come back. Cleaning treats the symptom. A renovation treats the cause — proper ventilation, new waterproofing and materials that resist moisture.
Is bathroom mould dangerous?
It can be. Some mould species release spores that irritate airways and trigger allergic reactions, especially in children, older adults and people with asthma. Mould hidden behind walls can grow for years without being seen.
How do I know if the waterproofing has failed?
Common signs are discolouration or swelling at the base of tiled walls, a musty smell, soft or spongy patches in the wall, or mould that keeps returning despite cleaning. Water damage to the ceiling of the room below is another indicator.
Does ventilation alone stop mould?
Ventilation removes airborne moisture and is the single biggest factor. But it does not fix water getting behind tiles through failed waterproofing. Both need to be right. A renovation addresses both at once.
What is the difference between epoxy and cement grout?
Cement grout absorbs moisture and is porous. Epoxy grout is non-porous, water-resistant and far more resistant to mould and staining. Epoxy costs more and takes longer to apply, but it performs better in wet areas over time.