The stage that explains why your house is fine
Older housing produces the horror stories — framing that has been absorbing shower water for decades, floors that give underfoot, ceilings stained in the room below. Hills houses largely do not, and the reason is that they were built when waterproofing wet areas to a proper standard was normal practice rather than optional.
So the good news first: on a 1990s or 2000s bathroom, the membrane has almost certainly done its job.
The less convenient news: it still gets replaced. The membrane sits underneath the screed and the tiles. Once those come up in a full renovation, there is no practical way to leave it intact, and no reason to try — a twenty-year-old membrane under new tiles is a false economy with a twenty-year head start.
What gets waterproofed
AS 3740 sets out what has to be protected and the extent depends on the fixtures and the construction. Broadly:
- The shower floor and surrounding walls, to a height set by the standard and the shower type
- The whole bathroom floor, in most modern construction and especially on an upper storey
- Junctions — floor-to-wall and wall-to-wall — with bond breakers so the membrane can move without tearing
- Penetrations — the floor waste, tap bodies, the shower rail
Junctions and penetrations are where failures start. A membrane applied beautifully across a flat floor and rushed at the corner fails at the corner.
Where the walk-in shower changes things
Most Hills renovations here involve replacing a framed corner shower with a fixed panel and running the floor tile continuously into the shower.
That is the right change aesthetically and functionally, and it puts more demand on this stage. Removing the moulded base means the waterproofing and the falls now have to do work that the base used to do. A wider wet area, a continuous floor, no lip at the entry — all of which is entirely achievable and none of which is a place to economise.
If your brief includes a hobless walk-in shower, ask specifically how the fall and the membrane are being detailed at the entry.
Upstairs
Two-storey Hills houses put a bathroom above a living space. The standard does not change but the consequence does — a failure goes into the ceiling below rather than into the ground, where it is both more visible and more expensive.
It is worth being slightly more insistent about documentation on an upstairs room, and worth taking the photographs yourself if nobody offers.
Cure time
The membrane goes on in coats. Each coat dries. The system then cures before screed and tiles cover it. In practice that puts several days of unavoidable waiting into the middle of your program.
It is the stage most often squeezed when a job runs late, and the worst possible place to find the time. If someone offers to make up a week, ask where — and if the answer is here, ask again.
What to ask for in writing
- Confirmation the work is to AS 3740
- Who applies the membrane and what licence they hold
- What is being waterproofed, and to what height
- How the shower entry is detailed if it is hobless
- Cure time, shown in the program as its own line
- The documentation on completion
Waterproofing of wet areas is licensed work in NSW. Ask who is doing it and what licence they hold.
What a failure would actually look like here
Worth knowing the signs even though they are uncommon in this housing, because catching one early is the difference between a repair and a rebuild.
Downstairs, on a slab: damp or bubbling paint on the far side of a shower wall, a musty smell that never clears, drummy or loose tiles at the base of the shower, or swollen skirting in the adjoining room.
Upstairs, on a timber floor: a stain or a sag in the ceiling of the room below, which is the one that gets noticed. Also springiness underfoot near the shower.
In both cases, by the time anything is visible water has usually been moving for a while. The membrane cannot be reached without removing the screed and tiles above it, so there is no minor version of this repair — which is precisely why the stage is worth doing properly rather than quickly.
Surface-applied products marketed as waterproofing repairs can buy time on a minor issue. They do not replace a failed membrane, and anyone offering to fix one without lifting tiles is selling a delay.
Where it sits
After screeding, before tiling — stage four of five in a full renovation. It applies in an ensuite and a laundry too, with the extent varying by room.
Call 02 5944 1412 or send the details through.
The rest of what we do
Questions people ask before they commit
My bathroom was built in 2003 — is the waterproofing still fine?
Very likely it has done its job, which is why Hills bathrooms rarely show the framing damage common in older housing. But it sits under the screed and the tiles, so once those come up in a full renovation there is no way to leave it intact and no reason to want to.
What standard applies?
AS 3740 is the Australian Standard covering waterproofing of domestic wet areas, referenced by the National Construction Code. It sets out where membrane is required, to what height, and how junctions and penetrations are treated. Ask for written confirmation the work is to AS 3740.
How long does it take to cure?
The membrane goes on in coats with drying between them, then cures before tiling — commonly a few days, longer in cold or humid weather. It is chemistry rather than padding, and a program showing no gap between waterproofing and tiling has not accounted for it.
Does an upstairs bathroom need more care?
The standard is the same but the consequence of failure is different. On an upper storey water goes into the ceiling of the room below rather than into the ground. That makes the documentation and the junction detailing worth paying attention to.
What should I get at handover?
The certificate or compliance documentation, the product used and the date, plus photographs of the completed membrane before the screed covers it. Keep all of it with your property records. It is the only evidence that will ever exist of what is under your floor.