Why this stage decides whether the room lasts
Every other part of a bathroom can be repaired on its own. A cracked tile gets replaced. A leaking tap gets rewashered. A swollen vanity gets swapped.
Waterproofing is different. It sits underneath the screed and the tiles, so a failure cannot be reached without dismantling the finished room above it.
That asymmetry is the entire argument for not compressing this stage. Doing it properly costs a few hundred dollars of material and a few days of program. Doing it badly costs the room.
What actually gets waterproofed
Membrane is not applied to the whole room in every case. AS 3740 sets out what has to be protected and the extent depends on the fixtures and the construction. Broadly:
- The shower floor and the walls around it, to a height set by the standard and the shower type
- The whole bathroom floor, in most modern construction and particularly on timber floors
- 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 — because every hole is a potential path
Junctions and penetrations are where failures overwhelmingly start. A membrane rolled beautifully across a flat floor and then rushed at the corner is a membrane that fails at the corner.
How failures show up in post-war houses
This is where the local construction matters. Most of the housing across Bankstown, Yagoona, Condell Park and Greenacre sits on suspended timber floors, and that changes where the water goes.
In a slab building, a failed membrane usually announces itself in the unit below as a ceiling stain — obvious, and someone else's ceiling. On a suspended timber floor, water moves into the floor frame instead, where nobody sees it.
The tells are subtler and slower: springiness underfoot near the shower, swollen skirting in the adjoining room, a musty smell in the subfloor, or a patch of floor that feels different. Damage can run for years before anything visible appears, and by then the framing is usually involved.
That is why, on a strip-out of an original bathroom here, the framing behind the shower is one of the first things worth looking at properly.
Cure time is not padding
The membrane goes on in coats. Each coat needs to dry. When the last is on, the system needs to cure before screed and tiles cover it. In practice that puts several days of unavoidable waiting in the middle of a bathroom program, and longer in cold or humid weather.
It is the stage most often squeezed when a job is running late, and the worst possible place to find the time. If a builder offers to make up a week, ask specifically 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
- Cure time, shown in the program as its own line
- The documentation on completion
What you should get at handover
The certificate or compliance documentation, the product used, and the date. Keep it with your property records.
Photographs are the other thing worth having. A handful of pictures of the completed membrane before the screed covers it costs nothing, and it is the only record that will ever exist of what is under your floor. Any contractor confident in the work will take them without being asked twice.
Where this sits
Waterproofing follows screeding and precedes tiling, stage four of five in a full renovation. It applies equally in an ensuite, a small bathroom and a laundry, with the extent varying by room.
Call 02 4404 0504 or send the details through.
The rest of what we do
| Bathroom Renovations | Full bathroom renovations — strip-out, rough-in, waterproofing, tiling and fit-off managed as one job. |
| Ensuite & Powder Room | Ensuites and powder rooms, where every millimetre counts and the set-out has to work around an existing bedroom or hallway. |
| Small Bathroom Renovations | Compact bathrooms where the win is removing what was making the room feel smaller than it is. |
| Laundry Renovations | Laundries renovated on their own or alongside the bathroom, which is almost always the cheaper way to do both. |
| Bathroom Tiling | Floor and wall tiling, falls to waste, niches and set-outs — the finish most people actually judge the room on. |
| Vanities & Cabinetry | Vanities, mirror cabinets and storage sized to the room rather than to whatever the showroom had in stock. |
Questions people ask before they commit
What standard applies to bathroom waterproofing?
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 your contractor to confirm in writing that the work is to AS 3740.
How long does the membrane take to cure?
The membrane goes on in coats with drying time between them, then needs a further cure before tiling — commonly a few days in total and longer in cold or humid weather. That is chemistry, not padding. A program showing no gap between waterproofing and tiling has not allowed for it.
How do I know if the old waterproofing has failed?
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, swollen skirting in the next room, or a stain on a ceiling below. By the time any of those appear, water has usually been moving for a while.
Can it be repaired without removing the tiles?
Rarely. The membrane sits under the screed and tiles, so reaching it means removing them. Surface-applied products marketed as repairs can buy time on a minor issue but do not replace a failed membrane. Anyone offering to fix a genuine membrane failure without lifting tiles is selling a delay.
Is the waterproofer separately licensed?
Waterproofing of wet areas is licensed work in NSW with specific licence categories. Ask who is applying the membrane and what licence they hold, and get the certificate or documentation on completion. Keep it — it matters if you sell and it matters much more if there is ever a claim.