Bathroom waterproofing Geelong is the part of a bathroom nobody sees and everybody relies on. It sits under the tiles, does its job silently for decades, and only ever announces itself when it's failed — by which point the fix means tearing the room out. It's also the single most common corner cut on a cheap job. So it's worth understanding what the standard actually requires, and how to know yours was done properly.
What AS 3740 is, and why it exists
AS 3740 is the Australian Standard for waterproofing domestic wet areas. It's mandatory under the National Construction Code, it must be done by a licensed installer before any tiling, and it should come with a compliance certificate you keep on file. It's the one part of a bathroom you never let anyone rush or skip.
The standard exists because water is relentless and bathrooms are unforgiving. Get the membrane right and the room lasts twenty years without a thought. Get it wrong — a missed corner, a poorly sealed penetration, the wrong fall to the waste — and water tracks into wall cavities, subfloors and adjoining rooms, causing rot, mould and structural damage that's far more expensive than the waterproofing ever was. The current version is AS 3740:2021.
What the standard actually requires
You don't need to memorise the standard, but knowing roughly what it covers helps you tell a thorough job from a rushed one.
| Area | Requirement in plain terms |
|---|---|
| Shower floor | Fully waterproofed, with correct falls to the floor waste |
| Shower walls | Membrane to a defined height around the wet zone |
| Bathroom floor | Waterproofed where required, especially in fully enclosed or timber-floor situations |
| Penetrations | Taps, wastes and pipes sealed where they pass through the membrane |
| Hobs & junctions | Wall-to-floor junctions and hobs detailed and sealed |
What changed in the 2021 update
AS 3740 was updated in 2021, refining detail around membranes, penetrations and wet-area definitions rather than reinventing the approach. The practical takeaway for a homeowner is simple: your bathroom should be waterproofed to the current 2021 version, by someone who works to it every week. If a quote is vague about the standard, that's worth a question.
The compliance certificate — what it is and why you keep it
When waterproofing is done properly, you should receive a compliance certificate stating the work meets AS 3740. This isn't paperwork for its own sake. If a leak ever becomes an insurance claim, your insurer may ask for it — and without it, a claim can be refused. It's also evidence for a future buyer that the wet areas were done to standard. File it with your other renovation documents and don't lose it. We provide certification as standard on our waterproofing service.
Why waterproofing fails — and what it costs to fix
In Geelong's older housing, failed waterproofing is one of the most common things we uncover at demolition. In pre-1990 homes, the original membrane has often broken down, was never installed to today's standard, or was compromised by movement over the decades — a pattern we see regularly on bathroom waterproofing Grovedale jobs and similar established suburbs. By the time it shows up as a musty smell, lifting tiles or a damp patch on the other side of the wall, the damage is done.
The cruel part is the cost asymmetry. Waterproofing is only around 5–10% of a bathroom budget to do right the first time. Fixing failed waterproofing after tiling means removing the tiles, re-doing the membrane and re-tiling — multiples of the original cost. There's no patch; it's a redo. That's exactly why it's the wrong place to save money, and why we check it first on any older bathroom.
Signs your waterproofing may have failed
- A persistent musty or damp smell in or near the bathroom
- Tiles lifting, drumminess underfoot, or cracking grout
- Damp patches or paint bubbling on adjoining walls or ceilings below
- Mould that keeps returning no matter how often you clean it
- Movement or spongy feel in the floor
How to know your waterproofing was done right
You can't see the membrane once the tiles are on, so the assurance comes from the process, not the finish. Insist on three things: the work is done to AS 3740 by a licensed installer, it goes down before any tiling (and is given time to cure), and you receive a compliance certificate at the end. A good builder does all three without being asked — it's standard practice on every job we complete. This matters even more in a walk-in shower, where there's no screen containing the water. It ties directly into the bathroom tiling Geelong that follows — tiling over compliant waterproofing is what makes a bathroom last.
Frequently asked questions
Is waterproofing a legal requirement in a bathroom?
Yes. Waterproofing of domestic wet areas is mandatory under the National Construction Code and must meet Australian Standard AS 3740. In a bathroom, the shower, the floor and the walls around wet zones all have defined waterproofing requirements, and the work must be done before any tiling.
What is AS 3740?
AS 3740 is the Australian Standard for waterproofing of domestic wet areas — bathrooms, ensuites, laundries and the like. It sets out where waterproofing membranes are required, how high they must go, how falls and floor wastes work, and how penetrations are sealed. The current version is AS 3740:2021.
Do I need a certificate for bathroom waterproofing?
You should always get a waterproofing compliance certificate confirming the work meets AS 3740. Keep it on file — your insurer may ask for it if a water-damage claim is ever made, and it's proof the work was done to standard if you sell the home.
How long does bathroom waterproofing last?
A properly installed membrane to AS 3740 should last the life of the bathroom — 15 to 20 years or more. Failures usually come from poor installation, skipped detailing at penetrations, or movement in the substrate, not from the membrane simply wearing out. That's why who installs it matters.
Who can legally do waterproofing in Victoria?
In Victoria, wet-area waterproofing must be carried out by a suitably licensed or registered practitioner, and in most cases the waterproofer or tiler holds the relevant waterproofing competency. Ask your builder who does it and confirm you'll receive a compliance certificate for the work.
Why Work With a Local Bathroom Renovation Team
Choosing who does the work matters as much as any design decision. Here's what a local, in-house team brings to a bathroom renovation:
- Complete renovation management — one point of contact from quote to completion, rather than juggling separate trades yourself.
- Trade coordination — plumbing, electrical, waterproofing and tiling scheduled in the right order, on time.
- In-house tiling and waterproofing expertise — the two trades that matter most to a bathroom's long-term performance.
- Written, itemised quotes — a clear scope before any work begins, not a vague allowance.
- Local Geelong experience — familiarity with the mix of older and newer housing stock across the region and what each typically needs.
Recent Bathroom Renovation Projects
We've completed bathroom renovations across a range of Geelong homes, from straightforward refreshes to full reconfigurations. You can see examples of completed work, including bathrooms, on our projects page.
Waterproofing done right, and certified
Our Bathroom Renovation Specialists Geelong team completes all wet-area waterproofing to AS 3740 with a compliance certificate, before any tiling begins — on every bathroom we build. Get a quote from a licensed local team.
Get a free quoteThis guide is part of our complete bathroom renovations in Geelong series. See how waterproofing fits the wider budget in our bathroom renovation cost guide, or explore our waterproofing service and recent projects.