Leaking showers and bathroom waterproofing: signs, causes and fixes
A leaking shower usually shows up outside the shower first: swollen skirting, door frames or vanity panels, loose or hollow-sounding tiles, crumbling grout, mould or stains in the next room, or a stain on the ceiling below. The cause is typically a failed or missing waterproofing membrane under the tiles, failed seals at junctions, or a plumbing leak. Australia’s first wet-area waterproofing standard, AS 3740, was published in 1989, so original bathrooms older than that rely on older methods. Regrouting and resealing maintains a sound shower; a failed membrane needs the tiles removed and the waterproofing redone.
- 01SurfaceTiles, grout and silicone shed most of the water
- 02MembraneThe layer underneath stops what gets through
- 03FallThe floor slopes so water reaches the drain, not the walls
Damage outside the shower is how a failed membrane usually shows itself.
Tiles are not the waterproofing
Tiles and grout shed most water, but grout is porous and water reaches the bed behind them. The real waterproofing is a membrane under the tiles, turned up at walls and sealed around the waste and any penetrations, with the floor falling to the drain. When that membrane is missing, damaged or poorly terminated, water escapes into the wall framing, floor structure and neighbouring rooms, often for months before anything shows. Victoria's Building and Plumbing Commission notes that compliant waterproofing is required under AS 3740 or the ABCB Housing Provisions.
Signs of a leaking shower
| Sign | Often means | Check next |
|---|---|---|
| Swollen or stained skirting, door frame or vanity near the shower | Water escaping sideways through the wall or floor | Moisture readings along the wall; whether it worsens after showers |
| Loose, cracked or hollow-sounding tiles | Water behind the tiles has weakened the bed or adhesive | The extent of drummy tiles, and the membrane underneath |
| Crumbling or missing grout, failed silicone at corners and the base | An entry point for water; may be the start of a bigger problem | Whether staining appears beyond the shower |
| Mould or stains on the other side of the shower wall | Long-term leakage into the wall | Framing condition, and whether it is a plumbing leak |
| Stain on the ceiling below an upstairs bathroom | A leaking floor membrane, waste or pipe | Whether it follows shower use or is constant |
| White powdery deposits on tiles or grout | Moisture moving through the bed and leaving salts behind | Membrane condition and fall to the drain |
| Musty smell that persists after airing | Moisture trapped in the structure | Hidden areas such as cupboards backing onto the bathroom |
QBCC's maintenance guide suggests checking the silicone at the base of the shower and where screens meet walls, and looking inside cupboards and behind fittings on walls that back onto wet areas for signs of water seeping through.
Waterproofing or plumbing?
A simple pattern helps. If staining appears or grows after the shower is used and stays dry otherwise, suspect the shower floor, walls or seals. If it is wet regardless of use, suspect a supply pipe under pressure, and call a plumber promptly. An unexplained increase in your water bill points the same way. A plumber can pressure-test the pipes, and a leak detection specialist can help separate the two.
How the age of the bathroom changes the question
| When the bathroom was built | What to expect | What to ask |
|---|---|---|
| Before 1989 | Built before the first national wet-area standard (AS 3740), using older methods that are now well past their likely life | When was it last renovated? Original showers of this age are a common leak source |
| 1989 to the 2000s | Built to an early edition of AS 3740; workmanship varied widely | Is there a waterproofing certificate? Who did the work? |
| From 2012 onward | The NCC set out where waterproofing is required, with AS 3740 as the technical solution | Ask for the waterproofing certificate and the membrane product used |
| From NCC 2022 | The ABCB Housing Provisions offer detailed wet-area construction as an alternative to AS 3740 | Same: a certificate, the product and the installer |
The bathroom’s date matters more than the house’s. A 1950s house can have a 2018 bathroom, and a 1990s house can still have its original shower. See the dated milestones table for how this fits with other changes.
From regrouting to a full strip-out
| Option | What it does | When it suits |
|---|---|---|
| Regrout and reseal | Replaces failed grout and silicone at the surface | Routine maintenance where the membrane is sound and no water is escaping |
| Surface sealers and grout-injection products | Attempts to seal the tiled surface from above | Sometimes a short-term measure; does not replace a failed membrane, so ask what warranty and evidence support it |
| Partial strip-out | Removes tiles in one area, such as the shower floor, to renew the membrane there | A defined, localised failure with sound surroundings |
| Full strip-out and re-waterproofing | Removes tiles and bed, renews the membrane and retiles | A failed or missing membrane, widespread drummy tiles, or water damage to framing |
Whatever the scope, ask for the membrane product, the installer’s licence and a waterproofing certificate, and photographs of the membrane before tiling. Those records are what a buyer, insurer or future owner will ask for, as covered in keeping a record of your home.
In an apartment, a leak is a neighbour issue
In strata buildings, a failed shower can damage the lot below and common property. Who is responsible for the membrane and the repair depends on your state, the by-laws and where the failure is. Report it early, keep photographs, and use the owners corporation process; see strata risks for owners.
Common misreads
| What people say | What is closer to right |
|---|---|
| "The tiles are fine, so the shower is fine" | Tiles can look perfect over a failed membrane. Check the walls, skirting and rooms around it. |
| "Regrouting will fix the leak" | Only if the leak is at the surface. It will not fix a failed or missing membrane. |
| "Mould in the bathroom means a leak" | Often it is condensation from poor ventilation. Leaks show as damage outside the shower. |
| "It is a new bathroom, so it is waterproofed" | Ask for the certificate. Workmanship varies, and some renovations skip proper membranes. |
Worked example: a swollen door frame next to the ensuite
Illustrative reasoning example, not an inspected property. A 1990s house has an original ensuite. The bedroom door frame beside it has swollen at the base, and the shower grout was replaced a year ago. The tiles look sound.
The new grout and the swelling together suggest water is escaping below the surface. The next step is moisture readings along the wall and skirting, then a plumber to rule out the supply pipes. If the pipes test sound and the moisture follows shower use, the likely scope is the shower floor membrane. Get a defined quote for that area, with a certificate on completion, rather than another regrout.
Frequently asked questions
How do I know if my shower is leaking?
Look outside the shower: swollen or stained skirting, door frames or vanities, loose or hollow tiles, crumbling grout, mould on the other side of the wall, or a stain on the ceiling below. Damage that appears after showers points to the shower; damage that is constant points to a pipe.
When did bathroom waterproofing become a standard in Australia?
The first Australian Standard for waterproofing residential wet areas, AS 3740, was published in 1989 and revised in 1994. Original bathrooms from before then rely on older methods.
Will regrouting stop a shower leak?
Only if the problem is at the surface. Regrouting and resealing maintain a sound shower, but they will not fix a failed or missing waterproofing membrane under the tiles.
Do grout sealers or injection products fix leaking showers?
Sometimes as a short-term measure, but they do not replace a failed membrane. Ask what evidence and warranty support the product before relying on it.
What documents should I ask for after a bathroom renovation?
A waterproofing certificate, the membrane product used, the installer’s licence details and photographs of the membrane before tiling.
Is bathroom mould a sign of a leak?
Not always. Mould on ceilings and corners is often condensation from poor ventilation. Leaks tend to show as damage outside the shower area, such as swollen skirting or stains in adjacent rooms.
Who pays for a leaking shower in an apartment?
It depends on the state, the by-laws and where the failure is. Report it to the owners corporation early with photographs and follow the scheme’s process.
How this guide was researched
We separate surface seals, the membrane and plumbing as distinct water paths, date the bathroom rather than the house, and order repair options from least to most invasive, with a fictional example.
Limits: A membrane cannot be inspected without removing tiles. Moisture readings and leak testing narrow the cause; strata responsibility depends on state law and by-laws.
Sources
- Waterproofing of wet areasBuilding and Plumbing Commission (formerly the Victorian Building Authority) · accessed
- AS 3740-1994 Waterproofing of wet areas within residential buildingsStandards Australia · accessed
- NCC 2022 seminars: health and amenity (wet areas)Australian Building Codes Board · accessed
- Your essential home maintenance guideQueensland Building and Construction Commission · accessed
- MouldNSW Health · accessed