Signs your shower is leaking
A shower membrane lasts 10 to 15 years. How to tell a failed one from a grout problem, and what the damage looks like from the other side of the wall.
A leaking shower rarely announces itself inside the shower. The tiles look fine, the grout looks tired, and the evidence turns up somewhere else: a skirting board lifting in the hallway, a musty smell in the linen cupboard that backs onto the wet wall, or a patch of carpet by the doorway that never quite dries. By the time water is visible, it has usually been moving through the wall cavity or across the bearers for months. A membrane has a working life of roughly 10 to 15 years before it gives up, and leaks are present in something like 55 to 65 per cent of showers across the country, so on a house of a certain age this is closer to a maintenance milestone than bad luck.
What do the warning signs mean?
| What you see | Most likely cause | What it means for the repair |
|---|---|---|
| Dark or lifting skirting on the other side of the shower wall | Water in the wall cavity, membrane failed at the base to wall junction | Rebuild, not a surface repair |
| Carpet or floorboards damp at the bathroom doorway | Water tracking under the floor tiles toward the door | Rebuild, floor waterproofing has failed |
| Paint bubbling or a stain on the ceiling of the room below | An upper level shower leaking through the floor, common in two storey Cranbourne North and Cranbourne East houses | Rebuild, and repair of the ceiling below |
| Efflorescence, a chalky white deposit at the base of the tiles | Water sitting in the bed and wicking out through the grout | Rebuild |
| Grout missing or crumbling only in the internal corners and along the base | Movement, not water entry yet | Correct the joints, and check whether it has happened before |
| Loose or drummy tiles when tapped | The bed is saturated or has lost its bond | Rebuild |
| Mould that returns within a fortnight of cleaning | Trapped moisture behind the surface, or an exhaust fan that is not moving enough air | Investigate before deciding |
| Water pooling in the middle of the floor rather than draining | Falls laid wrong or the screed has moved | Rebuild, the falls are in the screed under the tiles |
| Water meter ticking over with every tap off | A pressurised pipe leak rather than a shower leak | Plumber, this is a different problem |
Is it a grout problem or a membrane failure?
These two get confused constantly, and the difference decides whether you spend a few hundred dollars or several thousand.
Grout is not waterproof. It never was. Grout is a joint filler, and water passing through it is normal and expected. The membrane underneath is the thing that stops water reaching the frame and the floor. So a shower with tidy grout can be soaking the wall cavity, and a shower with ugly grout can be perfectly watertight.
The useful distinction is where the problem sits and whether it repeats:
- Grout alone. Grout has worn or discoloured evenly across the flat faces of the tiles, the corners are still sound, there is no damage outside the room, and this has not happened before. Regrouting the flat joints is reasonable maintenance.
- Movement. Grout is cracking specifically in the internal corners, along the floor to wall junction and around the hob. Those locations should never have carried rigid grout in the first place. If the last tradesperson simply refilled them, they will open again on the next seasonal cycle.
- Membrane failure. There is damage on the far side of the wall or under the floor, tiles are drummy, efflorescence is present, or the shower has already been regrouted more than once. At that point the water is past the tiles and the repair is the wet area, not the joint.
Why this happens more in parts of Cranbourne
Shrink and swell clay left behind by the drained Koo Wee Rup swamp runs under the old township and the western half of the postcode. Those soils take up water through winter and give it back through summer. The slab and the wall frame ride that movement, and the movement is passed straight into anything rigid sitting on top of them. A grout line is rigid. A correctly detailed silicone joint is not. That is why so many houses here carry a regrout history, each attempt lasting a season or two before splitting in exactly the same place.
Age clusters matter as well. Cranbourne West filled in through the 1990s, so those sand and cement shower bases are 28 to 35 years old and well past the point where a membrane can be relied on. Cranbourne North, led by Camden Green from 2003, is around the 20 year mark and entering the same window now. Cranbourne East is newer, and the problems there tend to be an acrylic base that flexes, a framed screen leaking at the track, and an exhaust fan too small for the room, rather than a failed membrane.
What can you check yourself?
- Isolate the water source. Run only the shower head for ten minutes with the floor waste and the rest of the room dry, then check the far side of the wall. Do it again with the head off and water running from the mixer to the floor only. If the damage tracks with the second test, the leak is at the floor and the base to wall junction rather than higher up the wall.
- Check the waste. Block the floor waste with a rubber stopper, let a couple of centimetres of water stand in the shower base for an hour, and watch the level. A dropping level with nothing draining points to the base or the waste connection.
Neither test proves the membrane is intact. They narrow down where to look, which is worth doing before anyone starts cutting tiles.
Why is a regrout not a repair?
Regrouting replaces the filler between the tiles. It does nothing to the membrane, the screed, the falls or the bed, because those are all underneath. Where the membrane has failed, a regrout seals the surface just well enough to hide the symptom for a few months while the frame behind keeps getting wet. The second and third regrouts are the ones that cost real money, because each buys a little time at the price of more damage.
A rebuild strips the tiles, the bed and the screed, checks the frame and the sheeting for rot, reforms the falls, lays a new membrane and takes it up the wall to the height the Code sets, then puts purpose made movement joints where the movement actually is. The standard and that height are on what the law requires, and the work itself is described on shower rebuilds and waterproofing.
When the whole room is the better job
Where the shower has failed in a bathroom that is otherwise original, rebuilding only the shower leaves new work joined to twenty or thirty year old tiling, and matching tiles from that era is usually impossible. On a house at that age the sensible comparison is the shower rebuild against a full renovation, which is set out band by band on bathroom renovation cost in Cranbourne. Either way the room is out of use while it happens, and the sequence is on how long a bathroom renovation takes.
Send photos of the shower and of the damage on the other side of the wall through the quote form, along with the age of the house, and you get a written assessment of which of the two it is.