Leaks
How to tell if your shower is leaking
6 min read
Short answer
A leaking shower usually shows up outside the bathroom before it shows up inside it: swelling skirting boards, lifting floor coverings, a musty smell, or a stain on the ceiling below. Damp that appears after the shower is used and dries out slowly between uses points to water escaping the wet area rather than to condensation.
Showers rarely fail all at once. Water finds a path through a hairline crack in grout or a split in silicone, soaks into the bed beneath the tiles, and travels until it reaches something that shows. By the time a mark appears on a wall, the water has usually been moving for a while.
That delay is why the first signs turn up in the next room rather than in the shower itself, and it is why a shower can look perfectly sound and still be leaking.
Signs inside the bathroom
- Grout that is dark, crumbling, powdery or missing in patches, particularly in the corners and along the floor-to-wall junction.
- Silicone that has lifted, split, gone brittle, or grown black staining that does not clean off.
- Tiles that sound hollow when tapped, which can mean the bed beneath has lost its bond.
- A floor waste that drains slowly, or water that sits on the floor instead of running to the drain.
- Efflorescence: a white, chalky deposit at the edges of tiles or along grout lines, left behind as water passes through and evaporates.
Signs outside the bathroom
These are the ones people usually notice first, and they matter because they tell you water has already left the wet area.
- Skirting boards next to the bathroom that are swelling, cupping or lifting away from the wall.
- Carpet, floating floor or vinyl that feels damp, lifts at the edge, or discolours along the wall the shower backs onto.
- Paint bubbling or a stain spreading on the other side of the shower wall.
- A stain on the ceiling below an upstairs bathroom, often ring-shaped and darker at the edge.
- A persistent musty smell in a hallway or robe that shares a wall with the bathroom.
How to tell a leak from condensation
Condensation forms on cold surfaces during and just after a shower, and it clears once the room ventilates. It sits on the surface, it is fairly even across a wall or window, and it improves markedly if you run an exhaust fan or open a window.
A leak behaves differently. It appears in one place rather than across a whole surface, it gets worse with use rather than with humidity, and it dries slowly or never fully dries. Damp that is still there two days after the shower was last used is not condensation.
A simple test: stop using the shower for two or three days and use another bathroom if you have one. If the damp area starts to dry out and then returns once the shower is back in use, the shower is the source.
How to tell a leak from a plumbing fault
Not every wet patch near a bathroom is a wet-area failure. A leaking pipe in the wall, a failed tap body, a perished flexible hose under a vanity or a blocked waste can all produce similar-looking damage, and none of them is fixed by regrouting.
The rough distinction is use. Damage from a shower leak tracks with showering. Damage from a supply pipe often continues regardless, because the pipe is under pressure whether or not anyone is home. Damage that is worse after a bath or after the washing machine runs points somewhere else again.
This distinction decides who you should call. If the evidence points at pipework, a licensed plumber is the right trade, and we will tell you so rather than sell you a repair that will not fix it.
What is actually failing
In a tiled shower, the waterproof membrane sits under the tiles, not on them. The tiles, grout and silicone are the first barrier; the membrane is the second. Grout is cement-based and porous by nature, and silicone is a wearing part that has a service life, so a small amount of water reaching the bed is expected and the membrane is what is supposed to deal with it.
Problems start when the surface lets through more than the membrane was designed to handle, or when the membrane itself is defective, was never installed correctly, or was compromised later by something like a fixing screwed through it.
AS 3740, the Australian Standard for waterproofing of domestic wet areas, sets out where waterproofing is required and how high it has to go. Showers built before it applied, or built without it being followed, are the ones that tend to fail earliest.
What to do next
Photograph what you can see, including the area outside the bathroom, and note when it appeared and whether it changes with use. That history is genuinely useful for diagnosis and it costs nothing to record.
Then get it looked at. A shower leak does not improve on its own, and the difference between a surface repair and a rebuild is usually how long the water has been moving.
In short
- The first signs of a shower leak usually appear outside the bathroom, not inside it.
- Damp that persists between uses is a leak. Damp that clears with ventilation is condensation.
- Damage that continues while nobody is using the shower points at pipework, not the wet area.
- The tiles are the first barrier. The waterproof membrane underneath is the one that matters.
Common questions
- How long can a shower leak before it causes damage?
- There is no fixed period. Damage depends on how much water is escaping, what is underneath, and whether the structure can dry out between uses. A slow leak over a timber floor can cause more harm than a faster one over concrete, because the water has something to rot.
- Can a shower leak without any visible cracks?
- Yes. Grout can be porous or debonded without looking cracked, silicone can fail behind the visible face, and a defective membrane produces no surface sign at all. A shower that looks sound can still leak.
- Does a leaking shower always mean the waterproofing has failed?
- No. Many leaks are caused by defects at the tiled surface, such as deteriorated grout, perished silicone or an unsealed junction, and the membrane beneath is intact. Which of the two it is can only be established by inspection.
Related service: Bathroom Leak Repair