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What are the signs of a shower leak?

The short answer

Damp or bubbling paint on the other side of a shower wall, drummy tiles, a musty smell that cleaning does not fix, and lifting floorboards nearby. All point to water escaping the wet area.

TradieAnswers editorial · written in-house and sourced to the authorities listed below

Checked against 4 published sources, listed in full at the end of this page. How we source this

Shower leaks are slow, hidden and expensive, and by the time they are obvious the damage is usually in the structure rather than the bathroom. Knowing the early signs is worth a great deal.

The signs, roughly in order of appearance

  1. A musty smell in or near the bathroom that cleaning does not resolve.
  2. Paint bubbling, staining or peeling on the other side of a shower wall.
  3. Skirting boards or architraves near the bathroom swelling or lifting.
  4. Tiles sounding hollow when tapped, particularly near the floor waste and in the corners.
  5. White crystalline deposit at grout lines or on the wall outside, which is efflorescence and means water is moving through the substrate.
  6. Timber floors cupping or lifting in an adjoining room.
  7. A stain on the ceiling below an upstairs bathroom, which is the late stage.

What is usually behind it

  • Failed waterproof membrane, particularly at junctions and penetrations rather than in the middle of a wall.
  • Cracked or missing grout and perished silicone at the wall to floor junction.
  • Inadequate fall to the floor waste, leaving water sitting.
  • A failed or poorly installed shower screen seal.
  • Movement in the substrate cracking the membrane.

Left alone, a shower leak moves from a bathroom problem to a structural one: rotted framing, damaged subfloor and, in the worst cases, termite attraction. It is one of the few maintenance items where waiting reliably multiplies the cost.

Who does this work

You may need a waterproofing specialist

Because resealing a joint is a homeowner job, but a failed membrane sits under the tiles and cannot be repaired without lifting them.

Depending on the cause it can also involve plumber or tiler.

This work is licensed, though the threshold and the licence class differ between states. Check a licence in your state

Sources

Every source below was fetched and its response recorded on the date shown. Where a government site blocks automated clients, that is noted rather than reported as a successful check.

  1. National Construction Code · Australian Building Codes BoardChecked 2026-08-10 · responded 200 OK
  2. Standards Australia · Standards AustraliaChecked 2026-08-10 · responded 200 OK
  3. Building and renovating · Consumer Affairs VictoriaChecked 2026-08-10 · responded 200 OK
  4. Australian Building Codes Board · Australian Building Codes BoardChecked 2026-08-10 · responded 200 OK

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