WATER DAMAGE TO PLASTER OR SWELLING OF ARCHITRAVES OR SKIRTING BOARDS.

One of the most common signs of a leaking shower is water damage to plaster, architraves, or skirting boards. Showers often leak where the wall tiles meet the shower base or floor tiles. When the grout cracks or silicone breaks down, water seeps through and soaks into the plasterboard or wall sheeting behind the tiles. From there, it can travel along the floor or wall, causing timber frames, architraves, and skirting boards to swell or warp.

You might also notice water stains on walls or ceilings in rooms next to or beneath the bathroom. These are clear warning signs that your shower waterproofing has failed and needs attention before serious damage occurs

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FLOOR OR WALL TILES CRACKING OR LIFTING & FLOORING WARPING

When water leaks beneath floor tiles and soaks into the subfloor, the trapped moisture causes the tiles to loosen and the grout to crack. Without proper waterproofing, the flooring can warp and shift, leading to uneven surfaces, cracked floor grout, and tiles that start lifting or coming away from the floor. In severe cases, water absorption and expansion can create a visible hump or raised section in the bathroom floor.

CRACKED OR MOULDY GROUT AND SILICONE IN YOUR SHOWER

If the grout between the shower wall tiles and shower base tiles is missing, cracked, or constantly mouldy, it’s often a sign of a leaking shower. Many homeowners find that no matter how much they scrub, the mould keeps coming back. This happens because water is penetrating behind the tiles and saturating the wall lining — a clear sign that the shower waterproofing was never installed, or not installed correctly, in line with AS 3740 waterproofing standards.

Silicone can also develop mould that won’t clean off, as the mould grows from behind the surface due to water leaking behind it. In a properly waterproofed shower, this issue does not occur.

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MOULD, MUSHROOMS, OR ANTS AROUND YOUR SHOWER

Some homeowners are surprised to find mushrooms growing near their shower or even in adjoining rooms. This happens because ongoing moisture and decaying subfloor materials create the perfect environment for fungi to thrive. In many cases, the same moisture problem also attracts ants and other pests. Both are clear signs of a leaking shower or failed waterproofing that needs immediate attention.

WHY SHOWER BASES FAIL OR CRACK

Acrylic and polymarble shower bases must be installed on a solid mortar bed with no gaps or hollow pockets. If there are voids beneath the base, it won’t have proper support and will flex under weight, eventually leading to cracks. Since these shower base shells are only around 10mm thick, full support from the mortar bed is essential.

However, even a well-installed base can fail if there are leaks from the wall linings or tiles. Water that seeps underneath the base can soften or break down the mortar bed, causing movement, instability, and premature cracking of the shower base.

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IS THE SHOWER RECESS WALL TILING COMPLETELY FLUSH WITH THE SHOWER BASE?

Shower wall tiles should be installed so they sit flush with the shower base, allowing a neat and continuous bead of silicone to seal the junction between the wall tiles and the base. Tiles should never protrude or overhang the base, as this prevents proper sealing, traps water, and eventually leads to leaks.

A common issue occurs when the shower base has been “checked” into the wall too far or not far enough:

• Checked in too far: The wall tiles protrude and overhang the base, making it impossible to seal properly.
• Not checked in far enough: This creates a flat spot where water can sit against the wall tiles and silicone, eventually seeping through.

In some cases, the shower base is the wrong size for the space, and the builder has “made do” to make it fit. This improper alignment often results in poor sealing, water pooling, and eventual leaks.

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DARK OR DISCOLOURED TILES IN THE SHOWER

If you look at your shower with the door open and notice that the lower wall tiles or floor tiles appear darker than the rest, it’s often a sign of a leaking shower. This happens when water seeps through cracks or gaps and penetrates the wall lining behind the tiles or the subfloor beneath them. The tiles become waterlogged, absorbing moisture from behind, which causes the darker, damp appearance.

IS YOUR SHOWER GRATE INSTALLED CORRECTLY?

A shower grate must always be installed into a puddle flange, which acts as a barrier to ensure any water that seeps through the tiles and onto the waterproofing is directed into the plumbing system. For the system to work correctly, the shower grate must also have a connected pipe that sleeves into the puddle flange, ensuring water cannot escape anywhere except into the trap and drain.

The grate should be positioned at least 50mm away from each wall, as the puddle flange fitting is usually around 200mm in diameter. If the grate sits too close to a wall or appears misaligned, it’s often a sign that the puddle flange is missing or incorrectly installed, which can lead to leaks and water damage

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CHECKING SHOWER BASE FALL (AS 3740 & NCC COMPLIANT)

To ensure your shower drains correctly and complies with current standards, the shower base must have a minimum fall towards the waste outlet:

• Enclosed showers (with a hob, screen, or door): 1:100 minimum fall (1 mm for every 100 mm of distance).
• Unenclosed showers (wet rooms or open showers): 1:80 minimum fall (1.25 mm for every 100 mm of distance).

How to check: Place a level on the shower base, with one end positioned at the waste and the other against each wall or edge. You should be able to measure the correct fall as per the ratios above.

Visual indicator: A well-installed shower base typically has split tile lines running from each corner of the shower to the waste outlet. These splits help create the necessary slope for water to flow effectively. If the tiles appear flat, or if there are no visible splits, the shower base may not have sufficient fall, increasing the risk of water pooling and leaks.

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HAS YOUR SHOWER BEEN FITTED A WITH COMPLIANT WATER STOP?

A water stop is mandatory under NCC  and AS 3740 to prevent leaks and ensure your shower is correctly waterproofed. It must be installed around the external perimeter of the shower base to contain water and direct it back to the waste outlet.

What Are the Options?

A compliant water stop can be:

• A  hob – A raised, waterproofed, tiled barrier (typically 80–100 mm high). Timber hobs are never compliant.
• An aluminium angle – Must protrude at least 5 mm above the finished tile height and be fitted with an aluminium channel cover so the shower screen can sit on top and overhang inside the shower, ensuring water drains back into the base.
• A step-down (recessed shower base) – Designed during the build, with the floor lowered and the correct fall installed. Step-downs are rarely possible in renovations, as cutting into concrete slabs or joists requires engineering approval and can compromise structural integrity unless the home was designed this way from the start.

Why a Hob is Often the Best Choice

A masonry hob is a reliable, durable solution because it:

1. Contains water effectively, preventing leaks onto the bathroom floor.
2. Allows the waterproofing membrane to be sealed more securely.
3. Improves drainage, ensuring water flows directly to the waste outlet.
4. Provides a stable base for positioning the shower screen, so water drains back inside the shower.
5. Avoids the engineering challenges of step-downs and is more durable than aluminium angles.

How to Check if Your Water Stop is Compliant

• Look for a raised hob or aluminium strip at the shower entry.
• Check the height: aluminium angles must stick up at least 5 mm above the finished tiles. If your shower screen sits flat on tiles you should not be able to push a scraper or blade  between the bottom of the shower scceen and tiles
• Inspect the shower screen: it should sit on top of the water stop, with the frame overhanging inside the shower.
• Look for visible tile splits and fall toward the drain.
• No visible barrier? A flat transition from the shower to the bathroom floor with no water stop is a sign of non-compliance.

Why This Matters

Without a compliant water stop, your shower cannot meet AS 3740 waterproofing standards, increasing the risk of leaks, water damage, mould, and costly structural repairs.

Think your shower may have failed? Book a $159 Shower Assessment & Rectification Quote and we'll visually assess your shower and recommend the right rebuild.

IS THERE A SCREED BED UNDER YOUR SHOWER BASE TILING TO SUPPORT TILES AND CREATE FALL?

To ensure water drains correctly, a screed bed must be installed beneath the tiles to create the necessary slope. By law (AS 3740 and NCC standards), the minimum fall is 1:100 — meaning the floor must slope at least 1 mm for every 100 mm towards the waste outlet.

A quick way to tell if a screed has been installed is by looking at the height of the water stop or hob.

• If the hob is less than 50 mm high, it’s often a sign that there isn’t enough depth to contain a proper screed bed.
• Without a correct screed and fall, water can pool on the surface or seep under tiles, causing leaks and damage.

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IS THE SHOWER SCREEN INSTALLED CORRECTLY?

For a shower to drain properly and avoid leaks, the shower screen must sit flush with the inside edge of the water stop or hob. If the screen is installed too far back (on top of the hob), water can pool at the base of the screen, overflow underneath, and get trapped inside the shower screen frame — leading to mould, water damage, and premature failure.

It’s also critical that silicone caulking is applied only on the outside of the shower screen frame, never on the inside. This allows any water running down the glass and collecting inside the frame to drain back into the shower, instead of becoming trapped.

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ARE THE SPLITS WIDE ENOUGH TO SUPPORT THE GROUT IN PLACE?

On a compliant shower base, the diagonal splits (tile gaps) connecting each corner to the waste outlet should be at least 1.5 mm wide, or the same width as the other grout lines on the base. Anything narrower than 1.5 mm won’t hold enough grout to properly fill the joint and bond to the depth required.

When tile gaps are too tight, the grout becomes weak, falls out over time, and allows water to seep underneath the tiles, leading to leaks and water damage.

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HAVE YOUR SHOWER BASE TILES BEEN LAID PRIOR TO THE WALL TILES?

To meet National Construction Code (NCC) requirements and ensure a watertight shower, the base tiles must always be installed before the wall tiles.

Unfortunately, many tilers install wall tiles first, then lay the base tiles during the same visit to save time — as wet base tiles can’t be walked on to tile the walls. This shortcut creates a major waterproofing risk:

• If wall tiles are laid first, water can run down the walls and seep into the junction between the wall and base tiles.
• When the base is tiled first, followed by the wall tiles, water is directed straight into the waste outlet — not trapped at the base junction.

This order of installation is critical to achieving NCC-compliant waterproofing, preventing hidden leaks and long-term damage.

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