Around 55 to 65 per cent of Australian showers leak. Membranes typically give out somewhere between their tenth and fifteenth year, which puts almost every untouched shower in the older Berwick estates inside the failure window right now. The trouble is that a dead membrane and a grout problem look identical for the first year or two.

Both show dark grout and a bit of mould, and both get treated with a tube of sealant. Only one of them keeps getting worse behind the tiles, and the repairs are not remotely comparable: a grout problem is cosmetic and takes a day, while a failed membrane means water has been running into wall and floor framing for months or years.

The signs inside the bathroom

These are the early signs, and they tend to arrive in roughly this order.

Grout going dark in one specific area, usually at the base of a wall or in an internal corner, while the rest of the grout keeps its colour. Grout that is evenly grubby is dirt. Grout that is dark in one patch is holding water.
Silicone in the corners lifting, splitting or going black underneath. Black mould living under the silicone rather than on top of it means water is getting in behind.
A tile that sounds hollow when you tap it. A drummy tile means the adhesive bond has failed, which usually means the substrate behind it is wet or has moved.
Efflorescence, a white chalky deposit along the grout lines. That is salt left behind by water that has passed through the mortar bed and evaporated. It is not soap scum and cleaning does not keep it away.
A floor or hob tile that lifts or cracks along the same line every time it is repaired. The material under it has gone soft.
The room staying damp for hours after a shower. In the 1980s belt that is frequently the exhaust fan emptying into the roof cavity, which is a problem in itself and also good at hiding a real leak.

The signs on the other side of the wall

This is where a membrane failure gives itself away, because grout does not put water into the next room.

Where to look	What a failed membrane produces
The skirting board on the far side of the shower wall	Paint bubbling or flaking along the bottom edge, or the skirting swelling and pulling away
The carpet or floorboards in the adjoining room or hall	A damp patch that never fully dries, a dark line along the wall, carpet backing perished at the edge
The plaster on the far side of the shower wall	A tide mark, a soft patch that gives under thumb pressure, paint lifting in a horizontal band
The ceiling of the room below, in a two storey home	A brown stain, a sagging sheet, or a rusted screw head showing through the paint
The subfloor, in a house on stumps	Damp or rotted joists and bearers under the shower, visible from the crawl space
The external brickwork below the bathroom	Persistent damp staining, moss growing in one vertical strip, salt deposits on the bricks
Inside a vanity cupboard sharing the wall	Swollen particle board at the back or base, and a musty smell

A smell is worth taking seriously on its own. A bathroom that smells musty after being closed up for a day, with no visible mould anywhere in the room, generally has wet material inside the wall or under the floor.

Grout problem or membrane failure?

Signal	Grout problem	Membrane failure
Age of the shower	Any age	Usually over 10 years
Where the damage shows	Inside the shower only	Also outside it: skirtings, adjoining rooms, the ceiling below
Does it dry out between uses	Yes	No, the area stays damp
Response to sealing the grout	Improves for months	Unchanged or worse, because the water is now trapped
Drummy tiles	Rare	Common
Efflorescence	Rare	Common
Floor waste	Draining normally	Sometimes slow, sometimes water pooling away from the waste

Which checks can you run yourself?

The block and fill test on the shower base. Block the floor waste with a test plug, fill the base to just below the hob, mark the level and leave it 24 hours with no water used in the room. A level that drops with no explanation means water is leaving the base through something other than the waste. Only do this where the hob is deep enough to hold water safely, and never where damage is already showing in the room below.

The dry room test. Stop using the shower for four days and wash elsewhere. If the damp patch in the hall, the bubbling skirting or the musty smell eases over those four days, the shower is the source. If nothing changes, the water is arriving from somewhere else: a leaking waste, a burst pipe inside the wall, or rising damp.

Neither test tells you whether the membrane or the waste connection is at fault. Finding that out means opening the shower up.

Why does a re grout not fix a leaking shower?

Grout is not a waterproof layer and it was never designed to be. Every tiled shower lets some water through the grout and the tile bed by design. The membrane underneath is the layer that stops it, and it carries that water back to the floor waste through weep holes. When somebody says their shower is leaking, they nearly always mean that hidden layer has given up.

Re grouting replaces the visible mortar between the tiles and does nothing at all to the membrane two layers below. In a shower where the membrane has gone, a re grout has two effects: the room looks better for a while, and water that used to evaporate through the old porous grout now stays in the wall. That is why so many showers get visibly worse in the six months after one.

There is one honest use for a re grout. A shower under about eight years old, with the damage confined inside the room, no drummy tiles, and nothing ever appearing on the far side of the wall. Outside those conditions it is money spent on delay. The same goes for the surface sealers sold as a fix that avoids removing tiles: they buy time on a sound membrane and seal the water in on a failed one.

What does a proper repair involve?

Remove the screen, the tiles, the mortar bed and the old membrane back to the substrate.
Cut out and replace any wet or rotted wall sheet, framing or floor material. In a Berwick timber floored house this is routinely the largest unknown in the job.
Correct the falls in the base so water actually reaches the waste.
Re sheet with wet area sheet, then prime, install bond breakers at every junction and apply the membrane in two coats.
Let the membrane cure properly before the tiler starts.
Tile, grout, silicone, and refit the screen.

Step 4 is the one worth checking in writing. The membrane standard and the height it has to reach up a shower wall are both set by regulation, and the figures are on what the law requires. A quote that names neither has not been written by someone who reads them.

That sequence is five to eight working days for a shower only rebuild. The calendar for a whole room is on how long a bathroom renovation takes, and the price bands are on what a bathroom renovation costs in Berwick.

How this looks across Berwick

The early 1990s estates are the clearest case. Those houses are now 30 to 35 years old, which is two to three times the normal life of a membrane, so a shower there that has never been rebuilt has not been at risk of failing, it has already failed. The only open question is how much framing is wet. Layout and plumbing in that stock are sound, so the fix is a same footprint rebuild.

In the 1970s and 1980s brick veneer belt the shower usually sits over a steel bath, which hides the wall junction where the failure starts. A leak there runs down the outside of the bath and into the floor without ever showing itself in the room. Anything in that belt built before 1990 also needs its sheeting tested before a wall comes off.

In the heritage core around High Street the timber floors and uneven levels give a long running leak somewhere to go, and the rot found under an old shower there is routinely worse than the surface suggested it would be.

If you have any of the outside the wall signs above, get it looked at. Shower repairs and waterproofing is a scoped job with a written fixed price, and you can send photos through the quote form for a reply within one business day.

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How to tell if your shower is leaking