Wet Room Leaking? How to Tell If It Needs Stripping and Re-Tanking

If your wet room is leaking, the problem is almost never the grout. Tiles and grout are decorative and water resistant, not waterproof: the layer that actually keeps water in the room is the tanking membrane underneath, and if water is showing on the ceiling below or damp is tracking into the next room, that membrane has failed somewhere. The honest question is not how to reseal it, but whether the floor needs stripping back and re-tanking properly.

After 44 years tiling, a good share of my wet room work is now putting right installations that failed within a few years. Here is how I diagnose them, and how to judge what yours needs.

Key takeaways

• Grout and tiles are not the waterproof layer. If water is getting out, the tanking beneath has a gap or was never done.
• Recurring damp after a regrout or reseal is the classic sign the membrane itself has failed.
• Surface repairs only work for silicone joints, drain fittings, or plumbing faults, not membrane failure.
• A proper re-tank means stripping to the substrate, rebuilding falls, tanking the whole wet zone, and flood testing before a single tile goes down.
• Get the diagnosis and the repair specification in writing before agreeing to anything.

A Beckenham wet room built on a fully tanked, flood-tested base. The marble is the visible part; the waterproofing underneath is what makes it a wet room. Wet room installation service

Why is my wet room leaking?

A wet room holds water for one reason: a continuous waterproof membrane runs across the floor, up the wet walls, and bonds into the drain. Everything else sits on top of it. Water passes through grout joints in normal use, that is expected, and the membrane catches it and sheds it to the drain.

So when water escapes, one of two things has happened. Either a joint that was meant to be flexible has failed (silicone at the wall-to-floor junction, the seal at the drain clamping ring, a pipe connection boxed in behind the tiling), or the membrane itself has a breach. The first group is repairable. The second is not, at least not from above.

The distinction matters because most homeowners are told to regrout or reseal first. If the leak stops permanently, fine, it was a joint. If damp comes back within weeks, you have your answer: the water was never escaping through the grout, and every reseal from here is money spent delaying the real job. I cover why grout gets wrongly blamed in leaking shower: grout, sealant or tanking.

What are the signs the tanking has failed?

These are the things I look for on a diagnosis visit:

• Damp or staining on the ceiling below that returns after a regrout. The strongest single indicator. If it recurs, the membrane is breached.
• Damp tracking at skirting level in the adjoining room. Water escaping at the wall-to-floor junction travels sideways before it shows.
• Hollow or drummy tiles in the wet zone. Repeated soaking debonds adhesive. Tap the floor: a hollow note over a widening area suggests water underneath. More on this in hollow and drummy tiles.
• A musty smell that cleaning does not shift. Saturated substrate under the tiles, often timber, quietly rotting.
• Movement or spongy feel underfoot. On a timber subfloor this is serious: the boarding is losing strength.
• Grout that keeps cracking along the same lines. Usually the substrate moving because it is wet, not a grouting fault.

One of these alone is not a verdict. Two or three together, in a room where the leak has already been “fixed” once, usually is. If water is actively coming through a ceiling, treat it with urgency and read shower leaking through the ceiling for the immediate steps.

Can a leaking wet room be repaired without stripping it?

Sometimes, and a decent tiler will always check the cheap causes first. The drain clamping ring can be accessed and re-seated. Perished silicone can be cut out and redone properly. A plumbing fault behind an access panel is a plumber’s job, not a tiling one.

What cannot be done is re-waterproofing a floor through its tiles. Painted-on grout sealers and “leak repair” liquids applied over the surface do not reach the membrane and do not bond as one. I have stripped out floors where three rounds of miracle products had been applied over as many years while the joists underneath went black. The kindest thing I can tell you on a survey is the truth: patch what is genuinely patchable, strip what is not.

What does stripping and re-tanking actually involve?

Done properly, it is a rebuild of the floor’s whole waterproof system:

1. Strip back to the substrate. Tiles, adhesive bed and the failed membrane all come out. On timber floors, any rotten boarding or noggins are replaced.
2. Inspect and rebuild the base. The substrate must be rigid and dry. On timber this usually means a cement-based tile backer board over the joists; on concrete, repair and priming.
3. Reform the falls. A wet room floor must drain to the outlet from every direction. If the original falls were wrong (a very common original sin), a preformed shower former or a screeded fall puts that right.
4. Tank the whole wet zone. A full liquid membrane system such as Mapei Mapelastic or BAL Tank-it, or a sheet system like Schluter Kerdi, across the entire floor and up the wet walls, with reinforcing tape bedded into every wall-to-floor junction, internal corner and pipe penetration. What tanking is and why it is non-negotiable is covered in what is tanking.
5. Bond the membrane to the drain. The drain flange and membrane must form one continuous system. This junction is where most failed wet rooms I open up went wrong.
6. Flood test before tiling. Plug the drain, fill the floor, leave it, check below. Cheap insurance against ever doing this twice.
7. Retile on a C2 adhesive with movement joints where the substrate changes and proper silicone at every internal corner.

Nothing on that list is optional, and every stage needs its cure time. That is why the honest quote for this work is never the cheapest one. The same principle applies to quotes for new wet rooms, which I cover in what affects wet room cost.

Why do wet rooms fail in the first place?

Because a wet room is a construction job sold as a tiling job. The failures I open up are rarely mysterious: tanking applied only inside the shower footprint with the rest of the floor left bare, no reinforcing tape at the junctions, a membrane lapped loosely over the drain instead of bonded to it, falls so shallow that water pools against a wall, or a timber floor tiled without proper boarding so the whole system flexed until it cracked. Every one of those is a corner cut on day one, invisible under the finished tiles, and inevitable within a few years.

Fixing failed wet rooms in Beckenham and South East London

I see this most in the Edwardian and Victorian housing around Beckenham, where wet rooms have been built over original timber floors. These houses take wet rooms very well, but only when the substrate is rebuilt rigid and the tanking is continuous; the original floors move too much for shortcuts to survive. I strip, re-tank and rebuild wet rooms across Beckenham, Bromley and the surrounding areas, and you can read how I approach them locally on my wet room installation in Beckenham page.

If your wet room is leaking, do not commission another regrout on hope. Have it diagnosed, get the findings and the repair specification in writing, and fix it once. Get in touch and I will take a look and tell you straight whether yours is a repair or a re-tank.

See: what is tanking | shower leaking through the ceiling | leaking shower: grout, sealant or tanking