1Start with a proper visual inspection
A shower has several possible routes for water: the waste, supply pipework, tray, silicone or mastic seals, enclosure or door, tiles and grout. I start by looking carefully at all of them.
Quite often the fault is obvious: failed sealant, loose or damaged tiles, a badly fitted enclosure or a door seal that has failed. In my experience, most shower leaks are something ordinary like this rather than a pipe suddenly coming apart underneath the floor.
Do not discount the obvious just because it has been like that for ages. This is one of the biggest things I see in the real world. Somebody will point to a cracked grout line, a tired seal or a loose tile and say, “That’s been like that for years.” My answer is: exactly. It may have been letting a tiny amount of water through for years as well.
A shower leak does not have to pour through the ceiling on day one. A small amount of water can soak into the wall, floor or timber for a long time before the first stain or drip finally appears downstairs. By then the original little defect may have become a much bigger problem.
Have a proper look: do not dismiss a failed seal, cracked grout, loose tile or badly fitted door because it is old or familiar. You see your bathroom every day, so it is surprisingly easy to stop noticing something that is not right. In my experience, the obvious-looking fault is very often the actual fault.
2Test the waste without wetting anything else
If nothing is obvious, I remove the shower head and put the hose directly into the waste. I let it run for around 10–15 minutes so the water goes straight down the plug hole without touching the tray edges, silicone, tiles or shower door.
If water appears below: I investigate the waste, trap and waste pipework next. If it stays dry: I have eliminated one of the main possible routes and move on.
3Stand in the tray and check for movement
A shower tray can look perfectly solid until somebody stands in it. On timber floors there can be movement, and if a tray has not been supported properly even a tiny drop can open the silicone seal.
If the tray moves, simply smearing more silicone over the gap may not solve the underlying problem. A small amount of movement can sometimes be tolerated by a good seal, but if the tray is moving significantly it needs supporting properly before it is resealed.
4Test the shower door and enclosure
I reconnect the shower head and simulate somebody actually using the shower, deliberately spraying the enclosure and watching where the water travels.
A common fault is an enclosure that has been installed or sealed incorrectly. Many modern shower enclosures are designed so water inside the profiles can drain back into the tray. If the enclosure has been sealed in the wrong places, water can become trapped in a profile, run down behind it and disappear between the tray and wall.
Sometimes the proper repair means removing the enclosure or wall profile and reinstalling and sealing it correctly — not adding another bead of silicone over the top.
5Pressure-test concealed shower outlets before opening a wall
If I suspect concealed shower pipework, I do not start smashing tiles off. I cap or plug the shower outlet, turn the shower on and leave the outlet side under pressure without spraying water around the enclosure.
If water appears below while the outlet is capped: that is strong evidence of a concealed outlet or supply-side fault. If it stays dry: I keep eliminating other causes.
6Check the tiles and grout — especially the bottom courses
In a small shower, a surprising amount of water hits the walls. It runs down the face of the tiles and across the grout joints. A cracked or missing grout line can give water a direct route behind the tiles.
I pay particular attention to the bottom rows. I will tap the tiles with my knuckle and listen. Higher tiles may sound solid while lower ones sound hollow, which can be a clue that water has been getting behind them. Tray movement can also stress the lowest grout joint and create exactly this sort of route.
7Use the least destructive access
Taking tiles off is a last resort. If an older bathroom has no spare matching tiles, opening a wall can create a much bigger reinstatement problem than the original leak.
Sometimes the sensible route is from the ceiling below. Modern bathroom floors can contain tiles, membrane, ply, floorboards and even underfloor heating. A plasterboard ceiling can be far easier to repair. I have opened ceilings or fitted temporary access panels, repaired the fault, then left access available long enough to prove the shower stays dry before the ceiling is finally made good.
8Do not forget the unusual faults
I once worked through all the normal checks and still could not reproduce the leak. Eventually I gained access underneath the tray and found an almost pinhole-sized crack in the tray itself. From above it was virtually invisible until I knew exactly where to look.
That is why leak diagnosis is a process. Start with what is most likely, prove or eliminate it, then keep going until the water gives the answer.
A real-world approach
Find the leak before you start wrecking the bathroom
Most of the time, shower leaks are not rocket science. Water will find a failed seal, a cracked grout line, a badly fitted enclosure, a faulty waste or another route and travel downwards. The skill is knowing what to check, in what order, and when not to start pulling somebody's bathroom apart.
I have worked in every kind of home and the basic problems are remarkably similar. Start with the easy, obvious possibilities and only move towards destructive investigation when the evidence takes you there.
S R Francis Ltd provides plumbing and shower leak diagnosis across Bromley, Bickley, Beckenham, Hayes, Keston, Petts Wood, Orpington, Chislehurst and Biggin Hill.
