The question the whole job turns on
A bathroom leak is one of three things, and they are fixed in completely different ways:
- A pressurised plumbing leak. A hot or cold supply pipe, a concealed valve body, a flexible tail. It leaks whether or not anyone uses the room, and it usually gets worse.
- A waste leak. A trap, a waste pipe joint, a bath or tray waste, a soil connection. It only leaks when water is running down it, so it appears in bursts and stops.
- A waterproofing failure. Grout, silicone, a tray seal, a perished tanking membrane in a wet room. Water goes past the tiles and runs somewhere it should not. It only happens when the shower or the bath is used, and it often gets blamed on the plumbing for months.
Telling them apart is the entire skill in this job. Get it wrong and you re-tile a room whose real problem was a compression nut on a waste, or you renew a silicone bead three times while a valve body drips behind the tiles.
How the visit runs
- Look underneath first. Where a ceiling below is already stained, that stain map tells you a great deal before anything in the bathroom is touched — a mark directly under the tray is a different problem from one under the doorway or the far wall.
- Static test. The bathroom is left completely unused with the supply on. Damp that grows with nothing running means a pressurised leak, and the room is tested with a pressure gauge and the supply isolated section by section.
- Waste-only test. Water is run down the bath waste, the basin waste and the shower waste separately, each with the others dry, and the joints are watched. A leak that appears with one waste and not the others has just identified itself.
- Flood test the tray or bath. The waste is blocked and the tray or bath stands full. If water appears with the tray full and nothing running, the leak is the tray, its seal or its bedding — not the plumbing.
- Dye test where the route is ambiguous. A traceable dye put into one appliance shows which one is feeding the stain below when several are suspects.
- Spray test the enclosure. The shower is run onto the screen junctions, the tile field, the tray upstand and the door seal in turn, to see which one lets water past.
- Open only what is needed. Access is taken through a bath panel, a boxing, a cupboard back or the ceiling below in preference to the tiled face of a wall. Where we do have to go through tiles, we ask about spares first.
What we most often find in London bathrooms
- A failed seal where the tray or bath meets the tiles. Silicone that has been painted over, or grout used where a flexible joint was needed. It cannot cope with a bath flexing as it fills.
- A shower tray sitting on an inadequate bed. The tray rocks a fraction under a person's weight, which breaks the perimeter seal repeatedly no matter how many times it is renewed.
- A concealed thermostatic valve body weeping behind the tiles. Slow, constant, invisible, and it will have been running for a long time before the ceiling below shows it.
- A waste trap compression nut backed off, or a trap that has been knocked by something stored under a basin.
- A bath overflow connection that only leaks when the bath is filled above the overflow — which happens about once a month, hence a stain that appears without any pattern.
- Wet room tanking that stops short. The membrane finishes below the level water reaches, usually at a doorway or behind a fitted screen.
- A soil pipe collar behind the WC, which smells before it stains.
- A leaking flexible tail on a basin or WC, braided hose perished at the crimp.
If the symptom you have is water appearing on a ceiling below, shower leaking through the ceiling and bath leaking through the ceiling narrow it down before you call anyone.
The repair
Seals and grout are cut out, the substrate dried, and the joint remade in the right material for a moving junction. Wastes and traps are replaced rather than re-tightened where the thread or the seat is damaged. Concealed valves are reached through the smallest viable opening, repaired or replaced, and left with an access route for next time rather than tiled over blind. Supply pipework is repaired, re-run or replaced as the run requires — see pipework repair and replacement. Trays that rock are lifted and re-bedded, because no seal survives a moving tray.
The making good, above and below
A bathroom leak damages two rooms. Ours is the only half of this trade that routinely puts both back. Tiling refitted or replaced, grout and silicone renewed to match, boxing and panels remade, and downstairs the ceiling cut back to dry board, re-boarded, taped, skimmed, stain-blocked and painted. That is our reinstatement team, in-house. The ceiling side of the job is covered in more detail on ceiling leak repair.
As always, the ceiling goes back once it reads dry, not the same afternoon. A ceiling closed over a wet void blooms within weeks.
What you can fix yourself
Genuinely, before calling anyone:
- A perished silicone bead round a bath or tray. Cut the old one out completely, dry the joint thoroughly, and reapply a sanitary-grade silicone. This solves a real proportion of "shower leaks". Do not apply new silicone over old.
- A loose trap nut under a basin. Hand-tighten it, dry the area, and run the tap while watching.
- Cracked grout in the tile field. Rake it out and regrout.
- A dripping tap. That is a washer or a cartridge, not a leak investigation. See a dripping tap.
Call us when the ceiling below is wet or sagging, when the damp is there with nothing running, when the leak has come back after the silicone has been redone twice, or when you cannot tell which of the three causes above you have. A sagging ceiling should not wait.
What it costs
Charged at our hourly rate, fixed before we attend, plus materials. The rate cannot rise once agreed; the total depends on how many tests are needed to isolate the cause and how much reinstatement the two rooms need. If we cannot find the source, you do not pay for the time we spent looking. Terms on the pricing page, and if you are claiming, the report is written for a trace and access claim.
