The call came in as a rising damp problem in a Hampstead flat. Damp had spread around the property, and the bedroom reading later came back over 30%.
Once we took the bath panel off, the cause looked much more direct. The waste trap under the bath had come completely off, so bath water dropped onto the floor every time the customer used it.
The bath panel had hidden the fault. That delay allowed water to travel under floors and into adjoining rooms, which can lead to swollen skirting boards, damaged flooring, mould, and unnecessary damp-proofing quotes.
Why a Bath Waste Leak Looks Like Rising Damp
True rising damp usually starts from the base of a wall. It comes from moisture moving up through masonry, often where a damp proof course has failed or can no longer do its job.
A leaking bath waste behaves differently, but it can look similar inside a flat. Water runs under the bath, spreads across the floor void, and appears at walls some distance from the bathroom.
London flats make this worse. Many Hampstead and central London properties have boxed-in pipework, fitted bath panels, tight service voids, and old timber floors. Water can travel a long way before anyone sees it.
That matters because the repair changes completely. Damp proofing will not fix a loose bath trap. You need to stop the water at source, check every nearby connection, and dry the structure before you redecorate.
Treat the Damp Report as a Leak Until You Prove Otherwise
Start with the simple question: where can water escape? Check the bathroom, kitchen, heating pipework, radiators, shower seals, waste pipes, and appliance connections.
On this Hampstead job, the pattern of damp made us look hard at the bathroom. The customer had not checked under the bath because the side panel covered the space completely.
Do not assume damp near a skirting board means rising damp. A failed bath waste, shower leak, or hidden pipe joint can produce the same signs. Look for staining, musty smells, loose flooring, and damp readings away from external walls.
Remove the Bath Panel and Expose the Waste
Take the bath panel off carefully before you run more water. Many plastic panels flex and crack, while tiled panels may need more care to avoid damage.
Once we removed the panel, we could see the first major fault straight away. The bath waste trap had come away from the bath outlet, leaving an open route for water to fall below the tub.
This is a common problem after movement, poor fitting, cross-threaded fittings, or a trap that never had enough support. Waste pipework needs fall, alignment, and secure compression connections.
Run the Bath and Trace the Waste Route
Test the waste in a controlled way. Use a small amount of water first, keep towels ready, and watch every joint from the bath outlet to the soil or waste run.
On this job, the first leak did not tell the whole story. We also found a second serious leak further down the waste pipe at another connector.
This is why we do not stop at the first obvious fault. Water can loosen fittings downstream, and one hidden leak can mask another. A proper plumbing inspection follows the whole route.
Replace the Trap, Overflow and Failed Connector
We replaced the faulty bath trap and the overflow connections. We also repaired the second leaking connector further down the waste run.
Bath waste parts look simple, but the fit matters. The rubber seals need clean mating faces, the trap needs correct alignment, and the pipework must not pull against the fitting.
After fitting the new parts, run the bath again and check under load. Fill the bath enough to test the overflow as well as the normal waste. Then release the water and watch the joints while the pipework carries a full flow.
Our plumbing rate is £90 per hour plus VAT, which is £108 including VAT at 20%. A leak investigation like this often starts with one to two hours to expose, test, and diagnose the fault, then parts and repair time follow.
Basic bath waste traps and overflow parts often cost around £20 to £70, depending on type and access. Larger remedial work, flooring repairs, or decorating after water damage needs a separate quote.
Measure Damp Levels and Start Controlled Drying
Stopping the leak does not instantly dry the flat. Moisture can sit in floors, plasterboard, insulation, timber, and behind skirting boards.
We checked damp levels in the bedroom and found a reading over 30%. That told us the water had travelled beyond the bathroom area.
We advised the customer to use a dehumidifier to pull moisture out of the rooms. Keep internal doors open where practical, allow air to move, and empty the dehumidifier regularly unless it drains continuously.
Do not redecorate too early. Paint, filler, and wallpaper can trap moisture and fail again. Take follow-up readings before you spend money on finishes.
Plan the Drying Time Before You Repair Finishes
Drying time depends on how long the leak ran, what materials absorbed the water, and how well the flat can ventilate. A small surface leak may dry in days. A leak under a bath that reached another room can take much longer.
Cold weather slows drying. So do sealed floors, fitted cupboards, vinyl, laminate, and closed-up rooms. Winter leaks in London flats often need steady heat and dehumidification rather than open windows all day.
Watch for mould during the drying period. Clean light surface mould with the correct product, but treat recurring mould as a sign that moisture remains. If electrics, sockets, or lights may have got wet, isolate the circuit and ask a qualified electrician to inspect it.
Landlords should also keep clear records. Note the leak source, repair date, damp readings, drying advice, and any follow-up inspection. Damp and mould can raise safety and habitability concerns if nobody deals with the source properly.
Most importantly, do not pay for damp proofing until someone has checked the plumbing. In this Hampstead flat, repairing the detached trap and the second leaking connector stopped the cause. As the structure dried, the damp problem disappeared.
Frequently Asked Questions
Q1: Can a bath leak really look like rising damp?
Yes. Water can travel under floors and appear at walls away from the bathroom. That can make a plumbing leak look like damp rising from the ground.
Q2: Should I remove the bath panel myself?
You can remove a simple clipped plastic panel if you feel confident. Stop if the panel has tiles, sealant, or awkward fixings, as you can cause damage quickly.
Q3: How much does leak investigation cost?
Our plumbing rate is £90 per hour plus VAT, which is £108 including VAT at 20%. Many hidden bathroom leak checks take one to two hours before parts or extra repairs.
Q4: How long should I run a dehumidifier after a leak?
Run it until damp readings fall back and the affected areas feel dry. A serious leak under a bath can need days or weeks of controlled drying.
Q5: When should I call a professional plumber?
Call a plumber if damp keeps spreading, the leak sits behind panels, or you see water near electrics. A professional inspection helps you avoid guessing and stops the damage at source.
The main lesson from this Hampstead flat is simple: check hidden plumbing before you treat damp as a building defect. Kensington Maintenance Services Ltd found the detached bath trap, repaired the second leak, replaced the faulty waste and overflow connections, and gave drying advice based on the damp readings. If your flat has unexplained damp, especially near a bathroom, contact our team at https://www.kensingtonmaintenance.co.uk/about-us/contact-us/ and we will trace the cause before you spend money on the wrong repair.