Half past seven on a Tuesday, third floor, doors open ninety seconds. The washroom looks immaculate – chrome dry, mirrors clear, floor still faintly damp along the skirting, bin liner squared off at the corners. And it smells of ammonia and something sweet laid over the top of it, which is the worst version, because the sweet part is the air freshener trying and failing. By ten o’clock it will have gone. By the following morning it will be back. Somebody will email the cleaning company, the cleaning company will send a supervisor, the supervisor will find nothing wrong with the clean, and the cycle repeats until either the tenant changes contractor or someone finally works out that the smell has almost nothing to do with what happened at nine the previous evening.
Where is the smell actually coming from?
The floor. It is nearly always the floor.
Urine is mostly water and urea when it leaves the body, and within a few hours bacteria break the urea down into ammonia and a set of uric acid salts. Those salts are the problem. They are crystalline, they bind to porous surfaces, and they do not dissolve in water – which means a mop and a general-purpose neutral detergent will slide straight over them and leave them exactly where they are. Add warm water and you rehydrate the salts just enough to get them volatilising again a few hours later. Every night clean, on some floors, is a small reactivation event.
They accumulate in grout lines, in the porous edge of a cut vinyl tile, in the joint where the tiling meets the skirting, and behind the pedestal of a WC pan where nobody has ever put a cloth. On a busy Wednesday a 200-person floor might see 400 uses of a two-bowl urinal, and a proportion of every one of those is going onto the floor rather than into the bowl. Ten years of that in a building with unsealed grout produces a floor that smells regardless of how well it has been mopped.
The half-metre splash zone
Draw an imaginary semicircle half a metre out from the front of every urinal and every WC pan. That is the zone. Get down on your knees in it with a torch and look at the grout colour against the grout two metres away, and you will usually see the difference before you smell it – a yellow-brown tidemark following the line of the appliances.
That zone needs an acidic descaler or a properly dwelling enzymatic product, applied, left to work for its stated contact time, agitated with a deck brush and extracted rather than pushed around. Ten minutes of dwell time is not optional. Most night teams are given four minutes for the entire washroom.
Why does it come back overnight if the washroom was clean at ten?
Two things happen between the cleaner leaving and the first person arriving, and both of them are building services rather than cleaning.
The first is ventilation. Sanitary accommodation in an office should have extract running at around 6 litres per second per WC, and in most London buildings that extract is wired into the BMS alongside the lighting and the air handling. Out of hours, everything drops back. So from about eight in the evening until the plant ramps up around seven, you have a sealed warm box with no air changes and a floor slowly off-gassing ammonia into it. The smell is not being produced overnight so much as concentrated overnight. Open the door at 7.30 and you get twelve hours of it in one go. By ten, when the extract has been running for three hours, it has cleared – which is why the facilities manager who investigates at eleven o’clock never finds anything.
The second is flushing, and this is the one almost nobody checks.
Your urinal controller stops flushing at seven
The Water Supply (Water Fittings) Regulations 1999 cap automatic urinal flushing at 7.5 litres per hour per bowl where a cistern serves two or more urinals, and require a device that stops the cistern filling when the building is empty. Sensible regulation – urinals used to flush all night for nobody. The controllers that deliver it work off a PIR sensor, a hydraulic pressure drop from the taps, or a time switch.
Here is what goes wrong. A good controller runs a hygienic flush after a set period of no detected use, typically every twelve hours, precisely so the bowl and trap do not sit loaded with concentrated urine all night. A cheap one does not. A time-switch installation set to office hours in 2016 and never touched since does not. So the last flush of the day happens at about half past six, and then a two-bowl urinal with the day’s residue in the trap sits at 22 degrees until Wednesday morning. Thirteen hours of anaerobic bacterial activity in a warm sealed room, and the cleaner who came through at nine had no way of affecting any of it.
We found exactly this in a serviced office off Great Portland Street. Two floors, identical fit-out, identical cleaning spec, one floor fine and one floor foul every morning. The difference was a failed solenoid on the fourth-floor controller that had been flushing on a fixed daytime schedule for two years. A plumber replaced it for about £180 and the problem vanished. We had been on site for eleven weeks by then, being blamed.
While we are here: waterless urinals should never have been fitted in general-access office washrooms, and I will argue that with anyone. The sealant cartridge principle is sound in a controlled environment with a disciplined maintenance regime. In a building where a relief cleaner will eventually pour bleach down one because it smells, the oil seal breaks, the chlorine hits the urine, and you get a far worse smell plus a trap full of uric scale in a pipe run that was never designed to be flushed. The water saving is real. It is not worth what follows.
Is the cleaning method feeding the problem?
Sometimes, yes, and this is the part we can be held responsible for.
What the mop is moving around
A flat mop or a string mop taken from the WC floor to the corridor and back into the same bucket does one useful thing and one destructive thing. It lifts visible soil, and it redistributes uric salts in a thin film across a wider area, including out through the door into the lobby carpet. If your washroom smells at the threshold rather than at the appliances, you are looking at a mop routine.
Colour-coded systems exist to prevent this and are on every contractor’s method statement, including ours. What matters is whether the sanitary mop head goes into the laundry every night or gets rinsed in the same slop sink and hung damp until Thursday. Ask to see the mop store. Get down on your knees and look under the shelf.
The other common error is chemical. Neutral detergent every night, forever, with no acidic descale in the rotation, on the reasoning that acid is aggressive and the tiling is expensive. Twelve months of that and the grout is loaded. The correct answer is a scheduled acidic treatment of the splash zone on a fixed cycle – weekly in a heavy-use core, monthly in a quiet one – with neutral cleaning in between.
When is it the building rather than the cleaner?
When the smell survives a properly executed descale. That is the test, and it is a cheap test to run.
The pan that has been leaking underneath itself
Failed sealant at the base of a WC pan is the classic. Urine wicks under the pan into the screed, and the screed holds it indefinitely. No surface cleaning reaches it. The fix is to lift the pan, kill the contamination, reseal and reset – a plumbing job costing a few hundred pounds that will outperform any cleaning intervention you could buy.
Then there are voids. Duct panels behind the pans, IPS panelling with a gap at the floor junction, and the space under a raised access floor where a leaking spigot has been dripping for a year. We had a case in an office on Old York Road in Wandsworth where the smell was coming through a floor box eight metres from the washroom, tracking along the void from a cracked WC connector. Nothing on the surface would ever have touched it.
Older buildings around Stratford and the E15 fringe throw up another one: cast iron soil stacks with degraded joints in the riser cupboard, venting into the washroom every time the stack takes a slug of water from the floors above. That smell arrives in waves rather than sitting constant. If it comes and goes on a rhythm, stop looking at the floor.
What should you stop paying for?
Two things, and we sell both of them.
The fragrance unit works against you
Scent diffusers first. The battery-powered aerosol units and the plug-in fragrance systems on a monthly rental are the single most effective way to delay diagnosis of a washroom odour problem, because they lower the complaint volume without changing anything. We sell them. We would rather you cancelled them until the underlying cause is fixed, because the fragrance and the ammonia together produce that sweet-sour note everyone recognises and nobody can name.
Stop paying for repeat deep cleans, too. One properly specified acidic descale of the splash zone will tell you whether cleaning is the answer. If the smell is back within a fortnight, buying a second one is money set on fire. We have turned down that second job more than once and told the client to get a plumber onto the flush controller instead.
Get down on your knees at half past seven, before the extract has had a chance to lie to you.