The smell reaches you before the carpet does. You open the door to a ground-floor flat and there it is – that low, earthy note of a damp cellar hanging in the hall, the one that says something has been quietly wet for a long time. The tenant blames the carpet. The landlord blames the carpet. And the carpet takes the blame for a fault that was never its own.
Nine flats out of ten, that smell is the floor talking. The carpet is the messenger – holding onto moisture and feeding whatever’s growing in it – while the water arrives from somewhere underneath or alongside. Spray over the top and you’ve perfumed a problem that’s still there in the morning.
So here is how you find it and finish it, in the kind of ground-floor London flat where this turns up week in, week out.
Where does that musty carpet smell come from?
The smell has a source, and the source is alive.
That damp-cellar note is microbial. Mould and mildew, along with the bacteria that ride in on the same damp, grow in the pile and down in the underlay, and they give off gas as they feed. The gas is the smell. They need two things to do it: moisture, and something to eat. The something to eat is the ordinary soil in any lived-on carpet – crumbs and the fine, greasy dust that works its way down to the base of the pile over the years. Add steady moisture to that and you’ve built them a home with the heating on.
There’s often a second smell layered under the first in older flats. Older carpet has a latex secondary backing, and when latex gets damp and ages it breaks down and gives off a sour, rubbery note of its own. People read that as “dirty carpet.” It’s the glue rotting.
The underlay is where it lives
You can shampoo the face fibre until it’s spotless and the smell will be back by the weekend, because the reservoir isn’t the part you can see. Underlay soaks up and holds far more moisture than the carpet sitting on it, and old felt underlay is the worst offender of the lot – once it’s been damp and gone musty, it’s a sponge full of mould that no cleaning wand on the market reaches. Lift the carpet in a flat like this and the underneath tells you the whole story in one breath.
Why do ground-floor London flats get this more than the flats above?
Because the ground floor sits on the damp, and half of London’s ground floors can’t breathe properly.
Take the Victorian and Edwardian conversions that make up so much of the city’s flat stock. The ground-floor flat usually sits on a suspended timber floor – joists and boards with an open void beneath them, and airbricks set into the outside wall to keep that void ventilated. Keep air moving through the void and the timber stays dry. Block the airflow and the void turns humid, the joists take on moisture, and that damp works its way up through the boards into the underlay and the carpet above.
The airbricks are the whole game, and in London they get blocked constantly. Someone lays a patio and the new slabs sit level with the bricks or bury them outright. A flower bed gets banked up against the wall. A previous owner repaints the front elevation and fills the little terracotta grilles with masonry paint without a second thought. The void stops breathing, and everything above it goes slowly, steadily damp.
Then there’s the other kind of ground floor – the solid concrete slab in a post-war block. These depend on a damp-proof membrane in or under the slab. Where that membrane was never fitted, or has failed with age, ground moisture wicks straight up through the concrete and into whatever’s laid on top. You’ll find it worst around the edges of the room and under the furniture that’s sat flat and unmoved for years.
Garden flats and lower-ground flats have it hardest of all. The floor there can be sitting below the level of the soil outside the wall, so damp pushes in sideways through the brickwork as well as up from below, and a raised path or a neighbour’s higher garden keeps a permanent head of moisture against the structure. I’ve been in lower-ground flats off leafy streets in Dulwich where the carpet felt dry to the hand and the meter still buried itself in the red, because the wall behind the skirting was wet through and feeding the room from the side.
The patio that buried the airbricks
I took a call from a ground-floor conversion off Bellenden Road in Peckham last autumn, the tenant complaining that a carpet fitted only months earlier had “gone off.” The carpet was fine. Out the back, the landlord had had a smart new patio laid the summer before, and the builder had run it straight up to the wall and over two of the three airbricks. The void underneath had been stewing ever since. We could lift and replace that carpet as many times as anyone fancied paying for; until someone reopened an air gap around those bricks, it was going to keep happening. Again, the carpet was taking the blame for the floor.
Can you get rid of it with sprays, powders and a good shampoo?
No, and I’ll be blunt about the products sold for the job.
Most “odour eliminating” carpet sprays are perfume in a can. They lay a pleasant smell over the musty one for a day or two, the perfume fades faster than the damp does, and you’re back where you started with a lighter wallet. Any cleaner who quotes you for a “deodorising treatment” on a ground-floor flat without lifting a corner to look underneath is selling you a smell rather than a fix, and you should show them the door.
Bicarbonate of soda gets talked about like magic. It has its place – sprinkled on and vacuumed off the next morning, it’ll lift a stale, shut-up whiff from a carpet that’s dry underneath. Against live damp rising from a subfloor it does nothing worth the effort. You’re deodorising the top millimetre of a problem that’s four inches down.
Where bicarbonate of soda stops working
The test is simple. If the smell returns within a few days of an airing or a clean, the moisture is still feeding it, and no powder on earth will hold that line. Masking makes things worse as often as not, because a heavy scented product over a damp carpet just gives you musty-and-floral, which is somehow harder to sit in a room with than plain musty.
How do you get rid of it for good?
Find the water first. Everything after that is wasted effort until the source is off.
Start outside and underneath, not with the carpet. Check the airbricks are clear and open – rod them through, and clear back whatever has buried them outside. Get the external ground level back down below the damp-proof course where some helpful previous work has raised it. And go looking for the dull, ordinary leaks: a slow weep under the kitchen sink, a bath waste that’s been dripping into the void for a year, and a washing-machine tail that never seated right.
Get a proper damp reading taken if the cause isn’t obvious. A meter run across the floor and up the skirtings will tell you fast whether you’re dealing with damp coming up through the structure or condensation you’re making inside the flat, and those two want opposite fixes.
Then dry the place out. A dehumidifier run properly for a week or two, doors open and air moving, draws moisture out of the structure that a single afternoon with a machine never could. You can’t clean a wet floor dry. Give it the time it asks for, too – a subfloor that’s been damp for a couple of years doesn’t give the water back over a weekend.
Lift a corner before you spend a penny
Before you pay anyone for anything, lift a corner of the carpet in the worst spot and look. The state of the underlay and the board or slab beneath it decides everything that follows. Sound subfloor with damp only in the pile from an old spill, source now fixed – that carpet cleans up and holds. Black-spotted felt underlay over a tide-marked board – you’re into replacement, and no clever cleaning changes that verdict.
When is the carpet past saving?
When the smell has baked into the backing.
If the mould has worked down into the jute backing of the carpet itself, or into felt underlay that’s been wet for months, cleaning the surface is throwing good money after bad. The contamination lives in the structure of the materials now, and the honest answer is to lift the lot and start again over a subfloor that’s been dried out first. I’ve watched landlords pay for three deodorising cleans in a year on a flat that needed one new underlay and an afternoon with a builder outside.
Once the source is dealt with, keeping the smell away is mostly a matter of air. Don’t block the airbricks, ever, for anything. Crack a window or a trickle vent in the rooms that get steamy. A ground-floor flat that gets a through-draught now and then rarely smells of much at all.
The smell test that tells you it’s done
Here’s how you know you’ve won. Shut the flat up for two or three days with no sprays and no plug-ins, then walk in cold off the street. Neutral air means the damp is beaten and the carpet is clean for good. That cellar note back in the hall means water is still getting in somewhere and you’ve more work to do. Stop blaming the carpet and go back to the floor.
The patio in Peckham came up in the spring. The new carpet went down over dry boards, and it’s been quiet ever since.
