A carpet in a ten-year-old flat and the same carpet in a Victorian terrace age at completely different rates, and it has nothing to do with how often anyone hoovers. The old house is working against you. A period building is a leaky thing by design — air moves through it constantly, up through the floor, down the chimney, in around the windows — and all that moving air carries dust and soot with it. Your carpet is the finest filter in the room.
Nobody walks in that much dirt on their shoes. Most of what greys a period carpet was already in the house, or came straight through its fabric.
Why do carpets in period homes get dirty faster than in a new-build?
Because a new-build is sealed and an old house is not.
A modern flat is built to keep air where it’s put. Membranes under the floor, insulation in the walls, tight double glazing, a solid concrete slab instead of a timber void, and no chimney at all — the air inside is more or less the air you let in through a window or a vent. Very little moves on its own.
A period terrace is the opposite in every particular. The ground floor is usually suspended timber — floorboards laid over joists over an open, ventilated void that’s kept deliberately draughty by airbricks in the outside wall, so the timber doesn’t rot. Above that sit single-glazed sash windows that never quite seal, open or blocked-off chimney flues, and walls of lath, horsehair plaster and soft lime mortar that shed a fine dust of their own as they age. The house is full of routes for air to travel, and air is never still in it.
What does it mean to say an old house “breathes”?
Builders use the phrase literally. Warm air inside the house rises and escapes at the top — up the chimney, into the loft, out through every gap at ceiling level. As it leaves, it has to be replaced, so the house pulls cooler air in low down: through the airbricks and up between the gaps in the floorboards. That slow, constant current from bottom to top is the stack effect, and in a tall period house with an open flue it runs all day whether you feel a draught or not. Every bit of that incoming air has come past old brick and the fine grey soil of the underfloor void, and it carries a load of that with it. The house breathes in at the floor and out at the roof, and the carpet is sitting right in the intake.
Why do dark lines appear along the skirting boards and under the doors?
This is the one that brings people to the phone, usually convinced the cleaner did a bad job or the wall is damp.
You clean a period carpet, it comes up beautifully, and within a few months there’s a sharp dark line — grey to black, pencil-thin to a couple of centimetres wide — tracing the skirting board around the edge of the room and running under the door across the threshold. In some rooms it draws a faint grid on the floor that mirrors the boards underneath. It’s called filtration soiling, and it’s one of the most misread marks in the trade.
Here’s what’s happening. All that air the house is drawing through itself has to get from the floor void into the room, and the easiest way through is the gap where the carpet meets the skirting, or the slot under a door. Air takes the path of least resistance, gets forced through the pile at exactly those edges, and the carpet does what a filter does — it strains the fine black particulate out of the air and holds onto it. The middle of the room barely sees this, because air isn’t being pushed down through it. The edges get the entire filtered load, concentrated into a line that maps the airflow precisely. That’s why it’s so unnervingly sharp. A tracked-in stain is random; a filtration line is a straight, deliberate-looking band, because it’s drawn by airflow rather than by feet.
The particulate itself makes it worse. Filtration soot is extraordinarily fine, and it’s greasy — carbon particles from traffic and old flues carry an oily film that makes them cling to fibre and resist ordinary cleaning. It works its way deep into the base of the pile and grips. This is not a wipe-off job.
Is that black line dirt, or is the carpet damaged?
Dirt — every time. The fibre is perfectly sound; there’s simply a concentrated deposit of very fine airborne soot filtered out along the line where the air comes through. The catch is that the house never stops supplying it. Clean the line out and the building starts drawing the next one the same day. The line is the visible end of a process that’s still running, which is why it always comes back.
I recall pulling a set of these out of a four-storey Victorian on Elgin Crescent in Notting Hill. The owners had done a beautiful, careful restoration — original fireplaces reopened, floorboards sanded back through most of the house — and one back room kept its carpet. Within a few months of every clean, a black line came up along all four skirtings, crisp as if someone had drawn it with a marker. They were sure it was rising damp in the walls. What it actually was: every open flue and every gap in the house pulling London through that one carpeted room and dropping the soot at the edges.
How much of the black is actually soot from the chimney?
A great deal of it, and the chimney doesn’t need to be in use.
An open fire is an obvious source — burn anything and you produce soot, some of which settles into the nearest soft furnishings. But the flue is a problem even cold. A Victorian chimney has spent a century lined with the soot of coal and wood fires, and it’s a tall vertical shaft open to a room at the bottom. When the house pulls air downward through it — a downdraught on a gusty day, or the stack effect reversing — it brings fine soot and ashy dust down out of that lining and into the room, where it drifts onto the carpet. The soot that blackens a filtration line is very often flue soot rather than street soot, which is why the lines in a chimney-heavy old house run darker than the traffic alone would explain.
Do unused fireplaces still let soot in?
Yes, if they’ve been left open or blocked without ventilation. A decorative fireplace that’s simply been bricked up at the front but still has an open flue above is a direct pipe from a soot-lined shaft into the room. Even a properly closed chimney breast can let fine dust through gaps in old plaster. A chimney cap on the pot outside, paired with a small vent or a chimney balloon inside, cuts the downdraught right down — and a flue that’s actually swept, rather than just abandoned, drops far less of its lining into the room.
Does bringing back the original floorboards make it better or worse?
Worse, for dust. A decade of interiors magazines has this exactly backwards.
Stripping a period floor back to bare sanded boards is the single most popular thing anyone does to one of these houses, and it looks superb. It’s also a sieve. Every gap between every board — and old boards shrink, so the gaps are real — is an open slot letting the underfloor draught, and everything it’s carrying, straight up into the room to settle on the floor and the shelves. A fitted carpet over a decent sealed underlay does the opposite: it caps most of those gaps and filters the air that does get through. For sheer dust control, a carpet with good underlay is the cleaner floor in a Victorian terrace, whatever the fashion says — the bare boards everyone covets are a large part of why these houses feel like they can never be got properly clean.
What about the sash windows?
They leak, and on a London street that means diesel. Original box sashes let air past the frame and between the sliding sashes even when they’re shut, and if the house faces a trafficked road, that gap is a direct feed for the fine black particulate that traffic throws out. The carpet in a bay window is usually the first to grey for exactly this reason. Draught-proofing the sashes with discreet brushes and seals — which a good joiner can do without spoiling the windows — cuts the incoming grime a surprising amount, and keeps the original glass.
What can actually be done about it?
You manage it. You don’t cure it, short of gutting the house of the character you presumably bought it for.
The useful moves are all about slowing the airflow through the carpet. Draught-strip the doors and the sashes. Seal the worst of the floorboard gaps, or lay a good sealed underlay that does the filtering for you. Cap and vent the unused flues, or fit chimney balloons, and have the working ones swept. Vacuum the room edges more often than the middle, since that’s where the load lands. None of it stops the house breathing, but all of it reduces what the carpet has to filter.
Can a professional clean the black edge lines out?
Usually most of the way, with the right treatment — filtration soiling needs a strong solvent-based pre-spray worked directly into the line, then proper agitation and extraction to break the greasy soot off the fibre and flush it out. Done well, a line that looked permanent comes up dramatically. Done on an old, heavily set line, some shadow can remain, because the soot has been ground into the base of the pile for years. And it will start to return, because nothing about the treatment changes the building.
The black line at the skirting is really a clock. Once you know what it is, you can read roughly how many months it’s been since the last clean by how far it’s darkened back in.