Cleaning a London Flat After a Summer of Open Windows and Traffic Dust

Second floor on Junction Road in Archway, sash windows onto the A1, and by the end of August the white-painted sills had gone the colour of weak tea. The tenant had wiped them weekly with a dry duster all summer and could not understand why they kept coming back grey within two days. They were not coming back. She had been moving the same film around the reveal since June, thinning it in the middle and building it up at the edges, which is what a dry cloth does to an oily deposit. That’s traffic.

What is the grey-black film on London window sills made of?

Less exhaust soot than people assume, and more of everything else.

Brake pads shed iron and copper particles every time a bus slows for the lights. Tyres abrade against the road and throw off rubber and bitumen fragments. Road surface itself wears away. These non-exhaust sources now account for a large share of the particulate matter in London air, and they have not fallen the way tailpipe emissions have since ULEZ went citywide – engines got cleaner, brakes did not. Add summer construction dust, pollen, and the coarse grit that a passing lorry lifts off the tarmac, and you have the mix that settles on your sill.

The important property of that mix is that a good part of it is oily. Tyre and bitumen particles, diesel residue, and cooking aerosols from your own kitchen bind the mineral dust into something closer to a thin grease than to household fluff. It sticks. It resists dry removal. It picks up new dust faster than a clean surface does, so the problem accelerates through August.

Why a dry cloth makes it worse

Dry dusting a greasy film shears it. Some lifts, most redistributes, and a fine layer gets pressed into the paint’s surface texture where the next wipe cannot reach it. Two months of that on a gloss sill leaves a dull grey ghost that survives washing and needs a mild abrasive cream or a repaint. You want detergent from the first pass – warm water with a drop of washing-up liquid does most of it, and a proper alkaline cleaner does the rest.

Which surfaces are holding the most, and which do people clean anyway?

People clean the sill, because they can see it. The sill is holding perhaps two per cent of what came through the window.

Fabric holds the rest. Curtains hanging directly in the airflow of an open sash on a main road are the single largest reservoir in the flat – a pair of unlined cottons from a front room on Mile End Road will run the rinse water grey. Upholstery next, then rugs and carpet, then the mattress, then the top of every horizontal surface above eye level where nobody looks: picture rails, wardrobe tops, the flat top of a door frame, the pelmet, light fittings.

Then there is the airing cupboard problem in reverse: books. Open shelving in a front room facing a bus route collects a startling amount along the top edge of the pages, and it is the reason a flat can smell faintly of road in October even after the surfaces have been done.

The mattress and the sofa

Summer means less bedding, more skin, windows open all night, and a mattress sitting three feet from a road. It takes the lot. A HEPA-filtered vacuum over the whole surface, seams included, using the upholstery head and slow overlapping passes rather than quick strokes – slow matters more than suction here, because the airflow needs time to lift particles out of the fibre. Ten minutes for a double. Flip and repeat. If you have never done this and you live on a red route, the filter will tell you a story you would rather not hear.

Sofas the same, cushions out, back and underside included. Where the fabric is washable and the covers zip off, wash them at 40 and stop there. Whatever anyone tells you, a summer’s worth of traffic dust in a sofa does not require an extraction machine and £180. It requires an unhurried vacuum, twice.

How do you strip a summer’s accumulation without redistributing it?

Order of operations, and the order is not negotiable.

Top down. Anything you disturb falls, so the ceiling rose, the picture rail, the wardrobe tops, and the curtain heading come first, before you have cleaned a single thing at knee height. Dry to wet, too: vacuum the loose material off with a brush attachment before any water touches the surface, because water plus loose traffic dust equals a grey slurry that you then wipe into the paintwork.

Ventilate the wrong way for once. Windows shut on the road side, extractor fan running, and open something on the quiet side of the building if you have one. Cleaning day is the one day you do not want a fresh supply of what you are removing.

Take the curtains down first thing and get them into the machine or into a bag for the launderette before you start on anything else, so they are not hanging in the room catching what you disturb. Same with rugs – rolled and out into the hall.

Working the hard surfaces

Warm detergent solution, two buckets or two cloths, and change the water when it goes grey, which will be sooner than you expect. Reveal, sill, frame, then the wall below the window, which is filthier than the rest of the room and almost never touched. On matt emulsion go gently and test in a corner, because oily traffic film on matt paint sometimes cannot be washed off without burnishing the finish, and the honest answer in a rented flat on Streatham High Road is often a tin of paint rather than four hours of scrubbing.

What about the windows, blinds and the vents you have never opened?

Glass last, after everything else, or you will do it twice.

Venetian blinds in a road-facing room are a genuine misery and the fastest method is the least dignified: unhook them, lay them flat in the bath, warm detergent, sponge each slat, rinse with the shower head, hang over the rail to drip. An hour for a wide window, and better than any in-situ method involving tongs and patience. Fabric roller blinds mostly cannot be washed – vacuum them through a nylon stocking and accept the result.

The window itself needs the frame and the runners done before the glass. Sash channels and casement drainage slots pack with grit over a summer and hold water afterwards, which is where the black spotting on the bottom rail starts.

The filters and grilles nobody remembers

Trickle vents along the top of modern window frames clog solid. Pop the internal cover, wash it, brush the slot out, and hold a torch up there because most people have never looked. Extractor fan grilles in bathrooms and kitchens the same. If the flat has mechanical ventilation with heat recovery – common in the newer blocks around Brentford and along the river – the unit takes filters that need replacing at least annually, and in a road-facing flat, more often. Nobody in the building tends to know where the unit is. It is usually in the utility cupboard above the boiler.

Can you keep next summer’s film thinner without shutting the windows?

Partly, and here is where I will talk myself out of work.

If your flat faces a busy road, the single most effective thing you can do costs nothing: keep the road-side windows shut between about seven and ten in the morning and again through the evening peak, and ventilate hard in the middle of the day and late at night when traffic volume drops. That’s traffic – it comes in waves, and the waves are predictable to within about half an hour.

Second, fit fine insect mesh to the sashes you use most. It catches the coarse fraction, cuts the visible grit substantially, and costs perhaps £15 a window from a hardware shop on any high street.

Third, and this is the part my invoicing would rather I skipped: do not book an annual deep clean for this. Wash your curtains twice a summer, vacuum the mattress and sofa properly once a month with a HEPA machine, and wipe the reveals with detergent rather than a dry duster, and you will not need us for it. Where people should spend money is on a decent air purifier with a real HEPA filter for the bedroom of a front-facing flat – it does more for the dust and for what it carries than any cleaning I can sell you. Book the deep clean for the kitchen and the bathroom, where the work needs a professional and equipment.

What about the doormat and the shoes

Roughly a third of what settles inside a ground or first-floor London flat walked in on somebody’s feet. Brake dust and road grit sit in the tread of every shoe that comes off Whitechapel Road, and a coir mat inside the door does close to nothing – the fibres are too coarse to hold fine particles and they release them again as you cross. A ribbed rubber-and-textile barrier mat of at least 1.2 metres, so each foot lands on it twice, takes a serious bite out of the load. Shoes off at the door takes more. In a two-bed flat off Barons Court Road we cut the visible dust on the hall skirting by something like half after the tenants adopted both, with no change to anything else.

Vacuum the mat itself weekly, from underneath as well. A saturated barrier mat is a distribution device.

The tenant on Junction Road washed her curtains in September and the rinse water came out the colour of the sills. That’s traffic. She keeps the front sash shut until half past nine now.