Run every tap and flush every loo before you do anything else, then open all the windows and go and have a coffee for twenty minutes. The smell in a long void isn’t dirt. It’s drain gas coming up through traps that have evaporated dry, and if you start cleaning without dealing with that you’ll spend the whole day chasing a smell you can’t find and blaming the carpet.
Voids are the strangest cleaning job there is. Nothing has happened in the flat and yet it’s in worse condition than a place four people have lived in.
Dust behaves differently, mould appears where nobody made steam, and the flat has developed a smell of its own that new tenants will notice in the first four seconds and never quite forget.
What actually goes wrong in a flat where nobody’s been?
Four things, and none of them are dirt in the ordinary sense.
Traps dry out. Every waste has a U-bend holding a plug of water that stops sewer gas coming back up, and in an unheated empty flat that water evaporates in eight to twelve weeks. Kitchen sink, basin, bath, shower, washing machine standpipe, and the one everyone forgets – the floor gully outside if there is one, and the overflow on a rarely used cloakroom basin.
Damp appears without anybody generating it. There’s no heating, no air movement, and whatever moisture is in the fabric of the building goes to the coldest surface available. In a north-facing bedroom of a solid-walled conversion that means a bloom of black spotting in the top corner and along the outside wall behind where the wardrobe stood. Nobody breathed it out. It came from the building.
Dust settles into a film rather than a layer. Six months of undisturbed settlement produces something fine and even and slightly greasy, and it doesn’t lift with a dry cloth the way a fortnight of dust does – it smears.
And insects. Dead flies on every south-facing windowsill, spider webs in ceiling corners, and in a ground-floor flat, silverfish in the bathroom.
The smell, specifically
Stale air in a sealed flat gets into soft surfaces. Carpet, underlay, curtains, any remaining upholstery, and the pile of the doormat.
It reads as musty rather than dirty and it’s the single thing most likely to lose you a viewing. Air alone doesn’t shift it once it’s in textile – you need airflow for days plus a proper hot water extraction on the carpets, and you need to do the extraction early enough that the flat dries fully before anyone moves in.
Booking the carpets for the morning before check-in is the classic void mistake. A damp carpet in an unheated flat in November is still damp four days later and now smells worse than it did.
What order should the work run in?
Ventilate and plumb first, dry second, clean third, and everything I said about high-to-low and floors-last applies once you get to the third stage.
Day one is not a cleaning day. Open everything, fill every trap, turn the heating on and leave it on at eighteen degrees, run the shower hot for five minutes, flush both loos twice. If the water’s been off at the stopcock, open it slowly and check under sinks afterwards – seals shrink in a dry system and I’ve come back to a puddle in a kitchen in Leyton because a compression joint under a basin had let go an hour after I turned the water on.
Then leave the flat with heating on and trickle vents open for two or three days if the schedule allows. That single measure does more than any product. Heat plus air movement drives the residual moisture out of plaster and soft furnishings, and it’s what makes the difference between a flat that smells fresh and one that smells cleaned.
Only then the actual clean, and it’s essentially a deep clean with a mould treatment and a heavier emphasis on soft furnishings than usual.
The heating question landlords argue about
Turning the heating on in an empty flat for a week costs perhaps twenty pounds and prevents most of what I’ve just described.
Voids get left cold because nobody wants to heat an empty property, and then eight hundred quid of mould remediation and carpet replacement happens in a flat that could have been kept at fifteen degrees on a timer for the price of a takeaway. The insurance angle matters too – unoccupied property endorsements frequently require a minimum temperature over winter, and if a pipe goes in a flat that was left cold in breach of that condition, the claim gets interesting.
Set a frost stat or a timer. Two hours morning and evening is enough.
How do you handle the mould, and is it your problem or the building’s?
Treat it and then work out where the moisture came from, in that order, because a tenant is moving in.
The treatment on surface mould on painted plaster is straightforward and specific. Don’t dry brush it – that aerosolises spores through the flat. Damp-wipe first with a fungicidal wash, leave the dwell time on the label rather than the one you’ve decided is enough, then wipe off, dry the surface, and if it’s marked the plaster underneath needs a stain block before repainting or it ghosts through emulsion within a fortnight.
Bleach on porous plaster is a half-measure. It kills what’s on the surface and takes the colour out of what’s underneath, which is why mould treated with bleach looks gone and comes back in the same shape in six weeks.
Where it came from is nearly always ventilation and cold surfaces rather than a leak, in a void. No leak produces a neat bloom in a top corner. But check anyway – look at the ceiling directly beneath any bathroom above, look under the bath, look at the wall by the soil stack, and photograph anything ambiguous before you touch it, because if it turns out to be a defect you’ve just cleaned off the evidence.
The bit that’s the landlord’s problem, not the cleaner’s
If the flat has no working extractor in the bathroom, or the kitchen extractor recirculates through a filter nobody’s changed, the mould will be back inside one winter and it will be the new tenants’ fault by then.
I say this on quotes now and it doesn’t always go down well. A void clean that removes visible mould without anybody fixing the airflow is a cosmetic job that hands a known problem to somebody who’ll be blamed for it, and I’ve watched the same corner of the same bedroom in a flat in Thornton Heath get treated three times across two tenancies.
Fifteen minutes with an extractor fan is cheaper than three treatments. It’s also the difference between a tenancy that renews and one that ends in a dispute.
What needs replacing rather than cleaning?
Filters, sealant, and sometimes the carpet, and being honest about the third one saves everybody a wasted day.
Any extractor filter, cooker hood filter or MVHR panel that’s sat for six months goes in the bin rather than through a sink. Silicone in a bathroom that’s been unused and cold often has mould growing inside the bead rather than on it, and no amount of scrubbing reaches that – it comes out with a blade, the surface gets cleaned and dried properly, and new sanitary-grade sealant goes in. That’s an hour and it transforms how a bathroom reads.
Carpet is the judgement call. If it’s ten years old, greyed, and smells after extraction and drying, extraction is money spent to postpone a decision. Tell the landlord straight, with a photograph of the pile parted, and let them decide. Underlay is usually the thing holding the smell, and there’s no cleaning underlay.
The kitchen appliances after a long void
Fridge and freezer doors should have been propped open when the flat was emptied and about half the time they weren’t. A sealed fridge left off for six months grows something specific and the seal absorbs it.
Bicarb, hot water, seal channel done with a soft brush, and then left open with a bowl of bicarb in it for a couple of days. If it still smells, it’s not going to stop, and a new tenant will open it once and mention it in their first email.
Washing machine gets a hot maintenance cycle empty, plus the drawer and the door seal, which will have mould in the fold at the bottom. Dishwasher the same. Both take an hour of elapsed time and no attention, so start them when you arrive.
What should be done in the last day before check-in?
Nothing wet. That’s the rule and I hold it firmly.
Carpets extracted at least three days out, in a heated flat, with air moving. Sealant done four days out so it’s fully cured and doesn’t photograph dark or feel tacky. Floors mopped the day before rather than the morning of. Anything that puts moisture into a flat which has spent six months learning to hold moisture wants time to leave again.
The day itself is the light pass and the checks. Fill every trap again, because if the flat’s been standing since the deep clean the traps in the rarely used wastes may already be low. Test every light. Run the extractor. Check the boiler pressure and that the hot water actually comes through. Open the windows for an hour and shut them before you go, and leave the heating on a low constant rather than off.
Then the check-in inventory, which in a void flat is worth doing with more photographs than usual – a flat that’s been empty has small defects nobody has been present to notice, and the tenant will find them in week one and be accused of causing them. Photograph the mould corner even after treatment. Photograph the carpet. Photograph the marks on the wall where the wardrobe stood.
Leave a window on the vent latch in every room and tell the incoming tenant why. They’ll close them all on day one anyway, but at least somebody said it.
