Why the smell comes back after a death in a flat

This is the part that catches people out, and it tends to surface after a first attempt at cleaning. The unit was cleaned. For about a week it seemed fine. Now it is back, and nobody can work out where it is coming from.

The explanation is simple, and once you know it, the failed attempts make sense.

The smell is not in the air. It is in the room

It is natural to treat an odour as something floating in the air, because that is where you meet it. But the air in a flat changes constantly. If the smell were only in the air, opening the windows would end it permanently.

What actually happens is that the material released during decomposition is absorbed by anything porous nearby, and then released slowly, for weeks. The usual holders are the mattress and bedding, timber, plaster and unsealed concrete, grout and the gaps at the skirting, soft furnishings and curtains, and the air conditioning, which will happily circulate it back out into a room you have just cleaned.

You are not smelling the air. You are smelling what the room absorbed, being released back into the air.

Why airing out and air freshener stop working

Both work on the air. The air is the one part of the problem that was going to clear on its own anyway.

Fragrance sits on top of the odour rather than removing it, so for a few days a room can smell of something else. When the fragrance fades, the source has not gone anywhere, and the smell returns to a home where somebody had already started to move on. That second return is worse than the first, because by then people have stopped expecting it.

Why painting over it does not hold

Paint over a wall that has absorbed odour seals it in for a short while. It is not a barrier built for that job, and if the substrate underneath is saturated the smell comes through it. Painting is a finishing step, not a treatment. Doing it too early usually means doing it twice.

What treating it at source means

• Find what absorbed it. That means looking under and behind things, not just at surfaces. It is often not where the smell seems strongest.
• Decide honestly what can be saved. Some materials cannot be treated to a standard worth paying for. You are told which, and why, before anything is removed.
• Remove what cannot be saved, and dispose of it through the proper waste stream.
• Treat what remains, at the material, rather than misting the air above it.
• Then deal with the air, which by that point is the easy part.

Done in that order it does not come back. Done in the other order it always does.

If the smell is coming from a neighbour’s unit

Odour does not respect a party wall. It travels through service shafts, ceiling voids and gaps around pipework, which is why the unit that smells is sometimes not the unit with the problem.

You can call and ask what your options are even when it is not your home. Knowing what the situation probably is, and who would normally arrange the work, is usually the thing people are missing.

How to tell whether it has actually gone

Close the unit up. No open windows, no fan, no air conditioning, for a full day, ideally through the warmest part of it. Then walk in from outside.

A room that has been ventilated continuously will pass a sniff test it has not earned. Shutting it up and coming back with a fresh nose is the honest version of the test.

If you want the whole sequence from the first call onwards, it is set out on What happens now, and the odour work itself sits under trauma and biohazard remediation.