I clean carpets for a living, so it costs me money to say this: some carpets are past cleaning, and the straight answer is to replace them rather than take your money for a wash that was never going to work. Most people get the call backwards. They tear out carpets that had years left in them, and they keep paying to clean carpets that were finished a decade ago.
Knowing which is which isn’t complicated once you know what you’re looking at. It just isn’t the thing people assume.
How do you tell a dirty carpet from a worn-out one?
Dirt and wear look similar from the sofa and are nothing alike underfoot.
Dirt lodges on and around the fibre. It’s grease, dust, spills, the grey film that builds up over a winter of shoes and central heating — and all of it, in principle, lifts. Wear is different in kind. Wear is damage to the fibre itself, and no cleaning method touches it because there’s nothing there to lift; the fibre is simply worn away or worn out.
The clearest case is the grey traffic lane down a hall or in front of a sofa. People assume it’s ingrained dirt and book clean after clean to get rid of it. Sometimes it is dirt. Often it’s abrasion.
Why do traffic lanes stay grey no matter how often you clean them?
Grit is the culprit. Every shoe carries in fine, hard particles — road grit and the mineral dust that gets everywhere in a city — and in the spots where people walk, that grit gets ground into the pile underfoot thousands of times. It works like sandpaper. It scratches and splits the tips of the fibres, and roughened, split fibre scatters light instead of reflecting it cleanly, so the lane reads as dull and grey even when it’s perfectly clean. That grey is scratched fibre, not dirt.
Here’s the test, and it’s the only one that matters: have the carpet cleaned once, properly, by hot-water extraction. If the lane comes back up to match the rest of the room, it was dirt — that’s a clean, and cleaning was the right call. If it dries and the lane is still grey, the fibre is worn, and it will be grey after the next clean and the one after that. At that point you’re paying to wash sandpaper. Once a traffic lane has survived a proper extraction clean and stayed grey, booking another clean is money down the drain — and any cleaner who tells you the next visit will fix it is either mistaken or hoping you are.
I had this out with a tenant on Mill Lane in West Hampstead a couple of years back. She’d had the hall runner-line cleaned three times by three different firms, each one promising the grey would come up, and it never did. The carpet was a builder-grade synthetic that had done eight years of daily traffic, and the tips were shredded — you could feel the difference, rough where the lane was and soft everywhere else. No clean was ever going to help. I told her to stop paying people like me and put the money toward a new floor. That’s a replace, not a clean, and no amount of my equipment changes it.
Matting is the other wear you can’t clean out. Pile that’s been crushed flat for years, in a doorway or under a castor, sometimes lifts with cleaning and grooming and sometimes has set permanently, the fibres bent and locked over. When it’s permanent, it stays flat no matter what you do to it. You can usually tell by touch. Run a hand across a worn lane and it feels coarse and thin under the fingers, nothing like the plush give of the parts nobody walks on.
What damage can cleaning never reverse?
A fair amount. Knowing which is which saves you the cost of a clean that can’t work.
Burns and melts come first. Synthetic carpet is essentially plastic, and heat fuses it — a dropped iron, a stray ember, a pair of hair straighteners left face-down on the floor will melt the fibre into a hard, discoloured knot. The fibre structure is destroyed at that spot. Nothing dissolves it back into carpet. A small burn can sometimes be patched with a plug of matching fibre cut from a cupboard offcut, but it’s patched, never cleaned.
Bleach is the next. Splash bleach, a strong toilet cleaner, or some acne creams on a carpet and it strips the dye straight out, leaving the fibre intact but colourless — usually orange or white. The fibre is fine. The colour is gone, and cleaning can’t put it back. A specialist can occasionally re-dye a spot, but it’s fiddly and rarely worth the cost against replacement.
Then there’s physical damage — cuts, tears, seams that have unravelled, edges frayed away from a threshold. And in wool carpets, moth: the larvae graze the pile down to the backing in patches, and once the wool’s eaten there’s nothing to clean, only bare threadbare gaps where the pile used to be.
Why a melted fibre is permanent
Because melting changes the fibre itself. The plastic has flowed and reset as a solid lump with none of the original structure, and cleaning only ever removes things resting on the fibre — it can’t rebuild fibre that’s been cooked into something else.
When has a smell soaked in too deep to clean out?
Pet urine is the usual answer, and it’s the one people most often try to clean their way out of long after that’s stopped being possible.
A single accident, dealt with quickly, cleans out fine. The trouble is the ones that don’t get dealt with — the cat that’s been going in the same corner for months, the puppy that was never quite house-trained. Urine doesn’t stay in the pile. It soaks through the backing into the underlay, and from there into the floorboards or the concrete screed underneath, carrying salts and bacteria down with it. Those salts are hygroscopic — they pull moisture out of the air — so every humid day reactivates them and the smell comes back, sharp, from a carpet you cleaned last week. Shop-bought deodorisers only make it worse. They mask the smell for a day or two, which buys the contamination more time to spread while you assume it’s handled.
Why cleaning the carpet doesn’t fix a urine smell
You can clean and deodorise the pile perfectly and still have the smell, because by then the source has moved below the pile — into the underlay and the subfloor, beneath anything a carpet clean reaches. Sorting it properly usually means lifting the carpet to replace the contaminated underlay and seal the subfloor with a barrier primer before new carpet goes down. That’s a replace with building work under it, not a clean.
Is cleaning an old carpet worth it, or throwing good money after bad?
Depends entirely on what’s left to work with.
A carpet has a working life. A domestic synthetic gives you maybe eight to twelve years before the pile loses its spring; a good wool carpet, looked after, goes considerably longer. The tell is in how it recovers. Press your thumb into a healthy pile and it springs back. Press into a carpet that’s reached the end and the dent stays — the fibre has lost its resilience for good, and a carpet with no spring left mats flat wherever it’s walked and never looks fresh however well it’s cleaned. It just looks like a clean tired carpet.
Now the economics. A single professional clean costs a fraction of a new carpet, which is exactly why cleaning a carpet that still has life in it is good value — you’re buying years for a small outlay. The sum flips when the carpet is worn out. Three cleans in two years on a matted, grey-laned carpet that comes up no better each time adds up to a real chunk of what a new carpet and underlay would have cost, and you’ve nothing to show for it but a slightly-less-dirty version of the same floor. Spend it once on a replacement instead. Landlords feel this most sharply, because the maths tempts them the wrong way — another quick clean between tenancies is cheaper this month than a re-carpet, so the same worn hallway gets washed tenancy after tenancy until a checkout dispute finally forces the replacement that should have happened three tenants ago.
How long should a carpet actually last?
In a normal household, a mid-range synthetic in a bedroom might see fifteen years; the same carpet in a hall or on a stair, taking the whole home’s foot traffic, can be worn through in six or seven. Location does most of the ageing. A carpet wears out unevenly, always fastest where people walk, which is why you so often replace a whole room because of one ruined runner-line down the middle of it.
If you do replace it, does the underlay need to go too?
Usually, yes — and it’s the bit people skip to save money, then regret.
Underlay wears out too. Old foam underlay breaks down into a fine crumb; you feel it as a loss of cushioning and hear it as a faint crunch underfoot. Felt underlay flattens and hardens. Fitting a fresh carpet over dead, crumbling underlay is a false economy — the new carpet loses its comfort fast and wears quicker on a base that no longer supports it. And if the reason you’re replacing is contamination — urine, a long-standing damp patch — the underlay has to go regardless, because it’s holding the very thing you’re trying to be rid of.
Can you ever reuse the old underlay?
The one time you can reasonably keep it is when it’s genuinely sound: a good rubber-crumb underlay only a few years old, dry and springy, under a carpet you’re changing for looks rather than wear. Lift a corner and check before you assume.
When the fitters pull up an old carpet, the state of the underlay usually settles the argument on its own. Foam that’s turned to grey powder along the traffic lines, a smell that rises the moment it’s disturbed — by then nobody’s asking whether it needs replacing.