Fourteen tiles. That was the honest damage assessment on an 840 square metre floor in Farringdon, and the facilities manager had a quote in front of him for cleaning all 3,360 of them, twice a year, for three years.

I did not write that quote, but I have written ones like it, and so has every contractor reading this. The modular floor is the one product in our sector that was designed from the outset to make most of our recurring work unnecessary, and the trade has spent thirty years quietly declining to mention it.

What proportion of an office floor is ever the problem?

Between three and eight per cent, in my experience of surveying them, and it is always the same three to eight per cent.

Soiling in a commercial interior follows footfall, and footfall follows a small number of fixed routes. The tiles inside the entrance where the matting run ends. The lift lobby, where everybody stands still and pivots. The tea point, particularly the metre in front of the machine where somebody turns with a full cup. The printer bay. Under task chairs, where a castor spins in one place eight hours a day. The threshold of every meeting room door.

Everything else on a modern floor plate is close to the condition it was laid in. The middle of an open-plan bay in a Croydon office building, behind the desks, gets walked on perhaps twice a week by a cleaner, and paying tile for tile to clean it on a quarterly cycle buys you nothing measurable.

The six places tiles die

Walk any floor with a floor plan and a marker and you will mark the same spots. Entrance run-off, lift lobby, tea point, printer bay, chair castor positions, meeting room thresholds. Add a seventh in buildings with an external smoking area, which is the twenty tiles between the fire door and the lift. I have never surveyed a London office where the damage sat anywhere except in that list, and I have surveyed a great many.

What can cleaning not put back?

This is the part that decides the argument, and it comes down to the difference between soil and damage.

Encapsulation, low-moisture methods and hot water extraction all remove soil. Soil is loose or bonded particulate and greasy film sitting on and in the yarn, and a competent clean takes most of it out. What no clean touches is physical change to the fibre or the backing. Crushed pile in a lift lobby, where years of standing loads have permanently deformed the yarn, cleans up and stays flat. Abraded tips under a castor, where the fibre has been ground away, look no better wet than dry. Bleach marks from a cleaner’s spray bottle are absence of colour. Caramelised sugar in a tea point tile that has been cooked by the afternoon sun for two years is a permanent tint. Bitumen backing that has delaminated because a leak sat under it stays curled.

So the twice-yearly whole-floor clean is asked to solve two problems, one of which it can solve everywhere and one of which it cannot solve anywhere. Meanwhile the areas that look bad are the areas with damage, so the floor looks unchanged three days after a clean and the facilities manager concludes that cleaning does not work.

There is a related waste that nobody costs. A clean puts moisture, however little, into a floor that is 95 per cent sound, and every clean moves a small amount of soil from the pile surface into the backing rather than out of the building. Do that eight times over four years on tiles that did not need it and you have aged the whole floor to save the appearance of the seven per cent that was ruined anyway.

Crush and soil look identical in a photograph

They do not look identical under a torch. Hold a light across the pile at a low angle. Soiled pile is dark and stands up. Crushed pile catches the light differently because the yarn is lying over, and it shows a flat grey sheen regardless of how dirty it is. Two minutes with a torch before you accept any quote, including mine, will tell you which of the two you are being sold a solution to.

Where do replacement tiles come from if nobody kept spares?

Three sources, in order of preference.

Attic stock first. Any decent fit-out specifies five to ten per cent over, and in about half the buildings I survey there are boxes of it in a basement store, behind the Christmas decorations, forgotten by two generations of facilities staff. Ask the landlord’s managing agent as well as your own team, because tiles often stay with the building rather than the tenant.

Second, the manufacturer. Commercial tile ranges have long production lives, and a current range in a current colourway can be ordered in a box of twenty for a sum that will surprise anyone used to fit-out pricing. Expect a dye lot difference, which matters less than people fear because you are placing them in specific positions rather than across a whole bay.

Third, harvesting. Lift good tiles from beneath the server cabinet, inside the stationery store, under fixed storage walls and behind reception joinery, and put those into the damaged positions. Then put the damaged tiles where they were harvested from, under things nobody will ever see. Tile for tile, this is the cheapest fix in the building, and it costs materials of nothing.

The server room is a warehouse

The floor under a comms cabinet has been in darkness and under static load since the day it was laid. Its colour is the original colour, which makes it an imperfect match for a ten-year-old floor that has faded, so lift those tiles a month ahead and leave them stacked face-up in the open-plan area to catch up. Half the tricks in this trade are about light, and that one costs a stack of boxes and four weeks of patience.

Why does a swapped tile sometimes stand out?

Three reasons, and all of them are avoidable if whoever does the work knows what they are looking at.

Pile direction is the first. Every tile carries an arrow on the back, and the floor was laid either monolithic, with every arrow the same way, or quarter-turned, with each tile rotated ninety degrees from its neighbour. Put a monolithic tile in the wrong orientation and it reads as a different colour from two metres away, because pile direction changes how light returns from the surface. Check the arrows on the tiles you are lifting before they leave the floor.

The second is age. A new tile among worn ones is brighter, fuller and cleaner, which is why swapping only the damaged tiles in a lift lobby sometimes produces a lobby that looks patchy in a new way. The fix is to spread the change: put new tiles into low-traffic positions and move their previous occupants into the lobby.

The third is the tackifier. Carpet tiles are fixed with a pressure-sensitive adhesive that stays tacky rather than curing, and a tile bedded onto fresh tackifier sits a fraction proud of its neighbours for a few days. That settles. A tile laid onto old, dusty tackifier without a fresh coat lifts at a corner within a month and gets kicked.

What the work takes

A tile lifter, a knife, a tin of tackifier and a notebook. Twenty tiles in a lift lobby is comfortably an afternoon for one person, no drying time, no equipment in the corridor, and the floor is in use the same evening. Against that, a whole-floor encapsulation clean of the same building means night access, a team, a supervisor and an invoice with four figures on it.

When should you pay for the whole floor after all?

There are real cases, and I take those jobs gladly.

Uniform soiling is the honest one. Where an entire floor plate has gone a flat grey and the change is even across the bays, that is soil, it is everywhere, and cleaning is the correct treatment. Buildings with poor entrance matting get there in about eighteen months. Fix the matting at the same time or you will be back.

Then there are contractual reasons. A lease or a schedule of dilapidations that specifies professional cleaning with documentation means you clean and you keep the invoice, whatever the floor looks like. A building being handed back at the end of a term is a different exercise from a building in use. Pre-sale, pre-inspection and pre-visit cleans are appearance jobs and I will do them without argument.

And there are floors where swapping is off the table: discontinued ranges with no attic stock, complex patterned or plank layouts where a single replacement breaks the design, and floors where the tiles are so far gone that a swap programme would mean replacing a third of them, at which point you are re-carpeting in instalments and should price a proper replacement instead.

What I would put in the contract

A targeted clean of the traffic areas two or three times a year, a full clean once every second or third year, and a standing allowance for tile replacement with the attic stock audited and recorded on a plan. Tile for tile that is a smaller annual number than most offices are paying now, and the floor looks better, because the tiles that make a floor look tired get removed rather than washed.

One caveat I put in writing every time: get the swap done by somebody who fits floors, or by a cleaning contractor who has lifted tiles before. A badly bedded tile in a lift lobby is a trip hazard and it will be the first thing the insurer photographs.

Most contractors will quote you the other way round because square metres are easier to sell than judgement. I have lost two accounts in Hounslow and one in Canary Wharf by putting the version above in writing, and the Farringdon floor is still on fourteen swapped tiles and one clean a year.