How Do You Sign Off a Builders Clean Before a Cat B Office Handover?

You do not sign it off before the air conditioning has been commissioned. That is the whole article, and everything below is the argument for it.

The pattern is the same on every Cat B fit-out I have worked on in fifteen years. The main contractor is chasing practical completion, the client’s project manager wants a walk round on the Thursday, and the cleaning contractor is asked to have the floor sparkling by Wednesday night. Then the mechanical subcontractor runs the fan coil units up to full speed on the Friday for air balancing, and eleven weeks of construction dust comes out of the ceiling void and settles across 8,000 square feet of new desking.

Everybody blames the cleaners. The cleaners were there on Wednesday and the floor was immaculate on Wednesday.

What is the difference between a builders clean and a sparkle clean?

Three stages, and most fit-out programmes budget for two of them.

The first clean, sometimes called the rough clean or the builders clean proper, happens when the wet trades are finished and before decoration and floor finishes go down. It is heavy work: debris removal, plaster and screed residue, adhesive spots, silicone off glass, wet vacuuming of the slab or the raised floor panels. Nobody photographs this stage and nobody appreciates it, which is a shame, because a floor that gets a proper first clean needs a third less time at the end.

The second clean sits after the finishing trades and before commissioning. Cores, WCs, tea points, ironmongery, the top faces of everything.

The sparkle is the final pass. Glass both faces, all horizontal surfaces, floor finish machined or buffed as specified, ironmongery polished, then the floor is closed. The word “sparkle” has become a bit of a con in this trade, because it gets sold as a distinct high-value service when most of what it contains is a second clean done properly, with better lighting and more time. If you are being quoted a large number for a sparkle on a floor that never had a first clean, you are paying twice for the same soil.

Where does the money go?

Glass and edges. Not open floor. On a typical Paddington Basin floorplate with a full-height glazed perimeter and internal glazed offices, the glazing is somewhere near two-thirds of the labour hours, and the recessed detail – shadow gaps, skirting reveals, the underside of raised floor cut edges around trunking – takes most of the rest. Open carpet is quick. It is the last thing to worry about and the first thing everyone looks at.

Why does the floor look filthy again the morning after commissioning?

Because the ceiling void was never in anybody’s scope.

Above the tiles on a Cat B floor you have cable tray, containment, fan coil units, flexible ductwork, sprinkler pipework and the sound attenuation. All of it was installed over months by trades cutting plasterboard, drilling concrete, and dropping fixings. The void is a shelf. It holds cement dust, gypsum fines, cable sheathing swarf, insulation fibres, and the fine grey material that settles out of a construction environment and behaves like talc.

The tiles go in. The floor gets cleaned. The void stays as it is, and everybody forgets it exists because they cannot see it.

Then commissioning happens. Fan coil units run up, air is balanced through the grilles, and the void goes from static to moving air. On a plenum ceiling, where the void itself is the return air path, the effect is dramatic. Dust that has sat undisturbed since March comes down through the supply diffusers in a fine grey film across the meeting room tables, the monitor screens and the carpet under the perimeter. It comes back down.

I have seen a floor off Sheldon Square go from a signed sparkle sheet to visibly soiled in the six hours it took to balance the system. The client walked in on Monday convinced they had been sold a clean that never happened.

What should be done above the ceiling, and when?

Void cleaning before the tiles are laid in, as a scheduled item with its own line in the programme.

Vacuum the tray tops and the containment with a filtered vacuum rather than blowing anything through with compressed air, which relocates the problem into the next bay. Wipe the top surfaces of the fan coil unit casings. Clear the drip trays and the condensate pans of debris, which matters for a reason beyond cleanliness, since a fixing screw sitting in a pan will block a drain and put water through a new ceiling tile in August.

If the tiles are already in and commissioning has not run, lifting a percentage of them for spot cleaning of the worst areas costs a fraction of cleaning a whole finished floor twice. Ask for that. Most main contractors will agree to it once you show them the alternative.

When should the protective film come off the glazing?

Earlier than it does. Almost always earlier than it does.

Protective film on glass, and on the powder-coated aluminium of frames and reveals, is applied at the factory or on delivery and is designed as short-term protection. Most manufacturers specify removal inside 30 to 90 days. What happens on a slow-running fit-out is that the film goes on in November, the programme slips twice, and by the time anyone touches it the glass has had five months of direct sun through a south-facing elevation.

Ultraviolet cures the adhesive. The film goes brittle, tears into strips instead of peeling in a sheet, and leaves a continuous adhesive residue bonded to the surface. On glass that is recoverable with solvent and patience and a lot of hours. On coated glass and on polyester powder-coated frames it is a different problem, because the solvents that shift cured acrylic adhesive will also attack the coating, and a blade that removes residue from float glass will scratch a soft coat or a self-cleaning surface permanently.

The cost differential is not subtle. Peeling film inside the window is minutes per pane. Recovering baked film is an hour a pane with two people, and on a floor with 140 panes that is a five-figure conversation nobody budgeted for.

Walk the elevation at week eight and pull a test corner. If it tears rather than stretches, get the whole lot off that fortnight and re-protect with something appropriate if the works demand it.

What about the floor protection?

Same principle, different failure. Hardboard and correx taped down over new stone or timber traps moisture and grit underneath, and the tape adhesive on a vinyl or a resin floor cures in exactly the way film does. Lift a section every few weeks and look. If there is standing grit under the boards it is being ground in by every trolley wheel that crosses it, and the sparkle clean will not fix a scored floor. It comes back down through the void and it works its way under the boards, and both of those are somebody’s programme decision rather than a cleaning failure.

How do you inspect it so the snags stick?

With a torch, at a grazing angle, in the dark.

Overhead LED at full output flattens everything and hides film residue, smears on glass and dust on horizontal edges. The inspection that finds things is done with the lights down and a hand torch held nearly parallel to the surface, which throws every mark into relief. It is how you find the tide mark on the underside of a worktop nosing at nine in the evening.

Do it before the furniture lands. Once 90 desks and 400 chairs are in, the underside of every horizontal surface is inaccessible, the delivery crew has walked cardboard fibre across the whole floor, and the snag list you produce is a list of things nobody can now reach. Furniture delivery after commissioning, and after the post-commissioning clean, is the sequence that works. It is also the sequence that project programmes ignore most often, because furniture lead times drive everything else.

What should be on the sheet?

Room by room, not floor by floor, with a defect logged against a location reference that matches the drawing. Photograph each one with something in frame for scale. A snag reading “glass smeared” against a whole elevation will be argued about for a fortnight. A snag reading “adhesive residue, pane G14, lower right quadrant” gets fixed on Tuesday.

Who is holding the risk between the last clean and handover?

The main contractor, until practical completion, and that is precisely why the sequence matters commercially.

Before PC, the floor is a construction site under the contractor’s control, and anything that soils it is theirs to put right. After PC, possession passes to the client and the cost of a second clean lands on the tenant’s own budget. So a sign-off given on the Thursday before Friday commissioning transfers a problem worth thousands from one party to another, and the person asking for that signature usually knows it.

What we tell contractors who want the sheet signed on the Friday

No, and we will come back on Tuesday.

This costs me goodwill with the exact people who book us, which is main contractors and fit-out project managers, and I have had the conversation go badly more than once. It is still the right answer. Sign the second clean, hold the sparkle sign-off until commissioning is complete and the grilles have been wiped and the supply diffusers checked, then walk it with a torch and close it out.

The dust in that void has been there since the first fix. It comes back down when the air moves, and it will come back down on your handover day if you let the programme decide the order.

Book the return visit into the programme at tender stage and nobody has to argue about it in week thirty.