The Untouchables: Shielding Glass, Cladding and Live Services on Occupied Refurbishment Blasts

Abrasive blasting is indiscriminate. The nozzle does not know that a sealed unit is due to be retained, that a composite panel costs four figures, or that the conduit beneath it carries the building's fire alarm. On refurbishment projects -- particularly those in occupied or partially live buildings -- the difference between a clean substrate and an insurance claim is often a roll of tape applied properly, and a survey that found the things worth protecting.

Before Any Tape Comes Out: The Protection Survey

Protection begins with a walk-round, not a shopping list. The survey should cover the full elevation and the immediate surroundings: glazing and frames, gaskets and intumescent seals, composite cladding and rainscreen panels, sensors, cameras, pipework, cable trays, vents and neighbouring finishes. On urban sites, it should extend to parked vehicles, landscaping and street furniture within the likely blast shadow.

Record existing condition with dated photographs. A scratch noted before work starts is a baseline; the same scratch found afterwards is an argument. Establish early who owns the protection -- principal contractor, blasting subcontractor or a specialist masking contractor -- and put it in writing. The principle of prevention under CDM 2015 is not satisfied by a verbal assurance that someone will "keep an eye on" a retained façade.

The survey should also identify what cannot be protected by tape alone. A live sensor may need temporary removal by a competent person. A sealed window may need rigid boarding rather than a polythene wrap. A composite panel may need ventilation to avoid trapped moisture. These decisions belong in the method statement, not at the nozzle.

Materials and Methods: What Actually Withstands the Blast

Not all masking is equal. Low-tack tapes are appropriate for seals and finished frames; foil tapes may suit hotter local conditions; purpose-made masking films and rigid boards are available for glazing. Heavy-duty polythene has a place, but a single layer will not survive direct abrasive impact, and bin bags are not blast protection.

For glazing, the usual sequence is a foam or low-tack edge seal, a heavy polythene sheet taped and overlapped, and a rigid board where the pane is close to the work or irreplaceable. For composite cladding, avoid tight wraps that trap moisture; use breathable temporary protection and check fixings and panel joints after removal. For services, isolate and lock off where possible, cap open ends, bag and label. Sensors and cameras should be removed by the building's competent person or shielded in a rigid box with foam packing.

Gaffer tape is not a masking material. It leaves residue, can lift coatings and is difficult to remove cleanly from powder-coated aluminium. Reused masking contaminated with grit is worse than none. The specification should name the products, the number of layers and the inspection interval -- and the operatives should have enough of them.

Sign-Off Before the Nozzle Opens

Protection is only as good as the person who checks it. A pre-blast checklist -- glazing, cladding, seals, services, adjacent finishes, access routes -- should be completed by the blasting supervisor and countersigned by the principal contractor or client representative. Photograph the protected elevations. Include the protection regime in the permit to work and brief it at the toolbox talk.

A second pair of eyes matters. The person who applied the tape has already decided it is adequate. A short walk-round with someone who did not install it will find the gap at the head of the window, the unsealed service penetration or the polythene lap facing the wind. Re-check after storms, after scaffold alterations and at the start of each shift.

After the Blast: Inspection and Handover

Removal is part of the job. Protection should come off in a controlled way, without dragging grit across the very surfaces it was meant to protect. Inspect glass for pitting and etching, cladding for embedded abrasive, seals for cuts and frames for coating damage. Check that services are still isolated, that caps are intact and that nothing has been left inside a duct.

Record the post-blast condition against the survey photographs. Clean adjacent surfaces and remove tape residue with a suitable solvent. A defect found on day one is a snag; the same defect found at handover is a dispute. The protection record -- survey, specification, sign-off and inspection -- is the evidence that the works were managed, not merely completed.

Shortcuts That Become Claims

Most protection failures are predictable: the survey skipped because the job was "straightforward"; gaffer tape used because it was in the van; one layer of polythene where two were needed; window gaps left unsealed; blasting upwind of open windows; services left live because isolation was someone else's responsibility; no photographs because the site was busy. Each is a small saving on the day and a large cost on the claim.

On occupied refurbishments, the blast shadow is part of the risk assessment. Wind-blown abrasive finds open windows, ventilation intakes and freshly cleaned cars. A simple wind-direction check and a stop-work trigger can prevent a conversation with the insurer that no one wants to have.

Protection is not an overhead to be trimmed. It is the insurance you control, applied before the first pot is pressurised.