Heritage Building Silica Dust — Repointing, Stone Repair and RCS Control on Listed Fabric

Heritage stone cleaning is a wet discipline, and V-TUF covers it separately. This page is about the other half of heritage work — the dry half. Raking out joints, repointing, cutting indents, stone repair, plaster and render removal. That is where respirable crystalline silica comes from on a listed building, and it is governed by COSHH 2002 exactly as it is on a new-build site.

Looking for softwash, biocides and low-pressure cleaning? Heritage stone and listed building cleaning · Need the dust classes explained? L, M and H compared

Where the silica comes from in heritage work

Heritage contractors often think of silica as a demolition and groundworks problem. In practice the highest-exposure operations on a listed building are the routine repair tasks, carried out repeatedly across a long programme:

Raking out and cutting out joints before repointing — mechanical raking with a disc or grinder is the single highest RCS generator on most heritage jobs
Removing hard cement pointing from historic fabric, common on buildings repointed unsympathetically in the twentieth century
Cutting and dressing indents and stone repairs on site, including banker work in a site workshop or under a temporary shelter
Removing failed render, stucco and hard plaster back to sound substrate
Drilling for helical ties, cramps, resin anchors and structural repair
Clean-down and enclosure strip-out at the end of a phase, where settled dust is disturbed again

The exposure limit is the same as anywhere else: 0.1 mg/m³ for respirable crystalline silica averaged over 8 hours. What differs on heritage work is how much of the shift is spent on those operations, often in confined or scaffolded spaces with restricted airflow.

Why heritage dust is harder than new-build dust

On a construction site the first-choice control for RCS is water suppression. On historic fabric that is frequently the control you cannot use.

Saturating porous limestone and sandstone, wetting lime mortar during repointing, mobilising soluble salts through the stone, and introducing water into fabric that then faces a frost cycle are all recognised conservation risks. Where the conservation method statement restricts wetting, the burden shifts onto on-tool extraction, enclosure and RPE to achieve the same control.

That has three practical consequences worth stating plainly in a method statement:

On-tool extraction stops being optional. If water is restricted, extraction at source is doing the work that suppression would otherwise do, and the machine needs to be specified and maintained accordingly — correct shroud, adequate airflow, filter cleaning that keeps working across a full shift.
Airflow matters more than capacity. Heritage work is often at height on scaffold, through long hose runs, in enclosures. Airflow at the tool is what captures the dust; a large drum that cannot maintain suction at the end of 10 metres of hose is the wrong machine.
The dust control may itself need consent. Enclosures, sheeting, temporary shelters and fixings into historic fabric can require listed building consent or scheduled monument consent in their own right. Plan the dust control at the same time as the repair method, not after.

Which class — and why the stone name is not the answer

Dust class is not set by the name of the stone. It is set by how much respirable crystalline silica the operation actually generates, which depends on the material, the tool, the duration and the controls in place. RCS is treated as a carcinogen, which is why materials known to produce heavy RCS exposure sit at H-Class.

V-TUF publishes a position on the heritage materials where the exposure is established and documented:

Material	Where	Published position
Magnesian limestone	York and the Vale of York, Tadcaster, Ripon, Durham	H-Class
Bath stone (Jurassic oolite)	Bath, Bradford on Avon, Corsham, Frome	H-Class
Firebrick and cristobalite	Stoke-on-Trent bottle ovens and kiln structures	H-Class — mandatory for demolition
Mourne granite	Newry and South Down	H-Class

Heritage stone is not limited to those four, and the absence of a stone from that table is not a position that M-Class is adequate. Portland limestone, Cotswold limestone, Yorkstone, red sandstone, flint and granite are all in widespread historic use across the UK and all need assessing rather than assuming.

For a stone not listed above

Establish the silica content. Quarry or supplier declaration, or the safety data sheet for a replacement or repair material. Sandstones are quartz-based and generally warrant close attention.
Establish what the operation does. Mechanical raking out and grinding generate RCS at a completely different order to hand-raking with a quirk or plugging chisel. Hand tools remain a legitimate control on heritage work and are sometimes required by the conservation method statement anyway.
Establish the controls available. Whether wetting is permitted, whether the work is enclosed, duration across the programme, and who else is in the space — including the public, on an occupied or visited building.
Where you cannot establish the first two, specify H-Class. On a long heritage programme the machine cost is immaterial against a stopped site or a health claim.

Consent, method statements and the public

Two consent regimes run alongside the COSHH duty and neither replaces it.

Listed building and scheduled monument consent govern what you may do to the fabric — and, as above, can extend to the enclosures and fixings used for dust control. Unauthorised works to a listed building are a criminal offence under the Planning (Listed Buildings and Conservation Areas) Act 1990.

COSHH 2002 governs the exposure of the people doing the work, and is not discharged by having consent. A conservation-compliant method that exposes an operative to RCS above the limit is a COSHH failure regardless of how sympathetic it is to the building.

Heritage work also happens disproportionately on buildings the public can reach — cathedrals, museums, visitor attractions, town centre frontages, occupied churches. Where the work is in or adjacent to public space, containment is protecting visitors as well as operatives.

COSHH Regulations 2002 · CDM 2015 · HSE EH40 Workplace Exposure Limits

Equipment for heritage dry work

Specification follows the assessment, not the other way round. In practice heritage programmes tend to need on-tool extraction that holds airflow at the end of a hose run, and formats that work on scaffold.

Where the assessment lands at H-Class

The GRINDEX1100LPS is the compact H-Class option — 25L, automatic reverse-flow filter cleaning triggered by differential pressure, tool-start PTO, 200 m³/h, in 110 V site-safe and 240 V. For scaffold and at-height work without a mains supply at the point of work, the RUCKVAC HSV cordless backpack gives H14 sealed filtration in a format an operative can carry up a lift.

H-Class dust extraction — full specification and range

Where the assessment lands at M-Class

The GRINDEX1100LP covers general construction and workshop dust at 20L and 200 m³/h with Longopac continuous bagging, and the MIGHTY HSV adds an autostart PTO for grinders and cut-off saws.

M-Class dust extraction — full specification and range

Continuous bagging is worth a specific mention on heritage sites: it lets an operative change a full bag without opening the machine and re-releasing captured dust, which matters when the alternative is doing that on a scaffold lift beside a cathedral wall.

Trade accounts for heritage and conservation contractors

Tell us the stone, the operation and whether your method statement permits wetting, and we will confirm the class and the machine that fits. UK warehouse, UK technical support, spares held for every machine in current production.

Telephone: 01522 787978. Mention heritage or conservation at first contact.