Asbestos Roof Waterproofing — Clarkes 24/7, Bristol
From failing roof to finished system
The Challenge
Asbestos cement is stable while its surface is intact. What the survey recorded in October 2025 was a surface losing that battle: weathering across all sheets, capillary weeping at the side and end laps, and fibre-binder erosion concentrated at the fastener heads. No airborne release had been reported — but continued exposure to rainwater, UV and freeze–thaw cycling would predictably accelerate sheet matrix breakdown, and over time increase the likelihood of fibre release.
The building is accessed daily by staff and visitors and bordered by active commercial neighbours. That geometry is exactly what makes conventional strip-and-dispose removal so unattractive: significant disruption, downtime, and an airborne-fibre risk imposed on third parties.
Project file
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The Solution — step by step
Why not simply remove it?
Stripping the roof would have meant a licensed contractor, containment, controlled disposal of every sheet, and a working building handed over to the programme — all to replace sheets that were still structurally sound. Encapsulation inverts the logic: it seals the material where it stands, locks the cement matrix in place, and shields it from the weathering that was breaking it down.
There is also a tax dimension. Encapsulating asbestos is not repair — in HMRC’s terms it is land remediation, and qualifying expenditure can attract Land Remediation Relief: a 150% corporation tax deduction. Duratite issued a formal Asbestos Land Remediation Works Report for this project as the technical basis for the owner’s claim, which is made by the owner’s accountants against their own tax position.
The system
A four-stage Gaco liquid-applied silicone system, supplied as one specification — each stage preparing for the next, nothing optional.
- GacoWash — substrate cleaner. Diluted 1:9 and applied by low-pressure sprayer, agitated with soft brushes, residues removed with controlled rinsing and wet-vac collection. No power washing — jetting weathered asbestos cement abrades the very surface being contained.
- Gaco SF42 — fibre-reinforced stripe coat. Applied as a stripe coat and seam seal to every side lap, end lap, ridge detail and fastener head. The fibre reinforcement within SF42 provides mechanical strength at these stress points without needing a separate woven fabric.
- GacoPatch — silicone putty filler. High-build silicone putty to larger holes, cracks, damaged fixings and voids — bringing the roof to a smooth, defect-free substrate before the field coats.
- GacoFlex S42 — two full field coats. Two complete coats of high-solids silicone across the entire roof area, applied at the specified wet film thickness for the 20-year warranty film build. 96.5% solids, solvent-free, UV-stable, ponding-water resistant.
The installation
This was a supply-only project in its purest form: Duratite Building Products specified the complete system, supplied every product and set the application and QA requirements — and Clarkes 24/7 Ltd’s own trained operatives carried out the works, briefed under a site-specific RAMS with asbestos awareness training held.
Fragile-roof discipline applied throughout: crawl boards, roof ladders and fall-arrest harnessing whenever the sheet surface was accessed before the cured coating was load-bearing, with edge protection maintained for the duration. Coating was scheduled around dry-weather windows and suspended in out-of-specification wind, rain or temperature, with overspray containment beside the neighbouring units and public access areas.
Film build is what a coating warranty stands on, so wet film thickness checks were taken regularly with calibrated comb gauges, ambient conditions were assessed daily, and product batch numbers were recorded for traceability. The patent-glazed rooflight runs were retained and worked around, keeping daylight in the unit.
The Outcome
The roof now sits under one fully monolithic silicone membrane bonded directly to the asbestos cement beneath. The deterioration recorded at survey — the weeping laps, the failing washers, the eroding fibre-binder — is arrested and sealed under reinforced silicone. Not a single sheet was disturbed, and the building and its neighbours worked normally throughout.
In April 2026 Duratite Building Products issued the 20-year manufacturer-backed material warranty, certificate WC2026-0031, against the documented QA record — and the Land Remediation Works Report gives the building owner the technical evidence base to claim the 150% Land Remediation Relief deduction on the qualifying works.
On the roof — the full picture
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Read the case studyHave a similar asbestos roof waterproofing project?
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