Asbestos cement (AC) roofs were widely installed on commercial, industrial and agricultural buildings across Ireland and Northern Ireland between the 1950s and late 1990s. Most are now 30–70 years old, weathered, leaking and producing fibre run-off — but full removal typically costs three to five times more than encapsulation and takes the building out of use for weeks. This guide explains exactly how to waterproof an asbestos roof without removal, what the regulations in Ireland require, and how to specify a system that lasts 20 years or more.
Why Waterproof Instead of Remove?
Removing an asbestos cement roof is asbestos work under the Safety, Health and Welfare at Work (Exposure to Asbestos) Regulations 2006–2025. It must be survey-led and risk-assessed, it requires an HSA permit (from 30 December 2025), and it involves careful stripping of the sheets, controlled hazardous waste disposal, and in most cases a new replacement roof on top. Encapsulation — coating the existing roof with a liquid waterproofing system — is still asbestos-related work that must be planned, risk-assessed and notified to the HSA where required, but it leaves the sheets undisturbed, avoids the disruption of stripping, and extends the service life of the asset by 20 years or more.
For owners of warehouses, factories, agricultural buildings, distribution centres and workshops, encapsulation is usually the most practical decision. The roof stays in place and the building stays open. Companies in Northern Ireland may also be able to claim Land Remediation Relief against the cost — see our guide on Land Remediation Relief for asbestos works (Northern Ireland companies only) for the tax detail.
Is It Legal to Coat an Asbestos Roof?
Yes. Asbestos cement sheets in good enough condition are often best left in place and managed, and encapsulation is a recognised way to do that. In the Republic of Ireland the work falls under the Safety, Health and Welfare at Work (Exposure to Asbestos) Regulations 2006–2025, enforced by the Health and Safety Authority (HSA). From 30 December 2025 asbestos work needs an HSA permit, which means notifying the HSA with a plan of work and risk assessment at least 10 days before work starts. In Northern Ireland the Control of Asbestos Regulations (Northern Ireland) 2012 apply, enforced by HSENI. Spray-applied encapsulation seals the weathered surface and stops fibre release rather than disturbing the sheets — provided exposure is controlled and the operatives hold recognised asbestos awareness training.
Suitability Survey: What to Check First
Not every asbestos cement roof is a candidate for encapsulation. A proper suitability survey looks at structural integrity, sheet condition, moss and lichen cover, previous repairs, and the substrate's ability to accept a coating. The pass/fail criteria Duratite uses on every survey are summarised below.
| Factor | Acceptable | Reject |
|---|---|---|
| Sheet breakage | Isolated, <5% of area, repairable | Widespread fracture, >15% area |
| Delamination | Surface weathering only | Deep lamination, crumbling |
| Structural purlins | Sound, dry, no rot | Rusted through or rotten |
| Moss / biological growth | Removable with biocide wash | Root penetration into sheet |
| Previous bitumen repairs | Localised, can be over-coated | Full roof bitumen — poor adhesion |
| Ridge and flashings | Original AC or zinc, serviceable | Missing or unstable |
Core Pull Tests
On borderline roofs the surveyor will do adhesion pull tests (ISO 4624) to confirm the primer bonds to the aged cement surface. A pull result above 0.6 MPa is generally considered acceptable for a liquid applied system.
The Waterproofing Process Step by Step
Duratite uses a seven-stage process that has been refined over hundreds of asbestos roof projects. Every stage matters — skip one and the warranty falls over.
1. RAMS and Site Set-Up
Site-specific risk assessment and method statement, HSA notification where required, fibre exposure controls, edge protection, MEWP access or roof ladders, controlled waste route for wash water.
2. Biocide Clean and Controlled Wash
A fungicidal/biocide wash is applied by low-pressure lance (never high-pressure jet — that releases fibres). Wash water is captured and disposed of as controlled waste where required.
3. Repair and GacoPatch
Cracked sheets, fixing holes and previous repairs are reinforced with GacoPatch and fibreglass scrim. Ridge caps and flashings are re-bedded as needed.
4. GacoPrime Primer
A penetrating primer is rolled or sprayed across the entire roof area to seal the porous cement substrate and lock fibres in place.
5. Two Coats of GacoFlex S42
The main waterproofing layer — GacoFlex S42 is a fibre-reinforced silicone applied in two cross-hatched coats at a total dry film thickness typically around 0.6–0.8 mm.
6. Final Inspection and Wet Film Records
Wet-film thickness readings are logged on a project map so that coverage can be evidenced for the warranty.
7. Warranty Registration and Handover
Duratite registers a 20-year warranty on GacoFlex S42 installations, issues the O&M document, and hands over the site.
Get Free Advice or Book a Survey
Duratite's technical team provides free site assessments and fixed-price quotations across Ireland and Northern Ireland. No obligation.
Choosing the Right Coating System
Duratite installs three core Gaco systems for asbestos cement roofs. Selection depends on roof condition, expected service life, and budget. A quick comparison:
| System | Best For | Warranty | Relative Upfront Cost |
|---|---|---|---|
| GacoFlex S42 | Long-life, high-spec projects | 20 years | Mid-to-high — lowest per year |
| Gaco 127 Acrylic | Mid-life, budget-conscious | 10 years | Lowest |
| GacoFlex U92 Urethane | High-traffic or industrial zones | 15 years | Highest |
Most commercial clients choose GacoFlex S42 because the cost-per-year-of-protection is the lowest. For a full technical comparison see GacoFlex S42 vs 127 vs U92.
Typical Costs and Project Timeline
Every asbestos roof project is priced individually — roof size, access, condition and the chosen system all move the figure, so Duratite gives a fixed quote after a free site survey. Timelines run from three days for a small workshop up to six weeks for a large distribution warehouse. What drives the price is explained in our asbestos roof waterproofing cost guide.
Warranty, Compliance and Aftercare
Every Duratite installation is covered by a full product and workmanship warranty, registered to the building. Aftercare is straightforward: an annual visual inspection, clear debris from gutters, and check flashings after severe weather. Fully manufacturer-documented systems and teams with recognised asbestos awareness training mean the paperwork stands up to insurance and landlord scrutiny.
Common Mistakes to Avoid
The three most common reasons an asbestos roof coating fails early: high-pressure washing that disturbs fibres and damages sheets; skipping the primer stage to save cost; and applying coatings in unsuitable weather (below 5°C or during rain). A properly specified job avoids all three.