Problem: Asbestos roof maintenance
The use of Asbestos Cement (AC) was banned in new buildings in 1990 due to growing concerns about the health hazards posed by asbestos fibre release, especially during construction and maintenance. However existing buildings fitted with AC roofing materials including the familiar corrugated roof sheets and cladding can continue to provide useful and safe service for many years providing they are correctly maintained and managed.
How do I know if my roof/cladding is asbestos?
Every property owner has a legal duty to identify the presence of known asbestos containing materials (ACMs) and owners/occupiers of commercial premises must maintain an asbestos register. In most cases an independent survey will be carried out by a BOHS trained surveyor who will take samples for analysis to identify all ACMs, including the roof/cladding. Asbestos Cement corrugated sheets have quite a distinctive appearance and therefore analysis will almost invariably confirm it to be AC.
- Degradation from U.V light, rain, wind and the freeze/ thaw cycle eventually renders AC sheets porous, allowing dampness to ingress into the building.
- This moisture ingress can trigger corrosion in the roof structure which is typically steel framed. Long term this may cause structural instability.
- AC sheets may typically contain only around 10% asbestos fibre but it is important to note that severe weather induced erosion will eventually expose those fibres.
- Older AC roof sheets are prone to accumulating moss and lichen growth, which in-extremis leads to cold spots and condensation, especially on the steel purlins.
- In older buildings, structural settlement over time can cause hairline cracks in the sheets.
- The original sheet fixings are often badly corroded and replacement can be impractical.
Solution: Asbestos roof maintenance
Asbestos in its solid or settled form, is relatively safe. However, when disturbed by damage or poor working practice, it can release a cloud of fibrous particles, which if handled without appropriate safety equipment and work-wear can result in respiratory distress. As a general rule AC sheets are best sealed or encapsulated to contain fibre release.
- Pre-treat roof with "Bio Wash" (kills moss, green mould & lichens).
Liberally spray the entire roof surface with Kingfisher "Bio Wash" using a low pressure sprayer (as for garden weed-killer) and leave for seven days to activate. This effectively sanitises the roof surface by killing the obvious areas of growth as well as the hidden spores buried deep in the substrate and overlap joints.
- Clean Roof (remove debris)
Thoroughly damp the roof by mist spraying with water (suppresses release of harmful fibres) and brush/ scrape the dead moss and other surface dirt and laitance into bags for disposal as AC waste. Alternatively for larger areas the "closed box" pressure washing method described in HSE doc A12 can be used but the waste sludge and water run-off have to be collected in the gutters and down pipe. This involves diverting all run off into one down pipe usually temporarily modified on site to divert the water into a mobile water filtration system. Allow to dry. Note: DO NOT pressure wash asbestos with a lance attachment as this may result in the uncontrolled release of potentially harmful asbestos fibres. There is a highly informative two page document covering this on the HSE web site, reference number A12 which can easily be downloaded for your further reference.
- Repair Roof
General: Sealers and coatings should only be applied to essentially "sound" roofs so a pre- inspection of the roof structure and surface condition should always be undertaken by a competent person (e.g. experienced roofing contractor or structural engineer) before commencing works. This will determine whether the supporting steel/timbers are in need of repair and identify any cladding/roof sheets which are damaged or decayed beyond practical repair and therefore need complete replacement. In addition this inspection will typically inform the competent person's choice of access equipment to be used for safe execution of the works.
Minor Repairs: Any minor cracks or holes, especially around fixings can be filled with "Kingfisher 1 for All" hybrid polymer sealant. Cracks of up to 3mm can be successfully filled by applying a bead of "1 for All" along the crack and then pressing / smearing it firmly into the damaged area. We recommend wearing disposable latex gloves for this task as the hybrid polymer, whilst neutral in its formulation is very highly adhesive! "1 for all" is fully over-paintable once cured but try to avoid applying primer to it. Note: Kingfisher "Multi-task" wipes are formulated to quickly remove "1 for all" from skin and tools before it cures.
Larger Repairs: Bigger cracks or holes can be bridged with "Kingfisher Fibreseal" – a thixotropic fibre reinforced roofing compound & "Kingfisher Scrim Mesh". Apply one coat of "Fibreseal" to the affected area and bed the fine mesh into the "Fibreseal", then leave to cure. Once cured apply a second coat over the mesh. Avoid applying the "Asbestos Primer" to this repair and leave for a minimum of 2 days before applying "Kolourseal" or "Asbestos Roof Coating".
- Prime Roof
Apply one coat of Kingfisher "Asbestos Sealer & Primer" by brush or spray. DO NOT over apply. Brush out any runs which may occur. The material should have soaked into the surface after approximately 20 minutes. Drying time will vary depending on the surface porosity and ambient temperature, but normally 4 – 8 hours should be allowed for each coat to fully dry. However, it is better to apply subsequent coats of "Kolourseal" or "Asbestos Roof Coating" whilst the primer still has a slight "tackiness" as this aids adhesion.
- Application of Waterproof Coating
Apply 2 x coats of "Asbestos Roof Coating" by brush or airless spray. If applying by brush use a high quality masonry paint brush, working in broad even strokes, taking care not to over-apply. Pay close attention to sheet edges and corners ensuring that the coating is worked well into all crevices and joints.
If applying by high pressure spray, we recommend a typical GRACO 4900 or 5900 series airless sprayer with the pressure set at 2500 psi and fitted with a 517 nozzle tip blade (17 thou) for optimum performance. Ensure that roof-lights and vents etc. are protected from over-spray and take precautions to avoid spray drift contamination of vehicle finishes in the vicinity.
Apply only in dry conditions to a dry surface, with no rain expected for at least 24 hours post application. As with all water based treatments, please be aware that you need to plan any exterior works to allow sufficient drying time for the product to cure before the evening dew point, especially in the shorter days of winter. On a roof surface warmed by the summer sun "Kingfisher Asbestos Roof Coating" will dry in under an hour, permitting two coats to be applied in one day whereas in winter initial cure can be 4 hours so only one coat is possible.
IMPORTANT! Asbestos Cement roofs can be very fragile and must only be accessed with caution using the correct weight spreading crawler boards, harnessing, access platforms etc. We are primarily coatings manufacturers NOT Health & Safety advisors and as such we do not offer definitive guidance on "working at height" or "working with asbestos", so we recommend that you consult a competent person or Health & Safety professional for guidance on all aspects (PPE, best practice etc.) before commencing any works.
Products to Remedy the Problem
Bio-Wash Moss Remover, is the maintenance professional’s choice for controlling troublesome moss growth on exterior hard surfaces like tarmac driveways, block pavers, sandstone paving slabs, concrete slabs, walls and much more.
Asbestos Roof Sealer and Primer is a brush or spray applied, translucent solution formulated to bind, seal and consolidate the surface of old, friable asbestos roof sheets, encapsulating harmful dust and fibres. It also improves the moisture resilience of the surface. Non-hazardous, suitable as both interior and exterior asbestos sealer.