Is the asbestos cement roof on your garage or outbuilding leaking, crumbling at the edges or covered in moss? You have three realistic options: seal and coat the sheets where they are, repair local damage, or remove and replace them. This guide covers when each option may suit, what the HSE says, and the asbestos roof coating system we make at our Ulverston factory for roofs that are still sound.
Before choosing a product, read the HSE's free Asbestos essentials guidance. The full Kingfisher Building Products range, plus free technical advice, is at kingfisheruk.com or on 01229 869100.
Safety first
- Asbestos cement (AC) roofs are always fragile and cannot bear a person's weight. Work from the ground or from a suitable platform. Never stand on the sheets.
- Never sand or rub down the surface. HSE sheet a16 covers painting AC sheets.
- Sealing and coating is only for roofs that are essentially sound. Before any work starts, have a competent person (such as an experienced roofing contractor or a structural engineer) inspect the sheets and the supporting structure.
- Sheets that are damaged or decayed beyond practical repair need replacing.
- The HSE explains which asbestos jobs are licensed, notifiable non-licensed or non-licensed work on its non-licensed work page. Encapsulating asbestos materials that are in good condition and maintaining AC roof sheeting are both listed there as non-licensed work.
Encapsulation vs repair vs removal
| Option | When it may suit | What is involved | Check first |
|---|---|---|---|
| Encapsulate (seal + coat) | The sheets and supporting structure are sound and in reasonable condition | Bio-Wash, damp-down cleaning, Parabond for minor cracks, 1 coat of Asbestos Sealer & Primer, 2 coats of Asbestos Roof Coating | Inspection by a competent person. HSE lists encapsulation of asbestos materials in good condition as non-licensed work |
| Repair local damage | Minor cracks or holes, e.g. around fixings | Parabond for cracks up to 3 mm; Fibreseal and Scrim Mesh for bigger cracks or holes | HSE sheet a13 |
| Remove / replace | Sheets damaged or decayed beyond practical repair, or the structure needs work | Small-scale removal with the sheets kept intact (HSE sheet a14); larger jobs need a full risk assessment and plan of work | If the AC breaks up and creates significant dust, the job becomes notifiable non-licensed work. Costs can be considerable |
What not to do
- Don't stand or walk on the sheets. The HSE says AC roofs are always fragile.
- Never sand or rub down the surface (HSE a16).
- No DIY high-pressure jetting. The HSE says it should only be used in exceptional circumstances, by a specialist contractor who collects the slurry (HSE a12).
- Don't dry-brush moss. Mist the roof damp first, then bag the debris as asbestos waste.
- Don't coat a roof that hasn't been inspected. Coatings are only for roofs that are essentially sound.
- Don't apply to damp surfaces or in wet weather.
- Don't seal over gas-fired exhaust vents (HSE a12).
The products, in the order they are used
Our asbestos roof range includes a fibre-encapsulating coating, a sealer and primer, a garage roof kit, Bio-Wash roof cleaner and Parabond sealant. Everything is made for asbestos cement sheets that are still sound.
Asbestos Garage Roof Coating Kit
The Asbestos Garage Roof Coating Kit is a solvent-free system for cleaning, consolidating, waterproofing and improving the look of corrugated asbestos cement roof sheets. Each kit contains:
- 10 L Asbestos Roof Coating
- 5 L ready-mixed biocidal wash
- 5 L Asbestos Sealer Primer
- a 380 ml tube of Parabond sealant
It covers approximately 22 m², roughly a single garage. Apply by brush or spray, and not on damp surfaces or in wet weather.
Step 1: clean with Bio-Wash Roof Cleaner
Bio-Wash Roof Cleaner is a concentrated biocide that kills moss, mould, lichens and algae, and helps stop moss growing back under a new coating. Dilute it 1 part to 4 parts water: one 5 L container makes 25 L and treats up to 125 m².
On asbestos cement:
- Spray it on with a low-pressure garden sprayer.
- Leave it for seven days.
- Mist the roof with water and scrape the dead growth into bags for disposal as asbestos waste.
No dry-brushing and no DIY pressure washing.
Step 2: consolidate with Asbestos Roof Sealer & Primer
Asbestos Roof Sealer & Primer is a translucent, water-based acrylic that soaks into the surface of old asbestos cement sheets to bind, seal and consolidate it.
- As a primer: one coat before the coating.
- As a stand-alone exterior sealer: two coats.
- Application: brush, or low-pressure (non-atomising) spray. It can also be sprayed on the underside of a roof where light dusting is seen.
- Coverage: 4-6 m² per litre.
Step 3: waterproof and encapsulate with Asbestos Roof Coating
As Asbestos Roof Coating cures, the polymer bonds to the sheet and encapsulates the fibres, so weathering and abrasion don't expose them. It also restores waterproofing and gives a satin finish.
- Coats: two over the primer, generally 6-8 hours apart.
- Application: brush, or high-pressure airless sprayer.
- Coverage: 4-6 m² per litre per coat, so a 10 L pail covers approximately 50 m².
HSE guidance referred to in this post
- Asbestos essentials
- a12: Cleaning weathered asbestos cement roofing
- a13: Repairing damaged asbestos cement
- a14: Removing small amounts of asbestos cement
- a16: Painting asbestos cement
- Non-licensed work with asbestos
Kingfisher Building Products Ltd, Cooper Lane, Ulverston, Cumbria LA12 9RA. Tel 01229 869100. www.kingfisheruk.com
Kingfisher Building Products Limited (Companies House SC249720) is a UK manufacturer of sealants, coatings and damp-proofing products, based at Cooper Lane, Ulverston, Cumbria LA12 9RA. Tel 01229 869100. Kingfisher Building Products is an independent company and is not connected with Kingfisher plc or B&Q.