Can I Seal Cracked Asbestos Cement Cladding with Silicone Myself?

Sealing cracked asbestos cement cladding with silicone might seem like a simple weekend fix, but in New Zealand it carries real health risks and legal obligations you need to understand first. Whether you can do it yourself depends on the condition of the cladding, the extent of the damage, and how the work is classified under NZ regulations. Read on before you pick up a caulking gun.

What Is Asbestos Cement Cladding?

Asbestos cement (AC) cladding — sometimes called fibrolite or Super Six — was widely used on NZ homes built roughly between the 1940s and mid-1980s. It contains chrysotile (white) asbestos fibres bound into a cement matrix. When the material is intact and unpainted, the fibres are largely locked in place. When it is cracked, broken, sanded, drilled, or cut, fibres can become airborne — and that is where the danger lies.

Asbestos-related diseases such as mesothelioma and asbestosis are caused by inhaling these microscopic fibres. There is no safe level of exposure.

Is Sealing It Yourself Legal in New Zealand?

This is where many homeowners are surprised. Under the Health and Safety at Work (Asbestos) Regulations 2016, any work that disturbs asbestos — including cutting, grinding, or abrading — is classified as either Class A or Class B asbestos removal work, both of which require a licensed removalist.

However, carefully applying silicone sealant to a crack without disturbing the surrounding material is generally considered encapsulation rather than removal or disturbance, and may fall outside the licensed-work requirements — provided you do not sand, scrape, brush, or otherwise abrade the surface in the process.

The key rules to understand:

• Do not sand, wire-brush, or abrade the cladding surface at any point — this releases fibres and immediately makes the work notifiable licensed-removalist territory.
• Do not break or cut any sheets to access the crack.
• If the crack is friable (crumbling, powdery, or the edges are loose), the material is considered friable asbestos, and you must not touch it — call a licensed asbestos removalist immediately.
• If you are unsure whether the cladding contains asbestos, have it tested by an accredited laboratory before doing anything.

Always confirm your specific situation with WorkSafe NZ or a licensed asbestos assessor before proceeding.

When Silicone Sealing May Be Acceptable

If the crack is hairline or narrow, the edges are firm and non-friable, and you can apply sealant without disturbing the surface, careful encapsulation may be a reasonable short-term measure. Here is how to approach it as safely as possible:

Before You Start

• Confirm the material contains asbestos — if your home was built before 1990, assume it does until tested.
• Check the crack carefully. If edges are crumbling or powdery, stop and call a professional.
• Wear a P2 (half-face) respirator — not a dust mask — disposable gloves, and old clothing you can bag and dispose of.
• Work on a still, dry day to minimise fibre drift.
• Dampen the crack lightly with a fine water mist to suppress any loose dust before touching it.

Applying the Sealant

• Use a good-quality paintable silicone or polyurethane sealant suitable for exterior use. Products are available from Bunnings or Mitre 10 — check the manufacturer's datasheet for compatibility with painted cement surfaces.
• Apply carefully with a caulking gun, pressing sealant gently into the crack without scraping or abrading the edges.
• Smooth with a gloved finger or a damp tool — do not use abrasive pads.
• Once cured, consider applying a penetrating encapsulant paint over the area. Resene and Dulux both offer exterior primers suitable for use over asbestos cement — check with their technical teams for the right product.

After the Work

• Double-bag any used gloves, rags, or disposable clothing in heavy-duty plastic bags, seal them, and label them as asbestos waste.
• Dispose of at a council-approved facility — contact your local council for guidance, as asbestos waste cannot go in general rubbish.
• Wash your hands and face thoroughly.

Is Silicone a Long-Term Solution?

No. Sealing a crack is a temporary measure only. Asbestos cement cladding that is cracking is likely weathering and becoming more brittle over time. The BRANZ guidance on weathered AC cladding recommends professional assessment to determine whether encapsulation, overclad, or full removal is the right long-term answer. Leaving deteriorating AC cladding unaddressed can create bigger — and more expensive — problems down the track.

Building Consent Considerations

Simply sealing a crack does not typically require a building consent. However, if you are planning to reclad or remove the asbestos cement cladding as part of a larger project, you will likely need a consent under the Building Act 2004. Check with your local council, as requirements vary. The MBIE Building Performance website has useful guidance on consent requirements and Schedule 1 exemptions.

When to Call a Professional

Call a licensed asbestos removalist if:

• The cladding is crumbling, powdery, or friable in any way.
• The crack is large or the sheet is significantly damaged.
• You need to drill, cut, or remove any part of the cladding.
• You are not confident you can apply sealant without disturbing the surface.
• You want a professional assessment of the overall condition of your cladding.

A licensed asbestos assessor can also provide an asbestos management plan for your property — a worthwhile investment if you have significant AC cladding. You can find qualified asbestos removal specialists in your area on tradedirectory.co.nz.

Sources & Further Reading

• WorkSafe NZ – Asbestos guidance for homeowners
• MBIE Building Performance – Building consent information
• BRANZ – Building research and technical guidance
• Resene – Exterior paint and encapsulant products
• Bunnings – Sealants and caulking products
• Consumer NZ – Asbestos in the home