Is It Safe to Use a Wire Brush on Weathered Asbestos Cement Cladding?

No — using a wire brush on weathered asbestos cement cladding is not safe and is strongly discouraged under New Zealand health and safety regulations. Weathered asbestos cement is friable (easily crumbled), meaning mechanical abrasion like wire brushing can release microscopic asbestos fibres into the air, where they can be inhaled and cause serious, irreversible lung diseases including mesothelioma and asbestosis. This is a situation where the risks are too high to take shortcuts.

Why Weathered Asbestos Cement Is So Dangerous

Asbestos cement (often called fibrolite or AC sheet in New Zealand) was widely used in cladding, roofing, and eaves lining on homes built before the mid-1980s. When the material is in good condition and left undisturbed, the risk is relatively low because the fibres are locked into the cement matrix. However, weathered or degraded asbestos cement is a different matter entirely:

• The cement binder breaks down over time due to UV exposure, moisture, and freeze-thaw cycles
• The surface becomes chalky, pitted, or flaking — signs the fibres are no longer well-bound
• Any mechanical disturbance — including wire brushing, sanding, grinding, or pressure washing — can release fibres into the air
• Fibres are invisible to the naked eye and can remain airborne for hours

The more weathered the sheet, the greater the risk. If you can scratch the surface with a fingernail and it crumbles or powders, treat it as friable asbestos and do not touch it without professional advice.

What NZ Law Says

In New Zealand, work involving asbestos is regulated under the Health and Safety at Work (Asbestos) Regulations 2016, administered by WorkSafe NZ. Key points for homeowners:

• Class A asbestos removal (friable asbestos or more than 10 m² of non-friable material) must be carried out by a licensed asbestos removalist
• Class B asbestos removal (non-friable material up to 10 m²) can be done by a competent person following strict controls, but this still requires proper PPE, containment, and disposal procedures
• Wire brushing weathered (friable) asbestos cement almost certainly falls into Class A territory — meaning it is restricted work that a homeowner should not attempt
• Illegal or improper asbestos work can result in significant fines under the Health and Safety at Work Act 2015

If you are unsure whether your cladding contains asbestos, do not disturb it. Arrange for a sample to be collected and tested by an accredited laboratory — this should also be done by a trained professional to avoid releasing fibres during sampling.

What You Should Do Instead

If your weathered asbestos cement cladding needs attention, here are the safer, compliant options:

Leave it alone if it's stable

If the cladding is weathered but not flaking or crumbling, and you don't need to disturb it, the safest option is often to leave it in place and monitor it regularly.

Encapsulation (sealing)

For cladding that is mildly weathered but still reasonably intact, encapsulation — applying a penetrating sealer or paint — can stabilise the surface and reduce fibre release. This must be done carefully:

• Do not wire brush, sand, or abrade the surface beforehand
• Gently remove loose dirt with a damp cloth or very low-pressure rinse (no pressure washing)
• Use a suitable encapsulant or exterior paint recommended for asbestos cement — paint suppliers such as Resene or Dulux can advise on appropriate products
• Even encapsulation on friable material should be assessed by a professional first

Professional removal and replacement

If the cladding is badly degraded, cracked, or needs to be removed for renovation work, engage a licensed asbestos removalist. They will:

• Conduct or arrange an asbestos survey
• Set up proper containment and use appropriate PPE
• Dispose of the material at an approved facility in accordance with NZ regulations
• Provide clearance documentation

You can find licensed asbestos removal specialists in your area on tradedirectory.co.nz.

Safe Practices If You Must Be Near the Cladding

If you need to work near (not on) asbestos cement cladding — for example, painting adjacent surfaces — take these precautions:

• Do not drill, cut, sand, or scrub the asbestos cement surface
• Wear a properly fitted P2 respirator (not a dust mask) if you are working in the vicinity
• Keep the area well ventilated
• Dampen the surface lightly with water if you accidentally disturb it, to suppress dust
• Bag and dispose of any debris carefully — check with your local council for approved disposal sites

For broader guidance on managing asbestos in the home, BRANZ provides research-based technical information relevant to New Zealand conditions.

Building Consent Considerations

Replacing asbestos cement cladding with new cladding may require a building consent, depending on the scope of work and your local council's interpretation of Schedule 1 exemptions under the Building Act 2004. Always check with your local council before starting any cladding replacement work. The MBIE Building Performance website has useful guidance on when consent is required.

When to Call a Professional

Call a licensed asbestos removalist if:

• Your cladding is visibly weathered, chalky, crumbling, or flaking
• You need to remove, repair, or drill into asbestos cement
• You are planning a renovation that will disturb the cladding
• You are unsure of the condition or extent of asbestos-containing materials on your property

Do not attempt to wire brush, sand, grind, or pressure wash weathered asbestos cement under any circumstances. The health consequences — which may not appear for decades — are simply not worth the risk.

Sources & Further Reading

• WorkSafe NZ – Asbestos
• BRANZ – Building Research
• MBIE Building Performance – Building Consent
• Resene – Exterior Paints & Sealers
• Standards NZ