Removing old asbestos-containing mastic (adhesive) from a concrete floor yourself is strongly discouraged and, in most situations, illegal in New Zealand. Floor mastic used before the mid-1980s frequently contained chrysotile (white) asbestos, and disturbing it can release dangerous fibres into the air. Here is what you need to know before you touch a thing.
What Is Asbestos Mastic and Why Is It Dangerous?
Mastic is the black or dark-brown bitumen-based adhesive used to bond vinyl tiles, sheet vinyl, and cork tiles to concrete subfloors. In homes and commercial buildings constructed or renovated before 1990, this adhesive very commonly contained asbestos fibres. When the mastic is scraped, ground, or heated, it can become friable — meaning it crumbles and releases microscopic asbestos fibres that, when inhaled, can cause mesothelioma, asbestosis, and lung cancer decades later.
Even mastic that looks solid and intact can release fibres if disturbed aggressively. The risk is real, and WorkSafe NZ treats asbestos exposure as one of the leading causes of work-related deaths in New Zealand.
NZ Law: What Are You Actually Allowed to Do?
Under the Health and Safety at Work (Asbestos) Regulations 2016, asbestos removal work is divided into two classes:
| Class | Type of Work | Who Can Do It |
|---|---|---|
| Class A | Friable asbestos or any bonded asbestos over 10 m² | Licensed Class A removalist only |
| Class B | Non-friable (bonded) asbestos up to 10 m² | Licensed Class B or Class A removalist |
| Homeowner exemption | Non-friable, on your own home, under 10 m² | Homeowner may do this, with strict controls |
The critical point: if the total area of asbestos-containing mastic exceeds 10 m², you must hire a licensed asbestos removalist — full stop. Even under 10 m², the homeowner exemption only applies to your own home (not a rental), and you must still follow strict WorkSafe guidelines on PPE, containment, and disposal.
Mastic is generally considered non-friable (bonded) asbestos when intact, but scraping or grinding it can make it friable — which immediately pushes the work into Class A territory, requiring a licensed professional regardless of area.
MBIE Building Performance also notes that any associated building work may require a building consent — check with your local council before starting.
Getting the Mastic Tested First
Before assuming the mastic contains asbestos, have it tested. A sample should be collected by a trained asbestos assessor and sent to an accredited laboratory. Do not attempt to collect samples yourself without proper training and PPE — even sampling can disturb fibres.
An asbestos assessor can provide a written asbestos management plan or clearance report, which is best practice before any floor renovation in a pre-1990 building.
The Safer Alternative: Encapsulation or Overlay
In many situations, the safest and most practical option is not to remove the mastic at all. If the mastic is in good condition (not flaking or crumbling), you may be able to:
- Encapsulate it with an approved sealant
- Overlay the floor with new flooring directly on top (check with your flooring installer and confirm the floor height works for your situation)
- Apply a self-levelling compound over the mastic before laying new flooring — products from suppliers such as Ardex or Mapei may be suitable, but always confirm compatibility with an asbestos assessor first
This approach avoids disturbing the asbestos entirely and is often recommended by BRANZ, New Zealand's building research authority.
If You Qualify for the Homeowner Exemption (Under 10 m²)
If the area is genuinely under 10 m², the mastic is confirmed non-friable, and it is your own home, you may proceed — but only with strict precautions:
- PPE: Wear a properly fitted P2 (or P3) half-face respirator — not a dust mask. Disposable coveralls, gloves, and eye protection are essential.
- Wet methods only: Keep the mastic wet throughout to suppress dust. Never dry-scrape, sand, or use power tools.
- Containment: Seal off the work area. Lay plastic sheeting on the floor and over doorways.
- Disposal: Double-bag all waste in heavy-duty plastic bags, label them as asbestos waste, and dispose of them at an approved facility. Contact your local council for approved drop-off sites.
- No children or other people in or near the work area.
Review the full WorkSafe guidance at WorkSafe NZ before starting.
When to Call a Professional
You should always hire a licensed asbestos removalist if:
- The total mastic area is 10 m² or more
- You need to scrape, grind, or use heat to remove it (making it friable)
- The mastic is flaking, crumbling, or already disturbed
- The property is a rental (the homeowner exemption does not apply)
- You have any doubt about the extent or condition of the asbestos
- You want a clearance certificate for peace of mind or for sale/renovation purposes
A licensed Class A or Class B asbestos removalist has the training, equipment, and legal authority to do this work safely. You can find qualified local asbestos removal specialists on tradedirectory.co.nz. Always ask to see their WorkSafe licence before work begins.
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