Tree roots lifting or cracking a concrete path are a common headache for NZ homeowners, especially where large natives or exotic trees grow close to paved areas. The good news is that with the right tools and approach, many repairs are well within DIY reach — though more extensive work is best left to a qualified concreter.
Assess the Damage First
Before reaching for a sledgehammer, take stock of what you're dealing with:
- Minor cracking (hairline to around 5 mm wide, no lifting): may be patchable in place.
- Moderate damage (cracked slabs, slight lifting): individual sections can often be removed and relaid.
- Severe heaving or widespread cracking: the path may need full removal and replacement.
Also check whether the path is close to your house foundation, retaining walls, or any underground services (water, drainage, gas, power). If roots have reached these areas, the scope of work grows considerably. Contact your local council or a licensed tradesperson before proceeding.
Tools and Materials You'll Need
- Safety glasses, heavy-duty gloves, and steel-capped boots
- Angle grinder with a diamond blade (for cutting control joints)
- Electric demolition hammer or cold chisel and club hammer
- Pry bar
- Root saw, loppers, or reciprocating saw
- Wheelbarrow and skip bin (for concrete rubble)
- Compactor plate or hand tamper
- Concrete mix (bagged or ready-mix, depending on area size)
- Formwork timber (if relaying sections)
- Reinforcing mesh (for slabs thicker than 75 mm)
Safety note: Concrete rubble is heavy and sharp. Always wear PPE. If you're cutting concrete, use a wet-cutting method or wear a P2 dust mask — concrete dust contains silica and poses a serious health risk. See WorkSafe NZ for guidance on working safely with silica dust.
Step 1 — Cut Around the Damaged Section
Using an angle grinder fitted with a diamond blade, score along existing control joints or cut new straight lines around the damaged slab(s). Cutting clean edges makes removal easier and gives you a neat boundary for the repair. Keep cuts straight and square.
Step 2 — Break Out the Concrete
Use a demolition hammer (hire one from Bunnings or Mitre 10 if you don't own one) to break the slab into manageable pieces. Work from the centre outward. Use a pry bar to lever pieces free. Stack rubble in a wheelbarrow and dispose of it at a transfer station — most councils accept clean concrete for recycling.
Step 3 — Deal with the Tree Roots
This is the critical step. Simply removing the concrete and relaying it without addressing the roots means the problem will return.
- Cut offending roots using a root saw, sharp loppers, or a reciprocating saw. Remove only what is necessary — cutting major roots can destabilise or kill the tree.
- Consider the tree's value: If the tree is large, mature, or protected (some councils have rules around protected trees), consult an arborist before cutting any roots. Check with your local council about any tree protection rules in your area.
- Root barriers: After cutting, install a physical root barrier (a rigid plastic sheet, typically 300–600 mm deep) along the path edge to redirect future growth downward and away from the concrete.
- Treat cut roots: Some arborists recommend treating cut root ends to discourage regrowth — seek advice from a qualified arborist for your specific tree species.
Step 4 — Prepare the Sub-base
A solid sub-base is what separates a lasting repair from one that fails again in a few years.
- Excavate to a depth of at least 150 mm below finished path level (100 mm of compacted sub-base + 75–100 mm of concrete).
- Fill with AP20 compacted gravel (available from landscape suppliers and PlaceMakers) in layers, compacting each layer thoroughly.
- Check the surface is level and well-drained — poor drainage is a common cause of ongoing path problems in NZ's wetter regions.
Step 5 — Set Formwork and Pour Concrete
- Set timber formwork to match the existing path level and width.
- For paths, a 75–100 mm slab is typical. Add reinforcing mesh (SL72 or similar) for slabs at the thicker end or in areas with heavy foot traffic.
- Mix and pour concrete, screed level with the surrounding path, and finish with a broom finish for slip resistance — important in NZ's wet winters.
- Allow at least 7 days before light foot traffic, and 28 days for full cure.
- Cut or tool control joints every 1.2–1.5 m to manage future cracking.
Does This Work Need a Building Consent?
Replacing a damaged residential path section is generally exempt from building consent under Schedule 1 of the Building Act 2004, but this depends on the scope and location. Always confirm with your local council before starting work, particularly if the path is near a boundary, retaining structure, or drainage system. See MBIE Building Performance for general guidance.
When to Call a Professional
Consider hiring a qualified concreter (find one on tradedirectory.co.nz) if:
- The damaged area is large (more than a few square metres)
- Roots have reached underground services — gas, water, or electrical lines must only be worked on by licensed tradespeople (PGDB for plumbing/drainage, EWRB for electrical)
- The path is structural (e.g., a driveway or load-bearing surface)
- You're unsure about sub-base preparation or drainage
- The tree is large, protected, or its root system is extensive
A professional concreter will also have access to ready-mix concrete and compaction equipment that produces a more consistent, durable result for larger jobs.
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