Laying your own concrete path or garden slab is a satisfying weekend project that many New Zealand homeowners tackle successfully each year. With the right preparation, tools, and a bit of patience, a basic path or non-structural slab is well within DIY reach. That said, larger or structural pours — like a garage floor, driveway, or anything near the house foundation — are a different story, and it pays to know where the line is.
What Can a Homeowner Legally Do?
In New Zealand, laying a simple garden path or a small decorative slab generally does not require a building consent, provided it is not structural and does not affect drainage or the building envelope. However, if your slab is attached to or supports a structure (like a carport or deck), or if it involves changes to stormwater drainage, you may need consent under the NZ Building Code. When in doubt, check with your local council before you start.
Planning and Design
Before you mix a single bag, spend time on planning:
- Purpose: Is it a garden path, a patio, a shed base, or a driveway? Each has different thickness and strength requirements.
- Thickness: As a general guide, a pedestrian path needs around 75–100 mm of concrete; a shed base or light vehicle area typically needs 100 mm or more.
- Sub-base: A well-compacted sub-base of crushed gravel (AP20 or similar) is essential for a long-lasting result. Skipping this step is the most common DIY mistake.
- Drainage: Concrete must be laid with a slight fall (typically around 1:100) so water runs away from buildings and doesn't pool. Check your local council rules around stormwater.
- Reinforcing: For most small paths, reinforcing mesh or fibres may not be strictly necessary, but for slabs over about 2 m wide or in areas with soft ground, adding reinforcing mesh (such as SE62 mesh) significantly reduces cracking.
Tools and Materials You'll Need
| Item | Notes |
|---|---|
| Timber formwork (pegs & boards) | Sets the shape and level of your slab |
| Spade & wheelbarrow | For excavation and moving concrete |
| Plate compactor (hire) | Compacts the sub-base properly |
| Screed board / straight edge | Levels the wet concrete |
| Bull float or darby | Smooths the surface |
| Steel trowel | For a smooth finish |
| Edging tool | Creates neat, rounded edges |
| Concrete mix or ready-mix | See below |
| Plastic sheeting | For curing |
You can hire most of these tools from your local Mitre 10 or Bunnings store, or from a local hire centre.
Choosing Your Concrete Mix
For small jobs, bagged concrete mix (just add water) is convenient and available at most hardware stores. For anything over about 1–2 cubic metres, ordering ready-mix concrete from a local supplier is far more practical and usually more consistent in quality.
- Bagged mix: Good for small patches, post holes, and short paths. Follow the manufacturer's water ratio carefully — too much water weakens the mix significantly.
- Ready-mix: Specify the strength (commonly 17.5 MPa or 20 MPa for residential paths and slabs). Tell the supplier what you're using it for and they'll advise the right mix.
- Fibre-reinforced mix: Some suppliers offer polypropylene fibre added to the mix, which helps control shrinkage cracking.
BRANZ has useful technical guidance on concrete performance for residential applications.
Step-by-Step: Laying a Basic Concrete Path
- Mark out and excavate to the required depth (sub-base + concrete thickness). Remove all topsoil and organic material.
- Compact the sub-base using a plate compactor. Add and compact crushed gravel in layers.
- Set your formwork — timber boards held in place with pegs, set to the correct level and fall.
- Place any reinforcing mesh, supported on small plastic chairs so it sits mid-depth in the slab.
- Pour and spread the concrete, working it into corners and around mesh with a rake or shovel.
- Screed the surface by dragging a straight board across the formwork to level the concrete.
- Float and finish the surface. For a non-slip texture outdoors, drag a stiff broom across the surface (a broom finish).
- Edge the slab with an edging tool while the concrete is still workable.
- Cure the concrete by covering with plastic sheeting for at least three to seven days. Curing is critical — don't let it dry out too fast, especially in hot or windy NZ conditions.
- Remove formwork after a few days and seal expansion joints if needed.
Common Mistakes to Avoid
- Adding too much water to the mix (weakens the concrete and causes cracking)
- Poor or uncompacted sub-base
- Working too slowly — concrete has a limited working time, especially in summer
- Not allowing for expansion joints on longer runs
- Finishing the surface too early while bleed water is still present
When to Call a Professional
Some concrete work is best left to an experienced concreter:
- Driveways — need proper thickness, reinforcing, and often a crossfall design
- Structural slabs — garage floors, house slabs, and anything supporting a building may require engineering input and building consent
- Large pours — coordinating a ready-mix truck and a crew to screed and finish quickly is not easy solo
- Decorative finishes — exposed aggregate, polished concrete, and stamped concrete require specialist skills and equipment
- Sloped or difficult sites — retaining, drainage, and access issues add complexity
If your project falls into any of these categories, it's worth getting a qualified concreter involved. You can find licensed local concreters in your area at tradedirectory.co.nz.