Getting your site ready before the concreter arrives is one of the best things you can do to keep your project on time and on budget. A well-prepared site means the crew can get straight to work, reduces the risk of costly delays, and helps ensure your finished concrete meets the NZ Building Code requirements. Here's a practical guide to what you need to sort out beforehand.
Check Whether You Need a Building Consent
Before anything else, find out whether your concrete project requires a building consent. In New Zealand, some concrete work — such as a small garden path or a simple driveway — may be exempt under Schedule 1 of the Building Act, but larger slabs, foundations, or retaining walls often do require consent. Rules vary between councils, so always confirm with your local council before starting. Your concreter should also be able to advise you, and you can find general guidance at MBIE Building Performance.
Sort Out Vehicle and Equipment Access
Concrete trucks are large and heavy — typically 8–10 metres long and weighing up to 30 tonnes when loaded. Before the pour day:
- Measure your driveway and gate widths — most concrete trucks need at least 3 metres of clearance.
- Remove any vehicles, trailers, or obstacles from the access route.
- Check that the ground along the access route can handle the truck's weight without damaging underground services or soft ground.
- If direct truck access isn't possible, discuss with your concreter whether a concrete pump will be needed (this adds cost but is sometimes the only option).
- Let your neighbours know in advance, especially if the truck will need to park on or near the road.
Mark and Protect Underground Services
This is critical. Hitting a buried water pipe, gas line, or electrical cable during excavation or forming is dangerous and expensive. Before any digging:
- Contact Dial Before You Dig (0800 248 344) to get your underground services located and marked.
- Mark the locations clearly with spray paint or flags.
- Keep your concreter informed of where services run.
For electrical safety information, refer to WorkSafe NZ.
Prepare the Ground
The ground beneath your concrete is just as important as the concrete itself. Poor sub-base preparation is one of the most common causes of cracking and settlement.
Excavation and Levels
- Excavate to the depth your concreter specifies — for a typical residential slab this is often 100–150 mm below finished surface level, but your concreter will confirm based on the design.
- Remove all topsoil, organic material, tree roots, and soft spots. Organic material will decompose and cause settlement.
- Ensure the base is firm and even. If you have soft or unstable ground, discuss with your concreter whether additional fill or compaction is needed.
Compacted Hardfill
- A layer of compacted AP20 or AP40 hardfill (crushed aggregate) is typically placed over the prepared subgrade. Your concreter will usually specify the depth.
- Hardfill must be properly compacted — a plate compactor is the right tool for this job. Loose fill will cause problems later.
- In some situations, a layer of polythene (visqueen) is placed over the hardfill as a vapour barrier, particularly for interior slabs.
Set Up Formwork
Formwork (also called shuttering) is the timber or steel framework that holds the wet concrete in shape until it sets. Your concreter will usually install the formwork themselves, but you can help by:
- Having the area clear and accessible.
- Ensuring the ground is already at the right level so formwork can be set accurately.
- Discussing the finished levels and any falls (slopes for drainage) with your concreter beforehand — for outdoor areas, a fall of at least 1:100 away from buildings is generally recommended to manage surface water in line with NZ Building Code clause E1 (Surface Water).
Consider Reinforcing Steel
Many concrete slabs require reinforcing mesh or rebar to add tensile strength and control cracking. Your concreter or engineer will specify what's needed. If you're supplying the mesh yourself (sometimes done to save cost), make sure it's on site and dry before the crew arrives. Mesh should be supported on bar chairs so it sits at the correct height within the slab — not lying flat on the ground.
Plan for Curing and Finishing
Think ahead about what happens after the pour:
- Keep the area clear of foot traffic and vehicles for at least 24–48 hours after the pour, and longer for full strength (concrete typically reaches design strength at 28 days).
- Arrange for a curing compound or wet hessian to be available if your concreter requires it — curing is especially important in hot, dry, or windy NZ conditions to prevent surface cracking.
- Discuss the surface finish you want (broom finish, exposed aggregate, smooth trowel) before the day so the right tools and techniques are ready.
Communicate Clearly With Your Concreter
Before the pour day, have a clear conversation with your concreter about:
| Topic | What to Confirm |
|---|---|
| Concrete mix | Strength (MPa), aggregate size, any additives |
| Volume | Double-check the cubic metre order |
| Timing | Truck arrival time, how long the pour will take |
| Weather | Postpone if heavy rain or extreme heat is forecast |
| Access | Confirm truck route and any pump requirements |
For guidance on concrete specifications and standards, BRANZ is a useful NZ resource.
When to Call a Professional
While homeowners can do much of the preparation work described above, the actual concrete pour and finishing should be handled by an experienced concreter. Concrete has a limited working time and mistakes are very difficult to fix once it sets. If your project involves structural foundations, retaining walls, or any work requiring a building consent, you may also need input from a Licensed Building Practitioner (LBP) — find out more at Licensed Building Practitioners. Any electrical or plumbing work associated with your project must be carried out by licensed tradespeople under NZ law.
You can find qualified, local concreters on tradedirectory.co.nz.
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