Getting your property ready before a concreting job starts is one of the best things you can do to keep the project on time and on budget. A well-prepared site means your concreters can hit the ground running, the finished slab will perform better, and you'll avoid costly delays or rework. Here's a practical guide for NZ homeowners.
Check Whether You Need a Building Consent
Before any work begins, find out whether your project requires a building consent. In New Zealand, many concrete slabs — such as driveways, paths and small garden pads — fall under Schedule 1 exemptions of the Building Act 2004, meaning consent may not be required. However, this depends on the size, use and location of the slab. Concrete floors for habitable rooms, garages, or structures attached to your home almost always require consent.
Always confirm with your local council before starting. MBIE Building Performance has clear guidance on what work is exempt and what isn't. Getting this wrong can cause problems when you sell your home.
Clear and Mark the Site
Your concreters need a clean, accessible work area. Before they arrive:
- Remove all vegetation, including grass, weeds, tree roots and garden edging from the area to be concreted.
- Relocate outdoor furniture, pots, garden ornaments and any other items that could get in the way.
- Mark out underground services — water pipes, irrigation lines, electrical conduits and drainage. Call Before U Dig (0800 248 344) to locate any buried services. Hitting a pipe or cable during excavation is dangerous and expensive.
- Protect garden beds and lawn edges near the work zone with temporary boarding or plastic sheeting, as concrete splatter and foot traffic can cause damage.
Sort Out Access for the Concrete Truck
Concrete truck access is critical and often overlooked. A loaded ready-mix truck can weigh over 30 tonnes, so you need to think carefully about:
- Driveway and gate width — most trucks need at least 3 metres of clearance.
- Overhead obstacles — check for low-hanging branches, power lines or carport beams.
- Ground conditions — soft or wet ground can cause a heavy truck to sink or damage your lawn and existing paths.
- Parking and turning space — the truck may need room to manoeuvre or reverse.
If direct truck access isn't possible, your concreters may need to use a concrete pump, which adds cost. Discuss this with your contractor early.
Prepare the Sub-base
A solid, well-compacted sub-base is the foundation of any good concrete slab. Poor sub-base preparation is one of the leading causes of cracking and slab failure in NZ.
- Excavate to the correct depth — your concreters will advise, but typically 100–150 mm of excavation is needed for a standard residential slab, allowing for compacted fill and the concrete itself.
- Compact the sub-grade — loose or soft soil must be compacted with a plate compactor. In some cases, poor soil may need to be removed and replaced with compacted AP40 (aggregate) or similar.
- Install drainage if needed — if water pools in the area, address drainage before concreting. Concrete over a wet or poorly drained sub-base will underperform.
- Check levels and falls — concrete around homes should fall away from the building at a minimum gradient to prevent water pooling. Your concreters will set this up, but it helps to discuss it beforehand.
BRANZ provides technical guidance on ground preparation and slab construction that is well worth reviewing.
Organise Formwork and Reinforcing
Your concreters will typically handle formwork (the timber or steel frames that hold the wet concrete in shape) and reinforcing (steel mesh or rebar that strengthens the slab). However, as the homeowner you should:
- Confirm with your contractor what reinforcing is specified — for driveways, 665 mesh or 768 mesh is common; structural slabs may require engineer-specified rebar.
- Ensure the formwork area is pegged out and agreed upon before the pour day.
- If you're supplying any materials yourself, have them on site well in advance.
Notify Your Neighbours
Concreting can be noisy and disruptive. A concrete pour often involves early starts, heavy vehicles and workers moving around your property. Give your neighbours a heads-up, especially if the truck will be parked on or near the street. This is good practice and helps maintain good relationships.
Plan for the Weather
NZ weather can be unpredictable. Concrete should not be poured in heavy rain, extreme heat or frost. Work with your concreters to choose a suitable day and have a contingency plan. In summer, early morning pours help avoid rapid drying in the heat. In winter, especially in the South Island and central North Island, frost protection may be needed after the pour.
When to Call a Professional
Concreting is physically demanding, technically precise work. While a homeowner can do some preparation tasks — like clearing vegetation or moving furniture — the actual concrete pour, formwork, reinforcing and finishing should be handled by an experienced concreters. Poorly finished concrete is very difficult to fix once it has set.
If your project involves any structural elements, retaining walls (check with your council for the relevant height thresholds that trigger consent or LBP requirements), or a slab for a habitable room, you may also need input from a Licensed Building Practitioner (LBP). Check the LBP register to find qualified professionals in your area.
You can find experienced, local concreting contractors on tradedirectory.co.nz to get quotes and advice specific to your project.
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