Finishing a concrete slab yourself is absolutely doable for a competent DIYer — provided you have the right tools and a clear plan before the concrete arrives. Concrete waits for no one, so being prepared is everything. Here's a practical rundown of the essential tools and how to use them.
Essential Tools for Finishing a Concrete Slab
Before the truck rolls up, have every tool clean, within arm's reach, and ready to go. Once the pour starts, you won't have time to hunt for anything.
Screeding Tools
- Screed board (or straight-edge): A straight length of timber (typically 100 × 50 mm H3 treated) or a purpose-made aluminium screed bar, long enough to span your form boards. You drag this across the top of the wet concrete to level it to the correct height.
- Bull float: A large, flat magnesium or aluminium float on a long handle. After screeding, you push and pull the bull float across the surface to close up voids, embed aggregate, and bring a thin layer of paste to the top. This is one of the most important tools for a good finish.
Hand Finishing Tools
- Magnesium hand float: Used after the bull float to further smooth and compact the surface once the bleed water has evaporated. Magnesium is preferred over wood for most NZ conditions as it doesn't drag.
- Steel trowel: For a smooth, hard finish — common on interior slabs and garage floors. You work the steel trowel in overlapping arcs once the concrete has stiffened enough to support your weight on knee boards. Timing is critical: too early and you'll tear the surface; too late and the concrete is unworkable.
- Edging tool: Rounds off the slab edges to prevent chipping and gives a neat, professional look. Run it along the inside of the form boards after screeding.
- Groover (jointing tool): Used to cut control joints into the slab surface. Control joints encourage any cracking to happen in a straight, planned line rather than randomly across the slab. As a guide, joints are typically spaced at 24–30 times the slab thickness (e.g., every 3–3.6 m for a 125 mm slab), though your specific design may vary — check with your engineer or concreter.
Support and Access Tools
- Knee boards: Flat boards (often 600 × 600 mm plywood) that spread your weight so you can kneel on the slab while hand-finishing without leaving marks.
- Rubber boots: Essential for walking in fresh concrete during the pour and screed stage.
- Concrete rake / come-along: A wide, flat rake used to spread and roughly level the concrete as it comes off the chute before screeding.
Measuring and Layout Tools
- Spirit level or laser level: To check your form boards are set to the correct fall (NZS 3604 and the NZ Building Code require floor slabs to drain correctly — typically a minimum 1:100 fall for outdoor slabs).
- Tape measure and string line: For setting out form boards accurately before the pour.
Optional but Useful Tools
| Tool | When You Need It |
|---|---|
| Power screed (vibrating) | Larger slabs (3 m+ wide) for faster, more consistent levelling |
| Angle grinder with diamond blade | Cutting control joints after the slab has cured |
| Concrete vibrator | Helps consolidate concrete around reinforcing steel |
| Broom | For a broom finish on driveways and paths (better grip) |
A broom finish is simply dragging a stiff-bristled broom across the surface just before it fully sets — it's a popular, slip-resistant choice for NZ driveways and outdoor areas.
Curing Equipment
Finishing doesn't end when the trowel goes down. Proper curing is critical for strength and durability, especially in NZ's variable climate.
- Plastic sheeting or curing compound: Keeps moisture in the slab so it cures slowly and evenly. Rapid drying in wind or sun causes surface cracking.
- Garden hose: For misting the surface if using wet curing methods.
For curing compounds and concrete finishing products, suppliers like Sika and Ardex offer NZ-stocked options worth checking out.
Where to Hire or Buy Tools in NZ
Most of these tools are available to buy or hire from Bunnings, Mitre 10, or PlaceMakers. For larger or specialist items like power screeds and concrete vibrators, tool hire is usually the most cost-effective option for a one-off job.
Do You Need a Building Consent?
This depends on the size and purpose of your slab. Many small concrete slabs (such as garden sheds or paths) fall under Schedule 1 exemptions of the Building Act, but slabs for habitable buildings, retaining structures, or anything attached to your home may require a building consent. Always confirm with your local council before you start — requirements vary by region. MBIE Building Performance has useful guidance on what work requires consent.
When to Call a Professional
Concrete finishing is physically demanding and very time-sensitive. If your slab is:
- Larger than about 20–25 m²
- Part of a structural floor, driveway, or foundation
- Requiring a specific engineered design (reinforcing, thicknesses, falls)
- In a complex shape with lots of edges and penetrations
…then it's well worth bringing in a qualified concreter. A poor finish is difficult and expensive to fix once the concrete has cured. You can find experienced local concreters on tradedirectory.co.nz who can either do the full job or at least advise on your specific situation.
For guidance on safe working practices around concrete (which is caustic and can cause skin burns), refer to WorkSafe NZ — always wear gloves, eye protection, and waterproof boots.
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