Finishing concrete edges with a float is one of the most satisfying parts of a concrete job — when done right, it produces a smooth, rounded edge that resists chipping and looks professional. The key is using the correct tool at the right time, with a steady, confident hand. Here's everything a NZ homeowner needs to know.
Understanding the Tools: Edger vs Float
Before diving into technique, it helps to know your tools:
- Bull float – A large, long-handled float used across the full slab surface to level and compact the concrete just after screeding.
- Hand float (or wooden/magnesium float) – Used to smooth the surface by hand once the bleed water has evaporated.
- Steel trowel – Used after floating for a harder, smoother finish (not always needed for outdoor slabs).
- Concrete edging tool (edger) – A specialised float with a curved lip, designed specifically to round and compact the edge of a slab. This is the primary tool for finishing edges.
For edge work, you'll mainly use the edging tool and a hand float together. You can find both at Bunnings or Mitre 10.
Timing Is Everything
The single biggest mistake DIYers make is working the concrete too early or too late. You need to wait until the bleed water (the sheen of water that rises to the surface) has fully evaporated before you begin floating and edging.
- If you work too early, you'll weaken the surface by working water back into it.
- If you wait too long, the concrete will be too stiff to work properly.
In NZ conditions, this waiting period can vary significantly — hot, dry nor'wester days in Canterbury or Central Otago will speed things up considerably, while cool, humid days in Auckland or Wellington will slow things down. Always watch the surface, not the clock.
Step-by-Step: Finishing Concrete Edges with a Float
1. Initial Screeding and Bull Floating
After the concrete is poured and screeded level, run a bull float across the entire surface. This embeds the aggregate and brings a thin layer of cement paste to the top. Work the bull float in overlapping passes, keeping the leading edge slightly raised.
2. Wait for Bleed Water to Evaporate
Be patient. Once the surface has lost its sheen and the concrete can support your weight on a kneeling board without leaving deep impressions, you're ready to edge.
3. Run the Edging Tool Along the Form
- Hold the edging tool flat against the surface with the curved lip running along the inside of the formwork (timber frame).
- Apply gentle downward pressure and move the tool back and forth in smooth, overlapping strokes — roughly 300–400 mm at a time.
- The curved lip will compact and round the edge, pushing aggregate away from the corner and creating a neat radius.
- Keep the tool flat — tilting it too much will dig in and leave marks.
- Wipe any concrete that builds up on the tool with a damp rag.
4. Follow Up with a Hand Float
After edging, use a magnesium or wooden hand float to smooth any tool marks left just inside the edge. Hold the float nearly flat and use a circular or arcing motion, then finish with long, straight strokes parallel to the edge.
5. Re-edge After Floating
Floating can slightly disturb the edge you've just created. Run the edging tool along the perimeter one more time for a crisp, clean finish.
6. Optional: Steel Trowel Finish
For interior slabs or areas requiring a harder surface, follow up with a steel trowel after the second edging pass. For outdoor paths, driveways, and patios, a floated or broom finish is generally preferred for slip resistance — important under the NZ Building Code.
Tips for a Professional Result
| Tip | Why It Matters |
|---|---|
| Keep tools clean and damp | Prevents concrete sticking and dragging |
| Work in the shade if possible | Slows drying, gives more working time |
| Use a kneeling board | Distributes your weight, avoids surface damage |
| Edge before and after floating | Ensures a crisp, well-compacted edge |
| Avoid overworking the surface | Brings too much water/cement to the top, weakening it |
Curing After Finishing
Once you've finished the edges and surface, curing is critical. Cover the slab with plastic sheeting or apply a curing compound to retain moisture for at least 3–7 days. This is especially important in NZ's variable climate. Proper curing significantly improves the final strength and durability of your concrete. BRANZ has useful guidance on concrete construction best practice.
Do You Need a Building Consent?
For many small concrete projects (garden paths, patios under a certain size), a building consent may not be required under Schedule 1 of the Building Act. However, rules vary by project type and local council. Always check with your local council before starting to confirm whether your project is exempt. The MBIE Building Performance website is a good starting point.
When to Call a Professional
Concrete work looks straightforward but can go wrong quickly, especially on larger pours. Consider hiring a qualified concreter if:
- You're pouring a driveway, garage floor, or structural slab.
- The area is large (anything over about 10–15 m² can be challenging for a first-timer).
- You need a specific finish standard for compliance or aesthetics.
- You're unsure about mix ratios, reinforcing, or sub-base preparation.
A professional concreter will have the right equipment, experience with NZ conditions, and knowledge of local council requirements. You can find qualified local concreters on tradedirectory.co.nz.
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