Mixing concrete for a fence post footing by hand is a straightforward DIY job most NZ homeowners can tackle with the right technique and a bit of muscle. The key is getting your cement-to-aggregate ratio correct, adding water gradually, and achieving a consistency that's stiff enough to support the post but workable enough to fill the hole properly. Here's everything you need to know.
What You'll Need
Before you start, gather your materials and tools:
- Portland cement (standard grey cement, available in 20 kg bags)
- Coarse sand (also called sharp or concreting sand)
- 20 mm aggregate (crushed stone or gravel)
- Clean water
- A large mixing tub, wheelbarrow, or flat mixing board
- A square-mouth shovel or spade
- A hoe or mixing paddle
- Measuring buckets (a standard 10–12 litre bucket works well)
- Safety gloves, safety glasses, and waterproof boots
Alternatively, you can use bagged premix concrete (cement, sand, and aggregate already combined), which simplifies the process — just add water. Premix bags are widely available at Bunnings and Mitre 10, and are ideal for small jobs like fence post footings.
The Right Concrete Mix Ratio
For fence post footings, a standard 1:2:3 mix is recommended:
| Component | Parts by Volume | Example (buckets) |
|---|---|---|
| Cement | 1 | 1 bucket |
| Sand | 2 | 2 buckets |
| Aggregate (20 mm) | 3 | 3 buckets |
This produces a general-purpose concrete suitable for most residential fence post footings. If you're using bagged premix, follow the manufacturer's instructions on the bag — they'll specify the water-to-bag ratio.
How Much Water to Add
Water is the most critical variable. Too much water weakens the concrete significantly; too little makes it unworkable and hard to compact around the post.
- As a rough guide, you'll need approximately 0.5 litres of water per kilogram of cement, but always add water gradually — a little at a time.
- The finished mix should hold its shape when squeezed in your hand but not be crumbly or sloppy. Think of a consistency similar to thick porridge or peanut butter.
- On hot, dry NZ summer days, your mix may need slightly more water due to faster evaporation — but resist the temptation to over-water.
Step-by-Step Mixing Process
1. Measure and combine dry ingredients
Add your measured sand and aggregate to the mixing tub or wheelbarrow first, then add the cement on top. Mix the dry ingredients together thoroughly with your shovel or hoe until the colour is uniform — no streaks of grey cement or pale sand.
2. Form a well and add water
Create a hollow in the centre of your dry mix (like a volcano). Pour in roughly half your estimated water into the well. Begin folding the dry mix into the water from the edges inward.
3. Mix thoroughly
Keep turning and folding the mix, adding small amounts of water as needed. Work from the bottom of the tub to ensure no dry material is left underneath. Aim for a consistent, lump-free mix with no dry pockets.
4. Check consistency
Grab a handful and squeeze — it should hold together and show your finger marks without water bleeding out. If it crumbles, add a splash more water. If water pools on the surface, you've added too much (add a little more dry mix to correct it).
5. Use it promptly
Hand-mixed concrete begins to set within 30–45 minutes, so have your post positioned and your hole ready before you start mixing. Don't mix more than you can use in one go.
Placing the Concrete
- Set your fence post in the hole at the correct depth (as a general guide, bury at least one-third of the post's total length, or follow your fence manufacturer's specifications).
- Brace the post plumb (perfectly vertical) using temporary stakes and string lines before pouring.
- Pour the concrete in layers, rodding or tamping with a stick after each layer to remove air pockets.
- Mound the concrete slightly above ground level and slope it away from the post to shed rainwater — this helps prevent rot and moisture ingress at the base.
- Allow at least 24–48 hours before attaching rails or applying load to the post.
Safety Notes
Wet cement is caustic and can cause serious skin burns with prolonged contact. Always wear waterproof gloves, safety glasses, and protective footwear. If cement contacts your skin, wash it off immediately with clean water. For more guidance, refer to WorkSafe NZ.
Do You Need a Building Consent?
Most residential fences don't require a building consent under Schedule 1 of the Building Act, but there are exceptions — for example, fences over 2.5 metres high, retaining walls, or fences near boundaries in certain zones. Always check with your local council before starting, as rules vary by region. The MBIE Building Performance website has useful guidance on consent exemptions.
When to Call a Professional
Hand-mixing is fine for a handful of fence posts, but for larger fencing projects, retaining structures, or if you're unsure about ground conditions (e.g., soft, wet, or sloping ground), it's worth calling in a qualified concreter. A professional can assess the site, recommend the right mix strength, and ensure the footings comply with NZS 3604 or other relevant standards. You can find experienced local concreters on tradedirectory.co.nz.
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