For outdoor brickwork in New Zealand, the most commonly used mortar mix is 1 part cement : 1 part lime : 6 parts sand (often written as 1:1:6), or a slightly stronger 1:0.5:4.5 mix for more exposed locations. The right ratio depends on your specific site conditions, the type of brick you're using, and how much weather exposure the wall will face.
Why the Mix Ratio Matters
Mortar does more than hold bricks together — it also allows a wall to flex slightly with temperature and moisture changes, and it needs to be slightly weaker than the bricks themselves. If mortar is too strong (too much cement), it can cause bricks to crack rather than letting the mortar joint absorb movement. Too weak, and the wall won't hold up to NZ's variable weather, including driving rain, frost in colder regions, and UV exposure.
BRANZ provides detailed guidance on mortar performance and durability for NZ conditions, and is a good reference if you want to dig deeper into the technical side.
Standard NZ Mortar Mix Ratios by Exposure
NZ bricklaying practice generally follows exposure-based classifications. Here's a guide to common mixes:
| Exposure Level | Typical Location | Recommended Mix (Cement:Lime:Sand) |
|---|---|---|
| Sheltered / Mild | Inland, protected walls | 1:1:6 |
| Moderate | Most suburban NZ locations | 1:0.5:4.5 |
| Severe / Coastal | Coastal, high-wind, frost zones | 1:0.25:3 or 1:0:3 |
- Sheltered (1:1:6): Good workability, flexible, suits most standard clay or concrete bricks in protected settings.
- Moderate (1:0.5:4.5): A good all-rounder for most NZ outdoor brickwork, balancing strength and flexibility.
- Severe (1:0.25:3 or stronger): Used in coastal areas exposed to salt spray, or in alpine/frost-prone regions like Central Otago or the central North Island.
Always check with your brick manufacturer for their specific recommendations — some bricks, particularly lower-density or recycled bricks, require a softer mortar to avoid damage.
What Type of Sand to Use
Use clean, well-graded bricklaying sand (also called plasterer's or brickies' sand). Avoid beach sand, which contains salt and can cause efflorescence and long-term damage. River sand or purpose-blended bricklaying sand from a builders' merchant is ideal. You can source materials from suppliers like Bunnings, Mitre 10, or PlaceMakers.
The Role of Lime
Hydrated lime (not agricultural lime) is added to mortar to improve workability, water retention, and flexibility. It makes the mortar easier to spread and helps it cure more slowly, which reduces cracking. For most outdoor brickwork, some lime content is recommended unless you're using a pre-blended masonry cement that already contains lime substitutes.
If you're using a pre-mixed mortar product, check the bag for the equivalent strength class — these are often labelled M2, M3, or M4, corresponding roughly to different exposure levels.
Mixing Tips for Best Results
- Measure by volume, not weight — use a bucket or shovel consistently.
- Mix dry ingredients thoroughly before adding water.
- Add water gradually; the mix should hold its shape when squeezed but not be crumbly or sloppy.
- Don't add more water once the mix has started to stiffen — discard and mix a fresh batch.
- In hot or windy weather, keep mixed mortar covered and work in smaller batches to prevent premature drying.
- In cold weather (below 5°C), avoid laying mortar as it may not cure properly and can be damaged by frost.
NZ Building Code Considerations
Outdoor brickwork that forms part of a building's structure or weathertight envelope may be subject to the NZ Building Code, particularly clauses B1 (Structure) and E2 (External Moisture). Structural masonry walls generally require a building consent, and the work must comply with NZS 4210: Masonry Construction. Freestanding garden walls under a certain height may be exempt under Schedule 1 — but always confirm with your local council before starting, as exemptions vary.
Pre-Mixed vs. Site-Mixed Mortar
Pre-mixed mortar (available in bags) is convenient for small jobs and takes the guesswork out of ratios. It's a good option for DIY repairs or small projects. For larger jobs, site-mixing from individual components is more economical and gives you more control over the mix design. Products from Sika and Ardex include specialist mortars for particular applications, such as below-ground or high-movement situations.
When to Call a Professional
While mixing mortar and laying bricks for small garden walls or repairs is within reach of a capable DIYer, there are situations where you should engage a qualified bricklayer or stonemason:
- Any structural brickwork forming part of a building (retaining walls over 1.5 m, house walls, chimneys).
- Work requiring a building consent — an Licensed Building Practitioner (LBP) may be required to carry out or supervise restricted building work.
- Coastal or high-exposure sites where getting the mix wrong could lead to rapid deterioration.
- Heritage or character brickwork where matching existing mortar is critical.
- If you're unsure about the structural implications of any wall.
You can find qualified, local bricklayers on tradedirectory.co.nz to get the job done right the first time.
Licensed Building Practitioner (LBP)
