Repointing an older New Zealand brick home with the correct lime mortar is one of the most important things you can do to protect the building's long-term health. Using the wrong mortar — particularly modern cement-rich mixes — can cause serious damage to heritage brickwork over time. The good news is that with the right materials and a careful approach, mixing a suitable lime mortar is a manageable DIY task for small areas.
Why Lime Mortar Matters for Older Brickwork
Most NZ homes built before the 1950s used lime-based mortars, which are softer and more flexible than modern Portland cement mortars. This flexibility is intentional: in a traditional masonry wall, the mortar is designed to be the sacrificial element, absorbing movement and moisture rather than the bricks themselves.
If you repoint with a hard cement mortar, it can't flex with the wall. Moisture and movement stress then transfer directly into the bricks, causing spalling, cracking, and long-term structural damage — especially in New Zealand's variable climate, where freeze-thaw cycles in colder regions and coastal salt exposure are real concerns.
BRANZ has well-established guidance on the importance of matching mortar strength to the original masonry, and it's worth reviewing before you start.
Understanding Lime Mortar Ingredients
A traditional lime mortar has three main components:
- Lime putty or hydraulic lime — the binder. For most heritage repointing, non-hydraulic lime putty or natural hydraulic lime (NHL) is used. NHL 2 or NHL 3.5 are common choices for NZ conditions — NHL 3.5 suits slightly wetter or more exposed situations.
- Sharp sand (or a blend) — the aggregate. Use a well-graded, clean sharp sand. For heritage work, try to match the colour and texture of the original sand as closely as possible.
- Water — added sparingly. Lime mortars should be mixed stiff, not sloppy.
Avoid adding Portland cement unless you have specific technical advice to do so — even small amounts significantly increase rigidity.
Typical Mix Ratios
The standard starting point for repointing with lime putty is:
| Situation | Lime Putty | Sharp Sand |
|---|---|---|
| Sheltered, soft brick | 1 part | 2–2.5 parts |
| Exposed or harder brick | 1 part | 2.5–3 parts |
If using natural hydraulic lime (NHL 3.5) in powder form:
| Situation | NHL 3.5 | Sand |
|---|---|---|
| General repointing | 1 part | 2.5–3 parts |
Always follow the manufacturer's specific guidance, as products vary. Suppliers such as Placemakers and Mitre 10 stock lime products, though for heritage-grade materials you may need a specialist masonry supplier.
Step-by-Step: Mixing Lime Mortar
1. Gather Your Materials and Tools
- Lime putty or bagged NHL lime
- Sharp sand (dry or damp — not wet)
- Clean mixing bucket or spot board
- Margin trowel and mixing paddle (or drill with paddle attachment)
- Measuring containers (buckets work well)
- PPE: gloves, safety glasses, and a dust mask (lime is caustic)
2. Measure Your Proportions
Measure lime and sand by volume, not weight. Use the same container for each component to keep ratios consistent.
3. Mix Dry Ingredients First (NHL only)
If using NHL powder, combine the lime and sand dry before adding water. With lime putty, you can combine putty and sand directly.
4. Add Water Gradually
Add clean water a little at a time, mixing thoroughly between additions. The final consistency should be firm and workable — it should hold its shape when squeezed but not crumble. Lime mortar is typically stiffer than cement mortar.
5. Rest the Mix (Lime Putty)
If using lime putty mortar, allow the mixed mortar to rest (slake) for at least 30–60 minutes before use, then re-mix. This improves workability significantly. NHL mortars should be used within about an hour of mixing.
6. Test Before Committing
Apply a small test patch in an inconspicuous area and allow it to cure. Check the colour match and hardness before proceeding with the full job.
Preparing the Joints Before Repointing
Rake out the old mortar to a minimum depth of 15–20 mm using a plugging chisel and hammer, or an angle grinder with a mortar raking disc (take great care not to damage brick faces). Brush out dust and dampen the joint with clean water before applying new mortar — this prevents the dry brick from drawing moisture out of the mortar too quickly, which weakens the bond.
Curing and Aftercare
Lime mortar cures slowly through carbonation (reacting with CO₂ in the air), not by drying out. Keep freshly pointed joints damp for several days in hot or windy weather by misting with water or covering with damp hessian. Avoid repointing in frosty conditions — lime mortar is vulnerable to frost damage before it has fully cured.
When to Call a Professional
For small areas of repointing on a stable wall, a careful DIYer can do a good job. However, you should engage a qualified bricklayer or stonemason if:
- The wall shows signs of structural movement, bulging, or significant cracking
- You're working at height (scaffolding and working-at-height rules under WorkSafe NZ apply)
- The home is heritage-listed or subject to a heritage overlay — councils and Heritage New Zealand may have specific requirements
- You're unsure about the original mortar composition or brick type
- The area to be repointed is large
Repointing done incorrectly is costly to fix and can accelerate brick deterioration. A skilled bricklayer will also be able to assess whether any underlying issues — such as rising damp or structural movement — need addressing first. You can find qualified local bricklayers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
