Mixing mortar correctly is the key to a brick repair that holds up to New Zealand's variable weather. For most small domestic brick repairs, a 1:4 or 1:5 cement-to-sand ratio (by volume) is the standard starting point — though matching the strength and colour of your existing mortar matters just as much as the mix itself.
What You'll Need
Before you start, gather the following:
- Portland cement (general purpose, available at Bunnings or Mitre 10)
- Bricklaying sand (also called soft sand or plasterer's sand — not sharp/concreting sand)
- Clean, potable water — never use seawater or dirty water
- A mixing board or bucket (for small jobs, a bucket is fine)
- A margin trowel or pointing trowel
- Safety gloves and eye protection — wet cement is caustic
- Optional: lime (hydrated builder's lime) to improve workability
Understanding Mortar Ratios
The mix ratio controls the strength and flexibility of your mortar. Using too much cement makes mortar brittle and prone to cracking; too little makes it weak.
| Application | Cement : Sand | Lime (optional) |
|---|---|---|
| General brickwork repair | 1 : 4 | — |
| Softer/older bricks | 1 : 5 | Add 0.5 parts lime |
| Exposed or high-traffic areas | 1 : 3 | — |
| Heritage or soft clay bricks | Lime mortar only | Specialist product |
Important: Older NZ homes — particularly villas and bungalows built before the 1950s — often used lime-based mortars. Repointing these with a strong Portland cement mix can trap moisture and damage the bricks. If you're unsure about your brick type, consult a qualified bricklayer before proceeding.
Step-by-Step Mixing Instructions
1. Measure Your Materials
Use a consistent measure — a small bucket, a coffee tin, or a trowel count. For a small repair, try 1 part cement to 4 parts bricklaying sand. Mix dry ingredients thoroughly before adding water.
2. Combine Dry Ingredients
Tip the sand into your bucket or onto a mixing board first, then add the cement on top. Mix them together dry until the colour is uniform — no streaks of grey or yellow.
3. Add Water Gradually
Make a well in the centre and add small amounts of clean water, mixing as you go. You're aiming for a firm, workable consistency — the mortar should hold its shape when squeezed in your gloved hand and not slump or crumble. A common mistake is adding too much water, which weakens the mix.
4. Check the Consistency
Push your trowel into the mix and pull it out — the mortar should leave a clean edge and not be runny. It should slide off the trowel slowly, not pour off.
5. Mix Only What You Can Use
Fresh mortar has a working life of roughly 1–2 hours depending on temperature and humidity. In hot, dry NZ summers, it can go off faster. Mix small batches and don't add water to mortar that has started to stiffen — discard it and mix fresh.
Colour Matching Your Existing Mortar
One of the trickiest parts of any brick repair is matching the colour of the existing mortar joints. Wet mortar always looks darker than cured mortar, so test a small patch and let it dry fully before committing to a large area. You can use mortar pigments/dyes (available at most hardware stores) to adjust the colour. Take a photo or a sample of your existing mortar to the store for comparison.
Preparing the Joint Before Applying Mortar
Good preparation is just as important as the mix itself:
- Rake out the old, damaged mortar to a depth of at least 15–20 mm using a cold chisel and hammer or an angle grinder with a mortar-raking disc
- Brush out all dust and loose material
- Dampen the joint and surrounding bricks with water before applying new mortar — this stops the dry brick from sucking moisture out of the mix too quickly, which causes weak bonding
Safety Notes
Wet cement is alkaline and caustic — always wear gloves and safety glasses. If cement contacts skin, rinse immediately with clean water. For dust exposure when mixing or raking, wear a P2 dust mask. WorkSafe NZ has guidance on working safely with construction materials.
When to Call a Professional
While mixing mortar and repointing small areas is well within a capable DIYer's reach, there are situations where you should bring in a qualified bricklayer:
- Widespread mortar failure or cracking across a large area
- Structural brickwork (retaining walls, load-bearing walls, chimneys) — this work may require a building consent and must comply with the NZ Building Code
- Heritage or soft clay bricks requiring specialist lime mortars
- Any repair where you're unsure whether the brickwork is structurally sound
For chimney repairs in particular, note that work near flues may intersect with restricted gas or fire appliance work — always check with your local council and relevant licensed tradespeople.
You can find qualified, local bricklayers on tradedirectory.co.nz to get the job done right.
Licensed Building Practitioner (LBP)
