Repairing crumbling mortar joints — a process called repointing — is one of the more achievable DIY masonry jobs around the home. With the right tools, a suitable mortar mix, and a bit of patience, most homeowners can tackle a garden wall repair over a weekend and have it looking tidy for years to come.
Why Mortar Joints Crumble
NZ's variable climate — freeze-thaw cycles in colder regions, driving rain on the west coast, and UV exposure everywhere — gradually breaks down mortar. Water gets into hairline cracks, expands when it freezes, and slowly pushes the mortar apart. Left untreated, crumbling joints allow moisture into the wall core, which can destabilise the brickwork over time. Catching it early makes the repair far simpler.
Tools and Materials You'll Need
- Cold chisel (plugging chisel) and club hammer
- Angle grinder with a mortar-raking disc (optional but speeds things up)
- Wire brush and stiff-bristled brush
- Pointing trowel and margin trowel
- Jointing tool or a piece of bent copper pipe for finishing
- Safety glasses, dust mask (P2 rated), and gloves — old mortar dust can contain silica
- Mortar mix (see below)
- Spray bottle with water
- Bucket and mixing paddle or a small electric mixer
Choosing the Right Mortar Mix
This is the most critical step. Using a mortar that is too strong (too much cement) can damage the bricks. The mortar in a garden wall should be slightly weaker than the bricks themselves so that any movement causes the mortar — not the brick — to crack. For most NZ garden brick walls, a mix of 1 part cement : 1 part lime : 6 parts sand (by volume) is a good general-purpose repointing mortar. If the existing mortar is a softer, older lime-based type, lean toward more lime and less cement.
Pre-mixed repointing mortars are available in bags from hardware stores and are a convenient option for smaller jobs — just check the bag for the intended application and strength rating. Match the colour to your existing mortar as closely as you can; you may need to experiment with small test batches.
BRANZ is a great resource if you want to dig deeper into mortar specifications and masonry best practice.
Step-by-Step Repointing Process
1. Rake Out the Old Mortar
Using your cold chisel and club hammer (or an angle grinder with a raking disc), carefully remove the crumbling mortar to a depth of at least 15–20 mm. Work along horizontal (bed) joints first, then vertical (perpend) joints. Be firm but controlled — you don't want to chip the brick faces. Wear your safety glasses and P2 dust mask throughout; silica dust is a serious respiratory hazard. See WorkSafe NZ for guidance on working safely with masonry dust.
2. Clean the Joints
Brush out all loose debris with a wire brush, then blow or brush away dust. Lightly dampen the joints with a spray bottle — this stops the dry brick from sucking moisture out of the fresh mortar too quickly, which weakens the bond.
3. Mix Your Mortar
Mix only as much mortar as you can use in about 30–45 minutes. Add water gradually until you reach a firm, peanut-butter consistency — it should hold its shape when squeezed but not be crumbly or sloppy. Let it slake (rest) for 5 minutes, then give it a final mix.
4. Apply the Mortar
Load a small amount of mortar onto your margin trowel and press it firmly into the joint using the pointing trowel. Work in layers if the joint is deep — fill to about half depth, let it firm up slightly, then apply the second layer. Pack the mortar in well to avoid air pockets. Fill horizontal joints before vertical ones.
5. Finish the Joints
Once the mortar has started to stiffen (it should leave a thumbprint but not smear), use your jointing tool or bent pipe to tool the joint to match the existing profile. Common profiles include weatherstruck (angled to shed water — good for NZ conditions), flush, or recessed. Tooling compresses the mortar surface and improves weather resistance.
6. Clean Up and Cure
Brush off any mortar smears from the brick faces with a damp brush before they harden fully. Keep the repaired area damp for 2–3 days by misting with water, especially in hot or windy weather — this slow curing produces stronger mortar. Avoid working in direct hot sun or when frost is forecast.
Matching the Mortar Colour
Getting a colour match can be tricky. Try adding a small amount of oxide pigment to your mix, or test a few small batches and let them dry fully before comparing — mortar lightens significantly as it dries. Accept that a perfect match may not be possible on older walls.
When to Call a Professional
Repointing a small section of garden wall is generally exempt from building consent under Schedule 1 of the Building Act, but always confirm with your local council if you're unsure — especially for larger or structural walls. Consider calling a qualified stonemason or bricklayer (you can find local trades on tradedirectory.co.nz) if:
- The wall is leaning, bulging, or structurally unstable — this is beyond repointing and could be dangerous
- Large sections of mortar are failing across the whole wall
- The wall is heritage or character brick where the wrong mortar could cause irreversible damage
- You're unsure about the correct mortar specification
For any work near electrical cables, gas lines, or plumbing buried close to the wall, contact the relevant licensed professional before digging or grinding. Electrical work must be carried out by a registered electrician (EWRB) and gas work by a licensed gasfitter (PGDB).
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