How to Repair a Brick Wall Damaged by Tree Roots

Tree roots are surprisingly powerful — they can crack mortar joints, push bricks out of alignment, and even undermine a wall's foundations over time. The good news is that many root-damaged brick walls can be repaired by a competent DIYer or bricklayer, provided the structural damage isn't too severe. Here's how to assess, repair, and protect your brick wall.

Step 1: Assess the Damage Before You Start

Before picking up a trowel, take a careful look at the full extent of the damage. Root damage typically falls into one of three categories:

• Minor mortar damage – cracked or missing mortar joints, with bricks still in place
• Moderate displacement – bricks pushed out of line, cracked bricks, but the wall is still standing
• Severe structural damage – sections of wall leaning, collapsed, or with foundations visibly undermined

For minor to moderate damage, a confident DIYer can often handle repairs. Severe structural damage — especially to a retaining wall or a wall close to your home's foundation — should be assessed by a qualified bricklayer or structural engineer before any work begins. Retaining walls over 1.5 metres high typically require a building consent under the NZ Building Code; always check with your local council before starting significant repairs or rebuilding.

Step 2: Deal With the Tree Roots First

Repairing the wall without addressing the root cause (literally) is a waste of time and money. You have two main options:

• Remove the tree or shrub – the most permanent solution. Once the tree is gone, the roots will gradually die and stop exerting pressure. Note that some trees in NZ are protected under district plans, so check with your council before removing any tree.
• Root barrier installation – if you want to keep the tree, a physical root barrier (a rigid plastic or geotextile sheet buried vertically in the soil) can redirect roots away from the wall. These are available from garden centres and some hardware stores.

Avoid using chemical root killers near brick walls, as they can affect soil stability and nearby plants.

Step 3: Gather Your Tools and Materials

For most brick wall repairs you'll need:

• Cold chisel and club hammer
• Angle grinder with a mortar-raking disc (for stubborn joints)
• Stiff brush and vacuum
• Pointing trowel and hawk
• Pre-mixed or bagged mortar (match the existing mix — see below)
• Replacement bricks (try to match colour and size)
• Safety glasses, dust mask (P2 rated), and gloves

Mortar matching is critical. Using a mortar that is too hard (high cement content) on older brick walls can cause bricks to crack as the wall moves. Older NZ brick walls often used a lime-based mortar. If you're unsure, take a sample to your local PlaceMakers or Mitre 10 branch for advice, or consult BRANZ guidance on mortar selection.

Step 4: Remove Damaged Mortar and Bricks

1. Using a cold chisel and club hammer (or an angle grinder with a raking disc), carefully remove all cracked, crumbling, or root-disturbed mortar to a depth of at least 15–20 mm.
2. Remove any cracked or displaced bricks by chiselling out the surrounding mortar. Work carefully to avoid damaging sound bricks nearby.
3. Brush and vacuum out all loose debris from the joints and cavities.

Safety note: Brick dust contains silica, which is hazardous to lungs. Always wear a P2 dust mask and safety glasses. Review WorkSafe NZ guidelines on working with silica dust.

Step 5: Repoint the Mortar Joints

Repointing is the process of filling cleaned-out joints with fresh mortar. This is the most common repair for root-damaged walls.

1. Dampen the joint area lightly with water — this stops the brick from drawing moisture out of the mortar too quickly.
2. Mix your mortar to a firm, workable consistency (follow the bag instructions).
3. Pack mortar firmly into the joint using a pointing trowel, working in layers if the joint is deep.
4. Finish the joint to match the existing profile (flush, recessed, or weathered).
5. Allow to cure slowly — avoid direct sun or frost for the first 24–48 hours.

Step 6: Replace Damaged Bricks

If bricks are cracked or badly displaced:

1. Bed replacement bricks on fresh mortar, checking they are level and aligned with the surrounding courses.
2. Fill all surrounding joints with mortar and point to match.
3. Allow the repair to cure fully before applying any sealant or paint.

If you need to source matching bricks, try local demolition yards or brick suppliers — NZ brick sizes and colours vary by region and era, so an exact match isn't always possible.

Step 7: Check and Repair the Foundation

If roots have undermined the wall's base, the footing may need to be reinstated. This is specialist work — a bricklayer or structural engineer should assess whether the footing is adequate before you rebuild any section of wall. Refer to MBIE Building Performance for guidance on when consent is required.

When to Call a Professional

Call a qualified bricklayer or structural engineer if:

• The wall is leaning, bulging, or has collapsed
• The damage affects a retaining wall over 1.5 m high
• The wall is part of your home's structure (e.g., a house wall or chimney)
• You suspect the foundations have been significantly undermined
• You're unsure about mortar type or structural integrity

A licensed bricklayer will ensure repairs meet the NZ Building Code and will last. You can find qualified local bricklayers on tradedirectory.co.nz.

Sources & Further Reading

• BRANZ – Building Research Association of NZ
• MBIE Building Performance – NZ Building Code guidance
• WorkSafe NZ – Silica dust safety
• Mitre 10 – Tools and materials
• PlaceMakers – Building supplies
• Standards NZ – NZS 3604 and related standards