Spalling — where the face of a brick flakes, chips, or crumbles away — is a common problem in older New Zealand homes, particularly those built before the 1970s. The good news is that minor spalling can often be repaired as a DIY project, but more widespread damage usually calls for a qualified bricklayer to assess and fix the underlying cause before it gets worse.
What Causes Brick Spalling?
Understanding the cause is essential before you start any repair, otherwise the problem will return. Common causes in NZ include:
- Moisture penetration — water soaks into the brick, then freezes and expands in cold snaps (common in southern and elevated regions), forcing the face apart
- Salt crystallisation (efflorescence) — salts dissolved in water migrate to the surface and crystallise, pushing the face off from within
- Inappropriate sealers or paints — trapping moisture inside the brick rather than letting it breathe
- Age and weathering — older, softer bricks simply wear out over time
- Incorrect mortar — mortar that is harder than the brick forces movement stress into the brick face rather than the joint
If you notice white powdery deposits (efflorescence), damp patches, or crumbling mortar alongside the spalling, address moisture ingress first. Check gutters, downpipes, flashings, and damp-proof courses before patching.
Assessing the Damage
Before reaching for the trowel, tap each affected brick gently with a small hammer. A hollow sound means the face has delaminated and is likely to fall away soon. Rate the damage:
| Severity | Description | Likely repair |
|---|---|---|
| Minor | Surface flaking, face mostly intact | Consolidant + mortar patch |
| Moderate | Face partially missing, brick still sound | Mortar patch or spall repair mortar |
| Severe | Brick crumbling, hollow, or broken through | Full brick replacement |
| Widespread | Multiple bricks across a large area | Call a bricklayer |
Tools and Materials You'll Need
- Safety glasses, dust mask (P2 rated), and gloves
- Wire brush and stiff-bristle brush
- Cold chisel and club hammer
- Brick consolidant / stabiliser (available at Bunnings or Mitre 10)
- Pre-mixed brick repair mortar or colour-matched mortar mix
- Pointing trowel and margin trowel
- Spray bottle with water
- Replacement bricks (if needed — try to match the original)
Step-by-Step: Patching a Spalled Brick Face
1. Clean the Area
Use a wire brush to remove all loose material, dust, and flaking pieces. Don't use a pressure washer directly on spalled bricks — it can drive water deeper and worsen the damage.
2. Apply a Brick Consolidant
For soft or crumbling surfaces, apply a brick consolidant (sometimes called a stabiliser or hardener) to the exposed area. This penetrates and binds loose particles, giving the repair mortar something solid to grip. Follow the manufacturer's drying time — usually several hours.
3. Dampen the Surface
Lightly mist the repair area with water before applying mortar. This prevents the dry brick from sucking moisture out of the patch too quickly, which causes cracking.
4. Mix and Apply Repair Mortar
Use a pre-mixed brick repair mortar or mix your own using a lime-based mortar (1 part cement : 1 part lime : 6 parts sand is a common mix for older soft bricks). Avoid using a strong Portland cement-only mix on older bricks — it can be too rigid and cause further spalling.
Press the mortar firmly into the void with a pointing trowel, building up in layers no more than 10–15 mm thick if the void is deep. Feather the edges to blend with the surrounding brick face.
5. Texture and Colour Match
While the mortar is still slightly soft, use a damp sponge or brush to texture the surface to match the surrounding brick. Colour-matching can be tricky — test a small area first and allow it to dry fully before judging the colour, as mortar lightens significantly as it cures.
6. Cure Slowly
Keep the repair damp for 2–3 days by misting it lightly or covering with damp hessian. Avoid working in direct hot sun or strong wind, which dry the mortar too fast.
Full Brick Replacement
If a brick is hollow, broken through, or structurally compromised, it needs to be replaced entirely. This involves carefully cutting out the old mortar joints with an angle grinder or plugging chisel, removing the damaged brick, and bedding in a matching replacement. This is more involved and, if the wall is structural or part of a load-bearing system, you should have a qualified bricklayer carry out the work. Check whether your project requires a building consent — MBIE Building Performance has guidance on Schedule 1 exemptions, but always confirm with your local council.
Preventing Future Spalling
- Keep mortar joints in good condition — repoint any gaps before water gets in
- Ensure gutters and downpipes direct water well away from brickwork
- Avoid painting or sealing bricks with non-breathable coatings
- If you do want to seal brickwork, use a breathable silane/siloxane-based water repellent rather than a film-forming sealer
- BRANZ has excellent technical guidance on masonry maintenance for NZ conditions
When to Call a Professional
Call a qualified bricklayer if:
- More than a handful of bricks are affected
- The damage is on a structural or load-bearing wall
- You suspect ongoing moisture ingress that you can't identify the source of
- The brickwork is part of a heritage or character home where matching materials matter
- You're unsure whether a building consent is required
A licensed bricklayer can also advise on whether the original mortar specification was correct for your brick type — a common hidden cause of spalling. You can find experienced local bricklayers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
