How to Repair a Cracked Brick Chimney Safely from a Ladder

Minor cracks in a brick chimney are common in New Zealand, especially after seismic activity or years of weathering. Many small mortar joint cracks can be repaired by a confident DIYer working safely from a ladder — but it's important to know your limits before you climb up.

Assess the Damage First (From the Ground)

Before you set up a ladder, use binoculars to inspect the chimney from the ground. This helps you understand the scope of the job without unnecessary risk.

Look for:

• Hairline cracks in mortar joints — usually a straightforward DIY repoint
• Cracked or spalling bricks — may need individual bricks replaced
• Cracks running through bricks themselves — a sign of structural movement; get a professional assessment
• Leaning or bulging sections — do not climb near this; call a bricklayer immediately
• Damaged flashing or cap — often the source of water ingress

If the chimney shows signs of significant structural movement — particularly relevant in earthquake-prone NZ regions — contact a Licensed Building Practitioner (LBP) before doing anything. Check www.lbp.govt.nz to find one.

Ladder Safety: Non-Negotiable

Working at height is one of the leading causes of serious injury in New Zealand. WorkSafe NZ has clear guidance on working safely from ladders.

Key rules:

• Use a fibreglass or aluminium extension ladder rated to hold your weight plus tools
• Set the ladder at a 4:1 ratio — for every 4 metres of height, the base sits 1 metre out from the wall
• Secure the top of the ladder with a ladder standoff bracket so it doesn't rest against the chimney itself (which can be fragile)
• Always have a second person on the ground to foot the ladder and pass materials
• Wear non-slip footwear and keep your hips between the rails at all times
• Never overreach — move the ladder instead
• Do not work on a ladder in high winds or wet conditions — NZ weather can change quickly

If the chimney is above the roofline by more than a metre or two, or if your roof pitch makes ladder access awkward, seriously consider hiring a professional with proper scaffolding.

Tools and Materials You'll Need

• Cold chisel and club hammer (for raking out old mortar)
• Wire brush
• Pointing trowel or mortar gun
• Bucket and mixing paddle (or pre-mixed mortar)
• Exterior-grade mortar mix suitable for chimneys (check your local Bunnings or Mitre 10)
• Safety glasses, dust mask (P2 rated), and gloves
• Sponge and water for finishing

Choosing the Right Mortar

This is critical. Old NZ brick chimneys — particularly those built before the 1980s — often used a soft lime-based mortar. Using a modern Portland cement mortar that is too hard can cause the bricks themselves to crack over time, as the mortar won't flex with the brick. If you're unsure what mortar was originally used, consult a bricklayer or check with BRANZ for guidance on heritage materials. A general-purpose lime-sand mortar is often a safer choice for older chimneys.

Products from Sika include pre-mixed repair mortars suitable for masonry — read the datasheet carefully to confirm suitability for chimneys.

Step-by-Step: Repointing Cracked Mortar Joints

1. Rake out the old mortar to a depth of at least 15–20 mm using a cold chisel and hammer. Don't go deeper than needed.
2. Brush out all dust and loose material with a wire brush.
3. Dampen the joint lightly with water — this stops the brick from drawing moisture out of the fresh mortar too quickly.
4. Mix your mortar to a firm, workable consistency (like peanut butter).
5. Press mortar firmly into the joint using a pointing trowel, working in small sections.
6. Tool the joint to match the existing profile (usually a slightly recessed or flush finish on chimneys).
7. Keep the repair damp for 24–48 hours by misting with water — this helps the mortar cure properly, especially in hot or windy NZ conditions.

Chimney Cap and Flashing

If the chimney cap (the mortar or concrete crown on top) is cracked, this is a major source of water entry and should be repaired or replaced. A cracked cap can be patched with a flexible masonry sealant for minor cracks, or recast entirely for larger damage. Chimney flashing (the metal seal between chimney and roof) is best left to a roofer or bricklayer, as incorrect flashing can breach the weathertight envelope covered under NZ Building Code clause E2.

Building Consent Considerations

Minor like-for-like mortar repairs to a chimney are generally exempt from building consent under Schedule 1 of the Building Act — but always confirm with your local council, as exemptions can depend on the extent of work and your property's specific situation. Guidance is available at MBIE Building Performance.

When to Call a Professional

Call a qualified bricklayer or stonemason if you notice:

• Structural cracks running through bricks (not just mortar joints)
• Any leaning, bulging, or movement in the chimney stack
• Damage above the roofline that requires working on the roof itself
• You're uncomfortable working at height — there's no shame in it
• The chimney is heritage or character brick requiring specialist knowledge

For gas or wood-burning fireplaces, have the flue and firebox inspected by a qualified professional before lighting fires after any repair work. Gas work must only be carried out by a licensed tradesperson registered with the Plumbers Gasfitters & Drainlayers Board.

You can find experienced local bricklayers and chimney repair specialists on tradedirectory.co.nz.

Sources & Further Reading

• WorkSafe NZ – Working at Height
• MBIE Building Performance – Building Act and consents
• BRANZ – Masonry and repair guidance
• Licensed Building Practitioners
• Sika NZ – Masonry repair products
• Mitre 10 NZ – Mortar and masonry supplies