A brick wall that stays damp after rain is more than just an eyesore — left untreated, moisture ingress can damage interior linings, promote mould growth, and undermine the structural integrity of the wall over time. The good news is that many causes are straightforward to diagnose and, in some cases, a confident DIYer can tackle the repairs themselves.
Why Brick Walls Let in Water
Brick itself is actually quite porous, so most brick walls rely on mortar joints, wall ties, flashings, and sometimes a cavity or waterproof coating to manage moisture. When any of these elements fail, water finds a way in. Common culprits include:
- Deteriorated mortar joints — mortar cracks and erodes over time, especially in exposed or coastal NZ locations
- Cracked or spalled bricks — freeze-thaw cycles and UV exposure cause surface cracking
- Failed or missing flashings — above windows, doors, or at the base of the wall
- Blocked weep holes — these allow moisture in the cavity to drain out; if blocked, water backs up
- No DPC (damp-proof course) — older NZ homes (pre-1960s especially) may lack an effective damp-proof course at the base of the wall
- Missing or degraded waterproof coating — some brick walls rely on a surface sealer that has worn away
Step 1 — Diagnose the Source
Before reaching for the sealant, spend time finding exactly where water is entering. After heavy rain, inspect the wall closely:
- Check mortar joints for cracks, gaps, or crumbling sections — run your finger along them; loose or sandy mortar is a clear sign
- Look for efflorescence (white salt deposits) — this tells you water has been moving through the wall
- Inspect flashings above openings and at wall junctions for gaps, rust, or lifting
- Check weep holes at the base of cavity walls — they should be open and unobstructed
- Look at the ground level — soil or garden beds built up against the wall can bridge the DPC and allow moisture to wick upward
If damp appears on interior walls or ceilings, the issue may be more serious and could involve the wall's cavity or structural elements — at that point, get a professional assessment.
Step 2 — Repointing Mortar Joints
Repointing (also called tuckpointing) is the most common fix for a leaking brick wall. It involves raking out the old, failed mortar and replacing it with fresh mortar.
What you'll need
- Cold chisel and club hammer (or an angle grinder with a mortar-raking disc)
- Stiff brush
- Pre-mixed mortar or a sand-and-cement mix (check the original mortar hardness — using a mix that's too hard can crack softer bricks)
- Pointing trowel or jointing tool
- Safety glasses and dust mask — WorkSafe NZ notes that old mortar dust can contain silica, so respiratory protection is essential
How to repoint
- Rake out old mortar to a depth of at least 15–20 mm
- Brush out all loose debris and dampen the joint with water
- Press fresh mortar firmly into the joint in layers if deep
- Tool the joint to match the original profile (weathered, flush, or recessed)
- Keep the repair damp for a couple of days to cure properly
Match the mortar strength to your bricks — softer heritage bricks need a lime-based mortar, not a strong cement mix, or you risk cracking the bricks themselves. If you're unsure, ask at PlaceMakers or Mitre 10 for advice on the right product.
Step 3 — Repair or Replace Damaged Bricks
Spalled or cracked bricks should be carefully removed with a chisel and replaced. Matching the brick colour and texture can be tricky on older NZ homes — check salvage yards or ask your supplier. Bed the new brick in mortar, allow it to set, then repoint the surrounding joints.
Step 4 — Check and Repair Flashings
Flashings above windows, doors, and at wall-to-roof junctions are critical. In NZ, Clause E2 of the NZ Building Code sets out requirements for managing external moisture. If flashings are corroded, lifted, or missing, water will pour straight in regardless of how good your mortar is. Minor flashing repairs (re-bedding a lifted section with appropriate sealant) can be DIY, but significant flashing replacement — especially where it ties into roofing — is best left to a professional. BRANZ has excellent guidance on weathertightness details.
Step 5 — Apply a Brick Sealer or Water Repellent
Once mortar and bricks are sound, a penetrating water repellent (also called a masonry sealer or silane/siloxane treatment) can significantly reduce moisture absorption without changing the wall's appearance. These products allow the wall to breathe while repelling liquid water.
- Clean the wall thoroughly and allow it to dry completely before applying
- Follow the manufacturer's instructions carefully
- Avoid film-forming sealers on cavity walls — they can trap moisture inside
Resene and Dulux both offer masonry waterproofing products suitable for NZ conditions.
NZ-Specific Considerations
- Healthy Homes Standards require rental properties to be free from moisture and dampness issues — landlords have legal obligations. See Tenancy Services for details.
- Building consent is generally not required for like-for-like mortar repairs or sealing, but if you're making structural changes to a wall, check with your local council. MBIE Building Performance outlines Schedule 1 exemptions.
- NZ's varied climate — from the wet West Coast to the salty coastal north — means the right product choice matters. Ask suppliers for products suited to your region.
When to Call a Professional
Call a licensed bricklayer if:
- The damp is widespread or the mortar is failing across large sections of the wall
- You suspect structural cracking or wall tie failure
- The DPC is absent or has failed (rising damp from the base)
- Flashings need significant replacement
- Interior damage (mould, wet linings, rotting framing) suggests moisture has been entering for some time
A qualified bricklayer can assess the full extent of the problem and carry out repairs to a standard that meets the NZ Building Code. You can find experienced local bricklayers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
