Water leaking through a brick wall is a frustrating but very common problem in New Zealand, particularly in older homes and in regions with high rainfall or driving winds. The good news is that many causes can be identified and fixed with the right approach — though some situations do require a qualified waterproofer or builder.
Why Does Water Leak Through Brick Walls?
Brick itself is a porous material, and over time mortar joints crack, erode, or pull away from the bricks. In NZ's variable climate — from Auckland's humid summers to Wellington's wind-driven rain — these gaps become pathways for moisture. Common causes include:
- Cracked or eroded mortar joints (the most frequent culprit)
- Cracked or spalling bricks caused by freeze-thaw cycles in colder regions
- Failed or missing sealant around windows, doors, and penetrations
- Blocked or missing weep holes in cavity brick construction
- Rising damp from the ground if damp-proof courses have failed
- Inadequate or failed flashings at parapets, sills, or roof junctions
- No cavity in older solid-brick construction, meaning water has a direct path inside
Step 1 — Find the Source Before You Fix Anything
Before reaching for a sealant, spend time locating exactly where the water is entering. Wet the wall with a hose from the outside while someone watches inside — start low and work upward. Water often travels before it appears, so the wet patch inside may not be directly behind the entry point outside.
Check:
- Mortar joints (run your finger along them — crumbling mortar is a giveaway)
- Window and door sills and their sealant beads
- Flashings at the top of the wall or parapet
- Weep holes (small gaps left at the base of cavity walls to allow drainage — these must stay clear, not be blocked)
Step 2 — Repoint Cracked Mortar Joints
Repointing (also called tuck-pointing) is the process of raking out old, damaged mortar and replacing it with fresh mortar. This is one of the most effective DIY repairs for leaking brick walls.
How to repoint:
- Use a cold chisel and hammer (or an angle grinder with a mortar-raking disc) to remove loose mortar to a depth of at least 15–20 mm.
- Brush out dust and dampen the joint.
- Mix a suitable mortar — for most NZ brick walls a 1:1:6 (cement:lime:sand) mix is appropriate, but check the original mortar hardness; using a mix that is too hard can cause bricks to crack.
- Press the new mortar firmly into the joint and finish to match the existing profile.
- Keep the repair damp for a couple of days to cure properly.
For small areas this is a manageable DIY job. For large sections of wall, consider hiring a qualified bricklayer or waterproofer — find one on tradedirectory.co.nz.
Step 3 — Reseal Around Openings and Penetrations
Silicone or polyurethane sealant around windows, doors, pipes, and other penetrations degrades over time. Remove old sealant completely with a sealant remover tool, clean the surface, and apply a fresh bead of a quality exterior-grade sealant. Products from Sika are widely used in NZ for this purpose. Make sure the sealant is compatible with masonry and rated for exterior use.
Step 4 — Apply a Masonry Waterproofing Sealer
Once mortar and sealant repairs are done, a penetrating masonry sealer or water-repellent treatment can be applied to the entire wall face to reduce water absorption. These products soak into the brick and mortar, repelling water while still allowing the wall to breathe (which is important to avoid trapping moisture inside).
Look for silane- or siloxane-based penetrating sealers at Bunnings or Mitre 10. Always follow the manufacturer's instructions — surface preparation and dry conditions at application are critical. Avoid film-forming sealers that sit on the surface, as these can trap moisture and cause spalling.
Resene also offers masonry waterproofing coatings if a painted finish is acceptable for your wall.
Step 5 — Check Flashings and Drainage
If water is entering at the top of the wall, at a parapet, or where the wall meets the roof, flashings are likely the issue. Flashings are metal (usually aluminium or zinc) or flexible membrane strips that direct water away from junctions. Damaged or missing flashings are a significant leak source and often require a qualified tradesperson to repair correctly — particularly where they connect to roofing.
Also check that weep holes at the base of cavity walls are clear. Never block these — they are essential for draining any water that gets into the cavity.
NZ Building Code Considerations
If your repairs are substantial — for example, replacing flashings, altering the wall structure, or addressing rising damp with a new damp-proof course — you may need a building consent. Minor like-for-like repairs such as repointing and resealing generally fall under Schedule 1 exemptions, but always confirm with your local council before starting work. For guidance, visit MBIE Building Performance.
For rental properties, landlords should also be aware of Healthy Homes Standards, which require rental homes to be free from moisture and dampness issues. See Tenancy Services for details.
When to Call a Professional
Call a licensed waterproofer, builder, or Licensed Building Practitioner (LBP) if:
- The leak source is unclear after investigation
- There is significant structural cracking in the brickwork
- Rising damp is suspected (requires specialist diagnosis and a damp-proof course)
- Flashings need replacing or major repair
- The wall is a solid brick (no cavity) construction — these require specialist waterproofing solutions
- Mould or internal damage is already present
- The property is a rental and you need to meet Healthy Homes obligations
A professional waterproofer will have access to specialist diagnostic tools and commercial-grade products, and can provide a warranty on their work. You can find qualified local waterproofers on tradedirectory.co.nz.
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SiteWise
Licensed Building Practitioner (LBP)
