Waterproofing a brick garden wall is a straightforward DIY job that can significantly extend the life of your brickwork. In New Zealand's variable climate — from Auckland's humid summers to the South Island's frosty winters — moisture is one of the biggest threats to brick and mortar, causing spalling, efflorescence, and structural weakening over time. The good news is that with the right preparation and products, you can tackle this yourself in a weekend.
Why Moisture Damages Brick Walls
Brick is a naturally porous material. When water soaks in and then freezes, expands, or evaporates repeatedly, it breaks down the brick face and mortar joints — a process called spalling. You may also notice white powdery deposits called efflorescence, which is salt drawn to the surface by moisture movement. Left untreated, this can lead to crumbling mortar, loose bricks, and costly repairs. BRANZ notes that moisture management is one of the most critical factors in the longevity of masonry construction in NZ.
Assess the Wall First
Before applying any waterproofing product, inspect the wall carefully:
- Check mortar joints for cracks, gaps, or crumbling sections. Any damaged mortar must be raked out and repointed before waterproofing — sealing over damaged joints traps moisture inside.
- Look for existing cracks in the bricks themselves. Hairline cracks can be sealed; larger structural cracks may need a professional assessment.
- Check drainage at the base of the wall. Poor drainage means water will pool and undermine your waterproofing efforts regardless of what product you use.
- Identify efflorescence. If present, clean it off with a stiff brush and a diluted masonry cleaner before proceeding.
Repair Before You Waterproof
This step is non-negotiable. Use a mortar mix suitable for exterior masonry — products are available at Bunnings or Mitre 10. Rake out loose mortar to a depth of at least 15 mm, dampen the joint, and press in fresh mortar. Allow it to cure fully (typically 7–28 days depending on conditions and product) before applying any waterproofing treatment.
For larger crack repairs or structural concerns, Sika offers a range of masonry repair products well suited to NZ conditions.
Choosing the Right Waterproofing Product
There are two main approaches for garden walls:
| Product Type | How It Works | Best For |
|---|---|---|
| Penetrating silane/siloxane sealer | Soaks into the brick and repels water while allowing the wall to breathe | Most brick garden walls — preserves natural look |
| Film-forming masonry sealer | Creates a surface coating that blocks water | Walls needing extra protection; changes appearance slightly |
For most NZ garden walls, a penetrating silane or siloxane-based sealer is the preferred choice. These products allow water vapour to escape (breathability is important — trapping moisture inside is worse than leaving the wall unsealed), while preventing liquid water from entering. Look for products labelled as masonry water repellent or brick sealer at your local hardware store.
Resene and Dulux both stock masonry sealers and waterproofing products suitable for exterior brickwork. Always read the product datasheet and confirm it is rated for exterior, below-ground-level, or exposed use as appropriate for your situation.
Step-by-Step Application
1. Clean the Wall Thoroughly
Remove dirt, moss, lichen, and efflorescence. A stiff brush and garden hose works for light soiling. For moss or algae, use a diluted masonry cleaner or a product containing a biocide. Allow the wall to dry completely — most sealers require the surface to be dry before application.
2. Mask Off Surrounding Areas
Protect garden beds, paving, and any adjacent surfaces with drop sheets or masking tape. Sealers can be slippery on paving if overspray occurs.
3. Apply the Sealer
Apply with a low-pressure garden sprayer, roller, or wide brush depending on the product instructions. Work from the bottom up to avoid streaking. Apply generously enough that the product soaks in rather than sitting on the surface. Most penetrating sealers require two coats, with the second applied while the first is still slightly tacky (wet-on-wet) — check your product's instructions carefully as timing varies.
4. Allow to Cure
Keep the wall dry during the curing period — typically 24–48 hours minimum. Avoid applying if rain is forecast or if temperatures are below 10°C, as this affects curing.
5. Reapply Periodically
Penetrating sealers typically last 5–10 years depending on exposure and product quality. Inspect the wall annually and reapply when water no longer beads on the surface.
Additional Tips for NZ Conditions
- In high-rainfall regions (West Coast, Northland, Wellington), consider applying sealer more frequently or using a higher-grade product.
- Ensure the coping (the cap on top of the wall) is in good condition and sheds water away from the wall face. A damaged or missing coping is a major source of moisture ingress.
- Check that weep holes (if present in retaining walls) are clear and functioning.
- For walls near coastal areas, salt spray can accelerate deterioration — choose a sealer specifically rated for coastal exposure.
When to Call a Professional
While waterproofing a garden wall is generally DIY-friendly, call a qualified bricklayer or stonemason if:
- You notice significant structural cracking, leaning, or bulging in the wall
- The wall is a retaining wall holding back soil — these have structural and drainage requirements under the NZ Building Code and may require a building consent depending on height
- Mortar deterioration is widespread and the wall needs extensive repointing
- You're unsure whether the wall is safe to work on
Retaining walls over a certain height typically require a building consent — check with your local council for the applicable threshold, as requirements can vary depending on the wall's location and the soil conditions it retains — always check with your local council before carrying out significant work. You can find qualified local bricklayers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
