New Zealand's damp climate — especially in regions like the West Coast, Waikato and Wellington — makes brickwork a prime target for mould, moss, lichen and general grime. The good news is that with the right approach, most homeowners can tackle this job themselves. Here's how to do it safely and effectively without damaging your bricks or mortar.
Why Brickwork Gets Dirty So Quickly in NZ
Brick is a porous material, which means it absorbs moisture readily. In shaded or south-facing areas that stay damp, mould and moss can take hold within a single season. Lichen — that crusty, flat growth — is particularly stubborn and can actually etch into the brick surface over time. Beyond aesthetics, unchecked biological growth can accelerate mortar deterioration, so it's worth dealing with promptly.
BRANZ research highlights that moisture management is one of the key factors in maintaining masonry in NZ's variable climate.
What You'll Need
Before you start, gather your supplies:
- Stiff-bristled brush (natural or nylon — avoid wire brushes on softer bricks as they can scratch)
- Garden hose or low-pressure sprayer
- Bucket and sponge
- Safety glasses, rubber gloves, and old clothing
- A purpose-made masonry cleaner or biocide (available at Bunnings or Mitre 10)
- White vinegar (for light mould — a natural option)
- Drop sheets to protect nearby plants and surfaces
Safety note: Always wear eye protection and gloves when working with cleaning chemicals. Work on a dry, overcast day — direct sun can cause cleaners to dry too fast and leave residue.
Step 1 — Inspect the Brickwork First
Before reaching for the hose, take a close look at the mortar joints. If you notice crumbling, cracked or missing mortar, cleaning could drive water deeper into the wall and worsen the damage. In that case, repointing should happen before cleaning. Also check for any efflorescence — the white, chalky salt deposits that sometimes appear on brick — as this needs a different treatment to mould or moss.
Step 2 — Remove Loose Debris
Use a dry stiff brush to sweep away loose moss, dirt and cobwebs. Work from the top of the wall downward so debris falls clear of areas you've already cleaned. For larger areas like garden walls or paths, a leaf blower can speed this up.
Step 3 — Apply Your Cleaning Solution
For mould and mildew, a diluted bleach solution (roughly one part bleach to ten parts water) or a proprietary biocide cleaner works well. Products containing benzalkonium chloride are commonly available at NZ hardware stores and are effective against moss, algae and mould.
For moss and lichen, a dedicated moss killer applied and left to dwell for the time specified on the label will kill the growth before you scrub. Don't rush this step — letting the product work means less elbow grease.
For general dirt and grime, warm water with a small amount of dish soap is often sufficient on its own.
Application tips:
- Wet the brickwork lightly with plain water before applying chemical cleaners — this helps prevent the cleaner soaking too deep into the brick
- Apply the solution generously with a brush or garden sprayer
- Allow the recommended dwell time (check the product label)
- Protect nearby plants by covering them with drop sheets and rinsing any overspray off immediately
Step 4 — Scrub and Rinse
Using your stiff brush, scrub the surface in a circular motion, paying extra attention to mortar joints where mould tends to hide. Rinse thoroughly with clean water, again working top to bottom.
What About Pressure Washing?
Pressure washing can be effective but must be used with caution. High pressure can erode soft mortar joints and damage older or handmade bricks. If you use a pressure washer, keep the pressure low (generally under 1,000 PSI / around 70 bar), use a wide-angle fan nozzle, and hold it at least 300 mm from the surface. Avoid directing the jet straight into mortar joints at close range.
For heritage or older brick buildings, hand scrubbing is always the safer choice.
Step 5 — Consider a Sealer or Inhibitor
Once the brickwork is clean and fully dry (allow several dry days), applying a breathable masonry sealer or biocide inhibitor can slow the return of mould and moss significantly. Look for products labelled as breathable or vapour-permeable — these allow moisture to escape from the brick rather than trapping it inside, which is important for NZ's wet conditions. Sika and other masonry product suppliers offer suitable options.
Comparison: Common Cleaning Methods
| Method | Best For | Risk Level | Cost (Guide Only) |
|---|---|---|---|
| Brush + soapy water | Light dirt, general grime | Low | Very low |
| Diluted bleach solution | Mould, mildew | Low–Medium | Low |
| Proprietary biocide | Moss, algae, lichen | Low–Medium | Low–Medium |
| Pressure washing | Heavy soiling, large areas | Medium | Low–Medium (hire) |
| Professional chemical clean | Severe staining, heritage brick | Low (if done right) | Medium–High |
When to Call a Professional
Some situations are best left to an experienced bricklayer or masonry cleaner:
- Heritage or character brickwork — older bricks are often softer and more easily damaged by aggressive cleaning
- Severe or recurring mould that keeps coming back despite cleaning, which may indicate a moisture or drainage problem behind the wall
- Damaged mortar joints that need repointing before or after cleaning
- Large commercial or multi-storey buildings where working at height creates safety risks
- Efflorescence or deep staining that doesn't respond to standard cleaning
For complex jobs, it's worth getting a qualified bricklayer to assess the wall. You can find experienced local bricklayers on tradedirectory.co.nz.
WorkSafe NZ also has guidance on working safely at height if you're using ladders for upper-storey brickwork.