How to clean mould moss and dirt off brickwork? (2026)
Quick Answer
To clean mould, moss and dirt off brickwork, start with the gentlest method: dry brushing, then washing with clean water and a mild cleaner suitable for masonry, following the product label. Work from the top down, avoid harsh pressure washing on older or damaged bricks, and stop if the brick face is crumbling, the mortar is loose, or the growth keeps coming back because that usually points to a damp or maintenance problem rather than a simple cleaning job.
Safety first
- Wear gloves and eye protection when brushing and whenever using cleaning products.
- Read and follow the cleaner manufacturer's safety instructions, including ventilation, contact precautions and disposal guidance.
- Never mix cleaning chemicals together, especially products containing bleach, ammonia or acids.
- Avoid high-pressure washing on unstable ladders or at height; do not attempt roof-edge or upper-storey work without safe access equipment and training.
- Protect plants, ponds, soil and surface water from run-off unless the product label confirms it is safe to do otherwise.
- Stop immediately if bricks crumble, faces flake off, mortar loosens, or water appears to be entering the building.
When to call a professional: Stop and consult a qualified professional if the brickwork is high up or needs unsafe access, if bricks are flaking or crumbling, if mortar joints are failing, if the wall is part of an older or historic building, if staining may be from salts or deeper damp rather than surface growth, or if regrowth is persistent despite cleaning and basic maintenance. If you are in New Zealand, you can find a verified, qualified local tradesperson through Trade Directory at tradedirectory.co.nz.
Overview
Brickwork usually gets dirty in layers: loose dust and soil on the surface, biological growth such as moss or algae where the wall stays damp, and darker mould staining where moisture and poor airflow persist. The safest approach is to remove the dry debris first, then clean in stages using the least aggressive method that works. That helps protect the outer fired face of the brick and the mortar joints, which can be damaged by wire brushing, strong chemicals or excessive water pressure. Before cleaning, check the condition of the wall. Sound, modern brickwork may tolerate more cleaning than soft, older, painted, frost-damaged or salt-contaminated brickwork. Also look for the reason the growth formed: leaking gutters, overflowing downpipes, blocked drainage, dense planting against the wall, failed pointing or roof run-off. If you clean without fixing the moisture source, staining and growth will often return. For light dirt, water and a soft or stiff non-metal brush may be enough. For biological growth, use a masonry-appropriate biocidal or fungicidal cleaner exactly as directed by the manufacturer, then rinse as instructed. Avoid mixing chemicals, avoid household bleach unless the product specifically states it is suitable for the surface and situation, and keep run-off away from plants and drains unless the label says disposal is safe.
Who this is for
Homeowners or occupiers cleaning accessible exterior brickwork with light to moderate dirt, moss, algae or mould staining, where the wall is otherwise in sound condition.
What you’ll need
- stiff non-metal brush
- bucket and clean water
- garden hose with gentle spray
- masonry-safe cleaner or biocidal wash suitable for brickwork
- gloves and eye protection
- old clothes and suitable footwear
- dust sheet or plastic sheeting to protect nearby plants and surfaces
- manufacturer instructions for any cleaning product used
Before you start
Inspect the brickwork closely in daylight. Do not start if bricks are flaking, powdering or cracked, if mortar joints are missing or loose, or if the area is high up and needs unsafe ladder work. Identify and, if possible, fix obvious moisture causes first, such as leaking gutters, overflowing downpipes, blocked drains, roof run-off, or vegetation trapping damp against the wall. Test any cleaner on a small inconspicuous area first, and check the product label for suitability, dwell time, rinsing instructions, surface compatibility and runoff precautions.
Step-by-step
- 1
Inspect the wall and deal with the moisture source
Look for blocked or leaking gutters, failed downpipes, splashing at ground level, damaged pointing, dense plants against the wall, or shaded areas that stay wet. Trim back vegetation and arrange repair of any defects before or soon after cleaning.
Why: Mould and moss usually return if the brick stays damp. Cleaning the wall without tackling the cause is only a short-term cosmetic fix.
- 2
Prepare the area and protect surroundings
Move outdoor furniture, cover nearby plants and vulnerable surfaces, and clear loose debris from the base of the wall. Put on gloves and eye protection, and keep children and pets away while you work and until the area is safe again.
Why: Cleaning products and dirty run-off can stain surfaces, irritate skin and eyes, and harm plants if not controlled.
- 3
Dry-brush off loose moss, dirt and debris
Using a stiff non-metal brush, brush the wall gently from top to bottom to remove loose growth, cobwebs and surface dirt. Collect and bag the debris rather than washing large clumps into drains.
Why: Removing dry material first reduces smearing, helps cleaner reach the staining underneath, and lowers the amount of contaminated run-off.
- 4
Pre-wet and test a small area
Lightly wet the brickwork with clean water if the cleaner instructions allow, then apply the chosen brick-safe cleaner or biocide to a small hidden section exactly as directed on the label. Check for discolouration, residue or surface damage before proceeding.
Why: A test patch helps confirm the product is compatible with the brick and mortar and reduces the risk of visible damage.
- 5
Clean in sections from the top down
Apply the cleaner to manageable areas, allow it to work for the time stated on the product instructions, then scrub gently with the brush. Rinse or leave as directed by the manufacturer, always working from the top of the wall down so dirty water does not streak already-cleaned areas.
Why: Section-by-section cleaning gives better control, prevents premature drying, and helps you avoid uneven results.
- 6
Rinse carefully and check the joints
Where rinsing is required, use a gentle hose spray rather than a concentrated jet. After cleaning, inspect the mortar joints and brick faces for loosening, pitting or fresh cracking.
Why: High force can erode mortar and the outer face of the brick. Post-cleaning inspection helps you catch hidden damage early.
- 7
Dry out the area and monitor regrowth
Let the wall dry naturally with good airflow. Over the next few weeks, watch for rapid regrowth, persistent dark patches or damp marks returning in the same places.
Why: Fast regrowth or recurring damp often indicates an underlying defect that needs repair rather than repeated cleaning.
Why this works
Dirt and biological growth on brickwork are usually surface-bound and easier to remove when tackled in layers: first the loose material, then the remaining staining with a masonry-safe cleaner. Gentle mechanical action and the correct cleaner lift contamination without unnecessarily damaging the brick face or mortar.
Common mistakes to avoid
- Using a pressure washer too aggressively, especially on old, soft or damaged brickwork
- Scrubbing with a wire brush, which can scar the brick face and damage mortar
- Applying strong chemicals without checking they are suitable for masonry
- Skipping a test patch on an inconspicuous area
- Cleaning the wall but ignoring leaking gutters, bad drainage or trapped moisture
- Mixing cleaning chemicals or decanting them into unlabelled containers
Troubleshooting
Green or black staining comes back quickly
Check for persistent damp, shade, blocked gutters, overflowing downpipes, failed pointing or vegetation holding moisture against the wall. Fix the moisture issue before repeating treatment.
White powder appears after cleaning
This may be efflorescence rather than dirt. Let the wall dry fully and brush it off dry; if it persists, investigate moisture movement through the wall rather than repeatedly washing it.
Brick surface starts flaking or powdering
Stop cleaning immediately. The brick face may be deteriorating or salt/frost damaged. Get the wall assessed before doing anything more.
Streaks remain after rinsing
Re-clean smaller sections from the top down, keeping the area evenly wet as required by the product instructions and avoiding dirty run-off drying on the surface.
Compare your options
Brush and water only
Best for: Light dust, loose dirt and very mild surface growth
Pros: Lowest risk to brickwork, inexpensive, simple
Cons: Often not enough for established mould, algae or moss staining
Masonry-safe biocidal or fungicidal cleaner
Best for: Moss, algae, mould and recurring biological staining on sound brickwork
Pros: More effective on living growth, can reduce regrowth when used properly
Cons: Needs careful handling, label compliance and protection of nearby plants and surfaces
Pressure washing
Best for: Limited use on robust modern masonry when appropriate and done carefully
Pros: Fast dirt removal over large areas
Cons: Higher risk of eroding mortar, driving water into the wall and damaging brick faces; often unsuitable for older or fragile brickwork
| Option | Best for | Pros | Cons |
|---|---|---|---|
| Brush and water only | Light dust, loose dirt and very mild surface growth | Lowest risk to brickwork, inexpensive, simple | Often not enough for established mould, algae or moss staining |
| Masonry-safe biocidal or fungicidal cleaner | Moss, algae, mould and recurring biological staining on sound brickwork | More effective on living growth, can reduce regrowth when used properly | Needs careful handling, label compliance and protection of nearby plants and surfaces |
| Pressure washing | Limited use on robust modern masonry when appropriate and done carefully | Fast dirt removal over large areas | Higher risk of eroding mortar, driving water into the wall and damaging brick faces; often unsuitable for older or fragile brickwork |
Alternatives
- Arrange a specialist masonry cleaning contractor if the staining is extensive, the brickwork is historic, or access is difficult
- Improve drainage, sun exposure and airflow first, then use only light brushing if the growth is minor
Pro tips
- Work on a cool, dry day rather than in strong sun, so the cleaner does not dry too quickly on the wall
- Use separate brushes for dry debris removal and wet cleaning
- Keep notes of the product used and the date, which helps if you need to assess regrowth later
- If the wall is near a roof edge, check whether roof run-off is dirtying the brickwork before blaming the wall itself
Legal & regulatory notes
Product use, runoff disposal and work at height may be subject to local environmental and health and safety rules. Follow the product label and any local council or environmental guidance, especially if wash water could enter stormwater drains or neighbouring property.
What this guide does not cover: This guide covers general cleaning of accessible exterior brickwork with surface mould, moss and dirt. It does not cover historic conservation cleaning methods, internal mould remediation, structural brick repairs, chemical stain removal for paint or graffiti, asbestos risks, or diagnosis of complex damp problems.
Cost considerations
Costs vary mainly with access, wall condition, the cleaner chosen and whether repairs to gutters, pointing or drainage are needed. Repeated cleaning is usually poorer value than fixing the damp source causing regrowth.
Prefer to hire a professional?
If this job is beyond a confident DIY — or the work needs to be done by a licensed professional — you can find a verified roofer through these directories of real, verified trade businesses. Compare local tradespeople, read their details and request quotes before you commit.
Frequently asked questions
Can I use bleach on brickwork?+
Only if the product is specifically suitable for masonry and you follow its label exactly. Some chemical cleaners can discolour brick, harm mortar, damage nearby plants or create hazardous fumes if mixed with other products.
Is pressure washing safe for brick walls?+
Sometimes, but it is often overused. It can remove surface dirt quickly, but it can also erode mortar joints, damage the fired face of bricks and drive water into the wall, especially on older or already damaged masonry.
Why does moss or mould keep coming back?+
Usually because the wall stays damp. Common causes are shade, poor airflow, leaking gutters or downpipes, rising splashback from ground level, blocked drainage, or vegetation holding moisture against the wall.
How do I know if the wall needs repair instead of cleaning?+
If bricks are crumbling, spalling, cracked, or powdery, or if mortar joints are missing or soft, stop cleaning and get the wall assessed. Those are repair issues, not just surface dirt.
What if the white marks are not dirt?+
They may be efflorescence, which is salt brought to the surface by moisture. Brushing it off dry after the wall has dried is usually safer than repeated washing, but persistent efflorescence means the moisture source needs investigating.
Sources & references
Guidance on this page is traced to documented sources. Last checked 25 September 2026.
- HSE - Working at height · government
Supports the safety advice not to attempt unsafe ladder or roof-edge work and to use proper access methods.
- Centers for Disease Control and Prevention - Mold Cleanup in Your Home · government
Supports general mould-cleaning safety such as protective equipment, cleaning precautions and avoiding unsafe exposure.
Basic cleaning principles stay fairly stable, but product instructions, environmental guidance and safety rules can change.