How do i clean mould moss and dirt off brickwork? (2026)
Quick Answer
Clean brickwork by starting with the gentlest method: dry brushing, then washing with clean water and a mild detergent if needed, and only using a suitable biocide or brick-safe cleaner for persistent moss, mould or algae growth. Avoid harsh pressure washing and strong acids unless the brick manufacturer or a conservation professional says they are suitable, because they can damage the brick face, mortar joints and nearby materials.
Safety first
- Do not work at height without proper equipment and training; cleaning near eaves, gutters or upper brickwork is often safer for a professional.
- Wear gloves and eye protection, especially when brushing overhead or using any cleaning product.
- Never mix bleach, acids, ammonia-based cleaners or other chemicals; dangerous gases or reactions can occur.
- Use only products labelled as suitable for the surface and follow the manufacturer instructions exactly.
- Protect plants, ponds, metal fixtures and painted surfaces from overspray and runoff.
- Avoid directing water into vents, weep holes, cracks, roof edges or open joints where it can enter the building fabric.
- Stop immediately if brick faces, pointing or render begin to crumble, flake or detach.
When to call a professional: Stop and consult a qualified professional if the brickwork is high or hard to reach, the wall is old, listed or fragile, mortar joints are loose or crumbling, the brick face is flaking, staining keeps returning, or you suspect a roof leak, gutter defect or penetrating damp is keeping the wall wet. If you are in New Zealand and need help with access, roof drainage, masonry repairs or damp diagnosis, you can find a verified qualified local tradesperson through Trade Directory at tradedirectory.co.nz.
Overview
Mould, moss and general dirt on brickwork are often caused by a mix of moisture, shade, poor drainage and surface contamination. The safest approach is to remove loose growth first, clean with the least aggressive method that works, then deal with the reason the wall stays damp so the problem does not come back quickly. For most modern external brickwork, that means brushing off loose material, wetting the area, gently scrubbing with water and a mild cleaning solution, rinsing well, and using a product specifically labelled for biological growth only if staining or regrowth remains. Take extra care with older, soft, painted, rendered, sealed or damaged brickwork. These surfaces can be harmed by hard scrubbing, bleach misuse, high-pressure washing or acidic cleaners. Mortar joints are often more vulnerable than the bricks themselves, so inspect them before you start. If the wall is high up, hard to access, heavily stained, crumbling, or the growth is widespread and linked to a roofing leak, overflowing gutter or penetrating damp, cleaning alone will not solve it. In those cases, it is safer and more effective to fix the moisture source first and get professional help if needed.
Who this is for
Homeowners or occupiers cleaning accessible external brickwork at low level, where the wall is structurally sound and the contamination is light to moderate.
What you’ll need
- stiff but non-metal brush
- bucket
- clean water
- mild detergent suitable for exterior surfaces
- garden hose or low-pressure rinse
- PPE such as gloves and eye protection
- plastic sheeting or a way to protect nearby plants and surfaces
- a brick-safe biocide or exterior cleaner if simple washing is not enough
Before you start
Check whether the brickwork is sound, whether mortar joints are loose or crumbling, and whether there is an obvious moisture source such as leaking gutters, roof run-off, failed pointing, blocked drainage or heavy shade. Read the product label for any cleaner you plan to use, test it on a small hidden area first, and avoid cleaning in very hot sun or when rain is imminent.
Step-by-step
- 1
Inspect the wall and find the moisture source
Look for leaking gutters, downpipes discharging onto the wall, cracked pointing, overflowing roof edges, poor ground drainage, dense vegetation against the wall, or areas that stay shaded and damp. Check whether the contamination is just on the surface or whether the brick or mortar is flaking, soft or cracked.
Why: Moss and mould return quickly if the wall remains damp, and visible damage can mean the surface is too fragile for DIY cleaning.
- 2
Prepare the area and protect surroundings
Move items away from the wall, cover delicate plants and nearby finishes, and wear gloves and eye protection. If you are using a proprietary cleaner, follow the label exactly for handling, application and rinsing. Keep children and pets away until the area is safe again.
Why: Cleaning runoff can affect plants, metals, painted surfaces and skin or eyes.
- 3
Remove loose growth dry first
Brush off loose moss, cobwebs, flaky dirt and surface debris with a stiff non-metal brush, working from top to bottom. Collect the debris rather than washing large clumps straight into drains.
Why: Dry removal reduces smearing, uses less water and lets you see what staining remains after the biological growth is gone.
- 4
Pre-wet the brickwork
Lightly wet the wall with clean water before using any detergent or cleaner. Keep the surface damp rather than saturated.
Why: Pre-wetting helps prevent the brick and mortar from absorbing cleaning chemicals too quickly and makes scrubbing gentler.
- 5
Wash with the gentlest effective method
Scrub the area with water and a mild detergent using the brush, working in manageable sections from the bottom upward to reduce streaking, then rinse with clean water from top down. Use low pressure only.
Why: Most dirt and some light biological staining can be removed without aggressive chemicals or force, which lowers the risk of damaging the brick face and mortar.
- 6
Treat persistent mould, algae or moss staining if needed
If staining or regrowth remains, use a brick-safe exterior biocide or cleaner specifically intended for mould, algae or moss, and apply it exactly as the manufacturer directs. Test a small inconspicuous patch first, avoid mixing products, and rinse or leave to act only as directed on the label.
Why: Biological growth often roots into pores and joints, so a suitable treatment can kill residual spores better than detergent alone, but misuse can stain or damage masonry.
- 7
Rinse thoroughly and let the wall dry
Rinse away residues if the product requires rinsing, then allow the wall to dry naturally. Check the result once fully dry, because some staining looks worse while wet and some marks only show after drying.
Why: A proper final check helps you judge whether another gentle clean is needed or whether the remaining mark is permanent staining or damage rather than dirt.
- 8
Reduce regrowth
Trim vegetation back from the wall, clear gutters, improve drainage, and consider whether nearby roof run-off is wetting the brickwork. Repair any defects such as failed pointing or leaking gutter joints before the next wet season.
Why: Cleaning is only part of the job; controlling moisture is what keeps brickwork cleaner for longer.
Why this works
Mould, moss and algae thrive where masonry stays damp and dirty. Gentle physical removal lifts surface contamination, water and mild detergent remove general grime, and a suitable biocidal treatment can deal with lingering biological growth. Preventing repeated wetting is what slows recurrence.
Common mistakes to avoid
- Using high-pressure washing close to the wall, which can erode mortar, drive water into the wall and damage the brick face
- Using acidic or strong chemical cleaners without checking that they are suitable for the specific brick and mortar
- Cleaning before fixing leaking gutters, downpipes or drainage problems
- Scrubbing with metal brushes that can mark brick or leave rust stains
- Skipping a test patch on older, soft, painted or previously sealed brickwork
- Mixing cleaning chemicals or reusing unlabelled containers
Troubleshooting
Green or black staining comes back quickly
Look for an ongoing moisture source such as overflowing gutters, roof splash, blocked drainage, heavy shade or vegetation against the wall. Clean again only after the dampness issue is addressed.
White powder appears after cleaning
This may be efflorescence rather than dirt or mould. Let the wall dry fully and brush it off dry first; if it keeps returning, investigate moisture movement through the wall.
Brick surface starts flaking or mortar loosens
Stop cleaning. The masonry may be weathered, salt-damaged or too soft for DIY cleaning and should be assessed by a qualified professional.
Streaks remain after washing
Re-wet and clean in smaller sections, working consistently and rinsing thoroughly. Avoid letting cleaner dry on the wall.
Compare your options
Dry brushing and water only
Best for: Light dirt, loose moss and routine maintenance on sound brickwork
Pros: Lowest risk to brick and mortar, inexpensive, simple
Cons: May not remove embedded staining or kill spores
Mild detergent wash
Best for: General grime and light biological growth
Pros: Gentle, widely suitable, good first wet-cleaning step
Cons: May need repeat cleaning and may not stop regrowth on its own
Brick-safe biocide or specialist masonry cleaner
Best for: Persistent mould, algae or moss staining after basic cleaning
Pros: More effective on biological contamination, can slow regrowth
Cons: Requires careful label compliance, may affect nearby plants or finishes
Professional masonry cleaning
Best for: High walls, fragile brickwork, heavy staining, historic masonry, or moisture-related recurrence
Pros: Better diagnosis, safer access, lower risk of damage, can pair cleaning with repairs
Cons: Higher cost and may require specialist scheduling
| Option | Best for | Pros | Cons |
|---|---|---|---|
| Dry brushing and water only | Light dirt, loose moss and routine maintenance on sound brickwork | Lowest risk to brick and mortar, inexpensive, simple | May not remove embedded staining or kill spores |
| Mild detergent wash | General grime and light biological growth | Gentle, widely suitable, good first wet-cleaning step | May need repeat cleaning and may not stop regrowth on its own |
| Brick-safe biocide or specialist masonry cleaner | Persistent mould, algae or moss staining after basic cleaning | More effective on biological contamination, can slow regrowth | Requires careful label compliance, may affect nearby plants or finishes |
| Professional masonry cleaning | High walls, fragile brickwork, heavy staining, historic masonry, or moisture-related recurrence | Better diagnosis, safer access, lower risk of damage, can pair cleaning with repairs | Higher cost and may require specialist scheduling |
Alternatives
- For delicate or historic brickwork, ask a conservation or masonry professional about a suitable low-impact cleaning method instead of DIY scrubbing or chemical use.
- If the issue is mostly from shade and damp rather than ingrained dirt, improving drainage and sunlight exposure may reduce the need for repeated cleaning.
Pro tips
- Always start with the least aggressive method and only step up if needed.
- Take a photo before cleaning so you can compare results after the wall dries.
- If you are treating just one patch, clean a slightly larger area around it so the finish looks even.
- Keep soil, mulch and paving levels from bridging damp against the base of the wall where possible.
Legal & regulatory notes
Follow the product label and local council or environmental rules for chemical use and disposal of wash water, especially if runoff could enter stormwater drains or watercourses. If the building is listed, protected, or subject to heritage controls, cleaning methods may need specialist approval or conservation advice.
What this guide does not cover: This guide covers general cleaning of accessible external brickwork only. It does not provide project-specific chemical instructions, heritage conservation advice, safe access methods for working at height, diagnosis of structural movement, or a full damp-investigation process.
Cost considerations
DIY cleaning is usually low-cost if the wall is accessible and only needs brushing, water and mild cleaner. Costs rise if you need specialist biological treatments, access equipment, repointing, gutter repairs, or professional cleaning because the wall is high, fragile or repeatedly affected by damp.
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 a pressure washer on brickwork?+
Use caution. High pressure can damage mortar joints, remove the fired surface of some bricks and force water into the wall. If you use water at all, keep it low pressure and stop if any damage appears.
Will bleach clean mould off brick?+
Some cleaners contain bleach-based ingredients, but not all brickwork or nearby materials tolerate them well. Only use a product if the label says it is suitable for the surface, and never mix it with other cleaners.
Why does moss keep growing on the same wall?+
Usually because the area stays damp and shaded, or because roof or drainage defects keep wetting the brickwork. Cleaning helps, but you need to reduce the moisture source to slow regrowth.
Can I clean old or soft brick the same way as modern brick?+
No. Older, handmade or weathered bricks and lime mortar can be much more delicate. Use a very gentle approach and get specialist advice if you are unsure.
How do I know if it is dirt, mould or efflorescence?+
Dirt usually washes or brushes away, mould or algae often appears green, black or slimy in damp areas, and efflorescence is typically a white, powdery salt deposit that is often best brushed off dry once the wall has dried.
Sources & references
Guidance on this page is traced to documented sources. Last checked 25 September 2026.
- Health and Safety Executive - Working at height · government
Supports the safety advice to avoid unsafe work at height and to use proper precautions or professional help for elevated areas.
The basic cleaning approach changes slowly, but product-specific instructions and local environmental rules can change and should always be checked.