How to Clean Brick Efflorescence and Staining (Without Damaging Your Brickwork) – DIY Refurb

How to Clean Brick Efflorescence and Brick Salts on Exterior Walls (and Remove Ugly Stains for Good)

White, powdery patches on brickwork – often called brick salts – and random stains that won’t wash off are a very common headache for homeowners, landlords and anyone working on refurb projects. The good news is that, in most cases, brick efflorescence and staining are just cosmetic and can be cleaned – as long as you use the right method for the type of stain.

This guide walks you through what brick salts (efflorescence) actually are, how to safely remove them from brick, how to tackle other common stains, and what you can do to reduce the chance of it all coming back.

What Are Brick Salts / Brick Efflorescence?

Efflorescence – sometimes referred to as brick salts or salt staining – is the white, dusty or crystalline deposit you see on brick, block and mortar. It’s made up of soluble salts that have been carried to the surface by moisture. As the water evaporates, the salts are left behind as a white bloom.

These salts can come from:

The brick or block itself
The mortar or render
Adjacent materials (concrete slabs, coping stones, soil, etc.)

Efflorescence is usually most noticeable on newer brickwork or after periods of heavy rain and damp conditions. On its own it’s mainly an aesthetic issue, but because it’s driven by moisture movement, it can be a useful clue that water is getting into the wall more than it should.

Is Efflorescence a Serious Problem?

In many cases, efflorescence is a temporary cosmetic issue. Once the wall dries out and the bulk of the salts have been drawn out and washed away, it will often fade on its own.

However, it can point to underlying problems such as:

Poor detailing (copings, flashings, or cills not shedding water correctly)
Leaking gutters or downpipes soaking the wall
High external ground levels bridging the damp proof course
Persistent internal moisture, condensation or leaks

So while the white staining itself is not usually dangerous, it’s worth treating as both a cleaning job and a moisture investigation. Clean the surface, but also ask why the wall is staying damp enough for salts to keep appearing.

Before You Start: Safety and Preparation

Efflorescence and many brick stains can be treated with relatively mild methods, but you still need to protect yourself and the surrounding area. Before you begin:

Wear appropriate PPE: gloves, eye protection, and old clothing. If using any chemical cleaner, add a suitable mask and follow the manufacturer’s safety instructions.
Protect nearby surfaces: mask off or sheet timber, metal, glass, painted areas and plants that could be affected by splashes or run-off.
Check the brick type: some soft, historic or handmade bricks are more vulnerable to damage from aggressive brushing or strong acids. If in doubt, always test on a small, hidden area first.
Work on a dry day if possible: this makes it easier to see what’s going on and helps the wall dry out properly afterwards.

Step 1: Identify the Type of Stain

Not all “white marks” or discolorations on brick are efflorescence. Identifying the stain will help you choose the right cleaning method:

Efflorescence / brick salts: fine, chalky or dusty white deposit that brushes off fairly easily when dry. Often patchy and spread over an area.
Lime staining / lime runs: harder, sometimes thicker white deposits or streaks, often beneath joints, copings or leaks. These can be tougher than normal efflorescence.
Green/black growth: algae, moss or lichen – usually in damp, shaded areas. Feels slimy or “green” rather than powdery.
Brown/orange stains: may be rust leaching from metal fixings or run-off from certain stone or concrete elements.
Dark grey/black patches around flues or chimneys: usually soot or smoke staining.

If you’re confident it’s efflorescence, start with the least aggressive cleaning methods below. For other stain types, skip ahead to the dedicated section for those stains.

How to Clean Efflorescence (Brick Salts) from Brick

The golden rule with brick cleaning is: start as gently as possible, and only step up to stronger methods if needed. Over-aggressive cleaning can permanently scar or erode the brick and mortar.

Step 1: Dry Brushing

Begin with a simple mechanical clean:

Wait for a dry spell so that the wall surface is as dry as possible.
Use a stiff plastic or natural-fibre brush (avoid wire brushes, especially on soft or decorative brick).
Brush the efflorescence off the surface, working downwards so you’re not dragging dust over cleaned areas.
Collect the dust with a vacuum or dustpan rather than washing it straight down onto paving or lower brickwork, where it can re-deposit.

Often, especially on newer walls, this basic brushing repeated a few times over several weeks is enough. Efflorescence tends to reduce naturally as the salts are removed and the wall dries out.

Step 2: Low-Pressure Rinse

If brushing alone doesn’t fully clear the deposits, you can move on to a controlled rinse:

Use a low-pressure hose or a pressure washer on its gentlest, widest fan setting held well back from the wall.
Work from the top down, allowing water to flow freely off the wall.
Avoid blasting directly into mortar joints, weep holes, vents or cracks.

The aim is simply to wash off residue – not to strip the surface of the brick. High-pressure washing can drive water deeper into the wall, damage mortar, and cause long-term issues.

Step 3: Mild Acidic Cleaner (If Needed)

Persistent or heavier efflorescence can sometimes require a proprietary brick cleaner or mild acidic solution designed for masonry. These products help dissolve the salts so they can be rinsed away more effectively.

If you decide to use a brick cleaner:

Choose a product specifically labelled as suitable for brick and efflorescence or brick salts.
Read all manufacturer instructions carefully before you start.
Pre-wet the brick with clean water so the cleaner doesn’t soak in too deeply.
Apply the cleaner in a small test area first, following the recommended dilution.
Allow the cleaner to dwell for the specified time, then agitate gently with a soft brush.
Rinse very thoroughly with clean water to remove all residues.

Safety note: never mix acidic cleaners with bleach or any chlorine-containing product – this can release dangerous gases. Always work in well-ventilated areas and wear full PPE.

Step 4: Repeat and Allow to Dry

Efflorescence can be stubborn. You may need to repeat the process a couple of times, especially on newer buildings or walls that have been saturated for some time. Allow the wall to dry out fully between treatments so you can see what has actually been removed and what is reappearing.

How to Clean Other Common Brick Stains

Many walls suffer from a combination of efflorescence and other stains. Here’s how to approach the most common ones.

Algae, Moss and Green/Black Growth

On north-facing walls, shaded areas, and around leaky gutters or downpipes, you’ll often see green or black organic growth on the brick surface.

To treat it:

Brush off as much loose growth as possible with a stiff brush.
Apply a suitable exterior biocidal wash or moss & algae cleaner following the manufacturer’s instructions.
Allow the product to dwell for the recommended time so it can kill spores, not just surface growth.
Rinse or leave as directed; some products are designed to work gradually with weathering.

To reduce regrowth, deal with underlying moisture – fix leaks, improve drainage, and try to improve airflow where possible.

Rust Stains

Brown or orange streaks running down brickwork often indicate rusting from metal fixings, railings, brackets, or sometimes certain stones or concrete elements with iron content.

To remove rust staining:

Identify and address the source of the rust first – treat or replace rusting metal, add protection, or improve detailing so water doesn’t constantly run over the same spot.
Use a proprietary rust remover suitable for masonry (often based on oxalic acid or similar). Always test in a small, hidden area first.
Apply as directed, gently agitate if required, then thoroughly rinse away.

Some deep rust staining can be very stubborn and may not disappear entirely without professional cleaning or more specialist techniques.

Soot, Smoke and Pollution Staining

Brick around chimneys, flues and busy roads often picks up dark grey or black staining that doesn’t brush off easily.

For these stains:

Start with a good dry brush to remove any loose dirt.
Use a neutral or mildly alkaline masonry cleaner designed for soot and carbon deposits (rather than an acid cleaner).
Apply according to instructions, work it into the surface with a soft brush, then rinse thoroughly.

If staining is very heavy or historic, a professional cleaning contractor with access to low-pressure, specialist systems may be the safest option to avoid damaging older brickwork.

Paint, Mortar and Construction Splashes

On refurb and new-build jobs, it’s common to find paint drips, mortar smears or other construction marks on brick.

General approach:

For fresh splashes, remove them as quickly as possible with water and a sponge before they cure.
For cured mortar smears, use a specialist mortar or cement remover suitable for brick – not just generic strong acid. Test first and follow instructions carefully.
For paint, a masonry-safe paint remover or poultice-type stripper may be needed. Avoid aggressive scraping that can gouge the brickface.

How to Reduce the Chances of Efflorescence and Staining Returning

Cleaning brick is only half the story. To keep walls looking better for longer, aim to control moisture and improve detailing so water doesn’t constantly move through the masonry.

Find and Fix Moisture Sources

After cleaning, inspect the building with an eye for where water is coming from:

Gutters and downpipes: repair leaks, clear blockages and ensure water is discharged away from the wall.
Copings, cills and flashings: check that they project and drip correctly, and that sealants or flashings are in good condition.
Ground levels: make sure soil, paving or decking isn’t bridging the damp proof course. Ideally, external ground should finish at least 150mm below the DPC.
Pointing and cracks: repoint any failed mortar joints with a compatible mortar and repair significant cracks to reduce direct water ingress.
Internal sources: resolve leaks from plumbing, and improve ventilation in kitchens, bathrooms and basements to reduce internal moisture passing through the wall.

Consider a Breathable Protective Treatment

In some cases, once the wall is fully cleaned and dry, applying a breathable masonry water-repellent can help reduce rain penetration while still allowing trapped moisture to escape. This can limit the amount of water that travels through the brick and carries salts to the surface.

The key is to choose products that remain vapour-permeable and are specifically designed for brick and mortar, rather than non-breathable coatings that can trap moisture behind the surface.

When to Call in a Professional

Many light efflorescence and staining issues are well within the capabilities of a careful DIYer. However, it’s worth bringing in a specialist if:

The building is listed, historic, or uses very soft or decorative brick.
Efflorescence is severe and keeps returning despite your efforts.
There are signs of deeper damp problems, such as crumbling plaster, mould or damp patches internally.
You’re unsure which cleaners or techniques are safe for your particular brickwork.

A professional can assess the moisture routes, recommend appropriate remedial work, and use controlled cleaning methods and equipment to protect the brick surface.

FAQs

What are brick salts?

“Brick salts” is a common name for efflorescence – the white, powdery deposits that appear on brickwork when moisture carries soluble salts to the surface. They look unsightly but are usually a cosmetic issue and can be cleaned off with the right method.

Will brick salts damage my wall?

On their own, brick salts are mostly cosmetic. However, they are a sign that moisture is moving through the wall, so it’s important to check for leaks, high ground levels or other damp issues and sort those as well as cleaning the surface.

Can I paint over efflorescence?

Painting over active efflorescence is not recommended. The salts and moisture will usually push through the paint, causing blistering or peeling. Clean the brick, tackle the moisture source, and allow the wall to dry thoroughly before considering any breathable paint or coating.

Summary

Efflorescence and staining on brickwork can look worrying, but in most cases they are manageable with the right approach:

Identify the type of staining you’re dealing with – brick salts, algae, rust, soot, or construction marks.
Start with gentle methods: dry brushing and low-pressure rinsing.
Use suitable masonry cleaners carefully where necessary, always testing a small area first.
Address the underlying moisture sources to prevent the problem recurring.

By combining sensible cleaning with good moisture control and detailing, you can restore tired brickwork and keep it looking clean and solid for years to come.