How to Clean Brickwork Without Taking the Face Off It (A London Guide)

If you're wondering how to clean brickwork without damaging it, start with the gentlest method that works: clean water, a soft nylon brush and a test patch somewhere nobody looks. Green growth gets killed with a surface-safe treatment at low pressure, not blasted off. What you don't do to old London brick is jet wash it.

This guide is for London homeowners and landlords looking at a green, black or patchy wall and weighing up a hired pressure washer, a bottle from the DIY shop or a phone call. It covers bare brick only. If your walls are rendered, our guide to cleaning render without wrecking it covers that side.

First, work out what's actually on the brick

Green, black and white marks are different problems, and the fix for one can make another worse. Spend two minutes looking before you spend a Saturday scrubbing.

Here's how to read your wall:

• Green film, furry moss or crusty patches, worst on the shaded side. Living growth: algae, moss or lichen. The brick maker Wienerberger notes in its advice on cleaning bricks that "moss, algae and lichens thrive in damp, cold, shaded areas". This is the one a gentle clean properly fixes.
• Black or dark grey, fairly even across the wall. On an older London house this is often old pollution in the surface of the brick. It gets its own section below.
• A white, powdery bloom. That's efflorescence, salts carried to the surface by moisture. Wienerberger calls it "generally a harmless and temporary effect that should weather away with time". Leave it, or brush it off with a soft brush once it's dry.
• Grey or white smears and crusts near newer work. Mortar splashes, or lime leaching from the joints. Once hardened, Wienerberger says lime staining "can only be removed by an acid solution", which is a different job entirely.
• Orange, brown or rusty patches. Iron compounds drawn to the surface by moisture. Wienerberger says iron and manganese stains "are best left to weather away naturally", and warns that hydrochloric acid cleaners can react with them and leave a permanent dark stain.

Only the green one is reliably a cleaning job. The rest are best left alone or belong to a different trade.

Is it okay to pressure wash bricks?

Not on old London brick, no. High pressure strips the face off the brick and digs out the pointing, and a jet wash is the quickest way we know to make a tired wall look worse.

London stock brick is soft and porous, and its outer face is the toughest part, the bit keeping the weather out. Put a pressure washer on it and the face comes off in stripes and patches, leaving a blotchy finish that looks worse than the algae did. The softer brick underneath soaks up water, and the shaded side stains green.

The pointing gets it too. A jet tracked along a joint pulls out soft old mortar, and every gap it leaves lets rain in.

This isn't a cleaner being precious. Historic England's research on biological growth on masonry says even conventional cleaning with water "causes some loss of the surface", and that "overzealous cleaning (for example, with high pressure jets) can cause roughening of the surface as well as significant damage". Wienerberger agrees that high pressure washing "is not recommended for brickwork", warning that it can leave brickwork "vulnerable to water penetration and frost attack".

What works instead is the approach we use on render: low-pressure soft washing for brick and render. A surface-safe treatment goes on at low pressure and kills algae, mould and green growth at the root, rather than forcing water behind the face of the brick.

Why London brick turns black, and when to leave it alone

Black brick on a Victorian terrace usually isn't last year's dirt. Quite often it's history.

When the Great Smog lifted on 9 December 1952, Historic England's blog on the smog describes a brisk wind "revealing greasy black-streaked streets, buildings and trees". The Clean Air Acts of 1956 and 1968 followed. On brick that old, some of the black can be that era's soot, still sitting in the surface.

In our experience that kind of black doesn't wash off. The methods strong enough to shift it are specialist chemical or abrasive cleaning, which can do real damage in the wrong hands. Anyone promising a "like new" finish on 120-year-old brick is either guessing or planning to use something harsh.

Historic England's research has a section headed "Cleaning may not always be the right answer", and it describes organic growth as part of "the natural, aged patina that gives masonry its appealing aesthetic on historic structures".

Our rule of thumb: if the colour is even and the brick and pointing are sound, leave it. Same if the house is listed or in a conservation area. An evenly weathered wall looks deliberate. A half-cleaned one, pale in stripes where someone got keen with a lance, looks like a mistake.

Not sure if it's soot or growth? In our experience a small test patch settles it: treated growth fades, old soot doesn't budge.

How to clean brickwork yourself, step by step

For a garden wall, a porch or the bottom metre of the house, a bucket and a brush will get you a long way. Go slowly, and stop the moment the brick looks worse.

One London catch first. Thames Water's hosepipe ban has been in force since 23 July 2026, and walls are on its list of things you must not clean with a hosepipe or pressure washer. Some business activities are exempt, but for your own DIY it's a bucket for now. Other water companies have their own rules, so check yours.

1. Pick a dry, mild day. Never in a frost: Wienerberger warns that in very cold conditions "the wet brickwork will freeze". Dry weather also stops any treatment getting diluted.
2. Protect what's below. Cover delicate plants, wet the rest down, and move anything you don't want splashed.
3. Brush off loose growth while it's dry. Use a soft or medium nylon brush, never a wire brush, which Wienerberger says "can damage the brick face".
4. Choose a test patch. Low down and out of sight, about the size of a sheet of A4. Round the side or behind the bins is ideal.
5. Wet it, then wash it. Dampen the patch with clean water, then work in a mild detergent solution with a nylon brush. Small circles, light hands.
6. Rinse from the top down with clean water and a sponge.
7. Use a masonry biocide on green growth, exactly as the label says. Give it time to work rather than scrubbing the brick raw.
8. Judge it dry, a few days later. Wet brick always looks darker. If the patch dries paler, blotchy or rough to the touch, stop there.

If the patch looks good, carry on in small sections. If it doesn't, you've ruined a bit of brick behind the bins, not the front of the house.

Where DIY stops, and the jobs that aren't cleaning at all

Once a job needs a ladder, an acid or a blaster, it isn't a weekend job any more.

Height. Anything above what you can reach from the ground needs proper access. A wet wall and a ladder is a bad combination.

Acid. Acid cleaners are how hardened lime crusts and mortar stains come off, and they're unforgiving. Wienerberger's warning about hydrochloric acid leaving a permanent dark stain tells you how easily it goes wrong.

Sand or grit blasting. It strips the face off the brick, and it makes dust. HSE's guidance on lung disease lists blasting among the tasks that can produce silica-containing dust from materials including brick, and says long-term exposure can lead to silicosis. Not one to hire a machine for.

Crumbling pointing. Cleaning won't fix it, and a jet wash will finish it off. That's a job for a bricklayer who knows old brick.

We don't do acid cleaning, blasting, repointing or graffiti removal. They're different trades, and we'd rather say so than pretend otherwise. Our end of the job is the gentle end: low pressure and a treatment that kills the growth.

Listed building or conservation area? Check before anyone touches it

This is the one that can turn a cleaning job into a legal problem.

Listed building consent isn't only for extensions. The Planning Portal's guide to listed building consent says the controls apply to works that alter a listed building in a way "which is likely to affect its character as a building of special architectural or historical interest". It also says "it is a criminal offence to carry out work which needs listed building consent without obtaining it beforehand".

Cleaning isn't automatically in or out of that. But a clean that changes the colour or surface of a listed brick front is the sort of thing a council could decide affects its character, and that's their call, not yours or your cleaner's.

Before anyone starts:

• Search your address on the National Heritage List for England, Historic England's official register of protected buildings.
• Check your council's website for conservation areas, or ask the planning team.
• If the house is listed, speak to the council's conservation officer before you book anybody.

Specialist conservation cleaning of listed buildings isn't something we take on. If your house is listed, you want someone the conservation officer is happy with, and we'll tell you that rather than quote for it.

How long does clean brickwork stay clean?

A good two to three years, typically, after a proper treatment. Sun and airflow decide where in that range you land, and a north-facing wall under trees goes green again faster than an open, sunny front.

Historic England's research also reports "an observed increase in 'greening'" on masonry, which it links to changes in climate, particularly temperature and rainfall. If your wall greens up quicker than it used to, that may be part of the reason.

Mostly, though, regrowth comes down to water. An overflowing gutter tips rain down the same strip of brick every time it pours, and that strip usually goes green first. A leaking downpipe joint does the same. Wienerberger makes the point that if damp, shaded conditions "can be addressed, the organic matter will usually reduce without a chemical treatment". So getting the gutters cleared before the walls are done is money well spent.

It's also why most people book the whole outside of the house in one go: walls, fascias and soffits together. Gutters and fascias first, walls next, glass last, so nothing clean gets dirty water run down it.

When it isn't worth paying anyone

We'd rather you kept your money than spent it on a wall that doesn't need us. Save it if:

• It's white bloom on a fairly new wall. That's efflorescence, and it usually weathers away on its own.
• The brick is evenly dark and sound, with decent pointing. That's age, not dirt.
• It's a low garden wall or the bottom few courses of brick. The steps above will get you there.
• A gutter is pouring down the wall. Fix that first, or you'll pay to clean the same stripe twice.
• The house is listed. Talk to the council before you talk to any cleaner.

Where it is worth paying: whole elevations above ladder height, heavy green growth on a shaded side, or a front you'd rather not gamble on with a hired machine.

FAQ

What is the best thing to clean bricks with? Clean water and a soft nylon brush, with a mild detergent if it needs a bit more. For green growth, a masonry biocide used exactly as the label says. Never a wire brush, which can damage the face of the brick.

How do you make brickwork look new? On old brick you usually can't, and it's better not to try. Cleaning removes growth and grime, but the weathered colour of century-old brick is part of the brick. Methods that make it look new tend to do it by stripping the face, which leaves it patchy and more open to damp.

How do you clean bricks that have turned black? Work out what the black is first. Growth on a damp, shaded wall responds to a low-pressure treatment. Decades-old soot on a London stock brick front usually won't wash off, and the methods that do shift it are specialist work, so leaving it is often the better call.

How do you get rid of green algae on brick walls? Kill it rather than blast it. A treatment applied at low pressure kills the growth at the root without forcing water behind the face of the brick. Fix whatever keeps the wall wet, like an overflowing gutter, and a proper treatment typically lasts two to three years.

Are white marks on brick a problem? Usually not. White, powdery marks are efflorescence, salts carried to the surface by moisture, and Wienerberger describes it as generally harmless and temporary. Brush it off when dry or let the weather take it.

Do I need permission to clean a listed building? You might. Listed building consent is needed for works likely to affect a listed building's character, and doing that work without consent is a criminal offence. Whether a particular clean counts is the council's call, so ask their conservation officer before anyone starts.

Getting a straight answer on your wall

Send us a photo of the worst side of the house and we'll tell you what's on it. If it's green growth on brick or render, that's what our render and brick soft washing is for, and you'll get a free, fixed quote before any work starts. If it's old soot, salts or tired pointing, we'll say so and save you the money.

Get a free, no-obligation quote, call us on 07375 104665, or message us on WhatsApp at wa.me/447375104665 for a same-day answer. We cover North London and the Hertfordshire borders.

Last updated: 11 September 2026

About Techno Clean: a London deep-cleaning company covering North London and the Hertfordshire borders. We specialise in one-off deep cleans, end of tenancy and after builders cleaning, fully insured with £5 million public liability cover and DBS-checked teams, rated 4.9 from over 180 reviews across 500+ completed jobs.