What Is Soft Washing? How It Works and When Your Walls Need It

Soft washing is a way of cleaning exterior walls, roofs and cladding with low water pressure and a specialist biocide solution. Instead of blasting algae, lichen and mould off the surface, the solution soaks in and kills the growth at the root. A gentle rinse then takes the dead material away, and the wall carries on brightening for days afterwards.

If you've got a render wall going green on the north side, black streaks down the cladding, or a managing agent sending you photos of a block that looks tired, this is probably the method you've been quoted for. Here's what it actually involves, and how to tell the real thing from a man with a jet washer who's learned a new word.

What soft washing actually is

Soft washing is a chemical process, not a pressure process. That's the whole idea.

A biocide solution, usually a diluted sodium hypochlorite or a DDAC-based biocide with a surfactant to help it cling, goes on at low pressure. No more force than a garden sprayer. It's left to dwell, typically ten to thirty minutes depending on the surface and how bad the growth is, so it can work down into the pores of the wall and kill the spores you can't see as well as the green you can.

Then it's rinsed gently, and in a lot of cases the surface keeps improving over the following week as the dead growth weathers off. Lichen is the slow one. The black and white crusty patches die in the treatment but can take weeks to release their grip, and that's normal, not a failed job.

You'll also hear it called softwashing, low-pressure cleaning or a biocide treatment. Same thing.

Soft wash vs pressure wash: the honest comparison

Neither method is "better". They're different tools, and the damage happens when the wrong one gets used on the wrong surface.

• The force. A pressure washer runs anywhere from 100 to 250 bar. A soft wash application is closer to a garden hose. One strips, the other soaks.
• What each one removes. Pressure washing shears off whatever is on the surface, and leaves the spores sitting in the pores underneath. Soft washing kills the organism itself, root and spore.
• On render. Modern thin-coat render is measured in millimetres. High pressure takes the textured face off, and patches never match again. Soft washing leaves the surface untouched.
• On painted surfaces. A jet finds every weak edge in a paint film and lifts it. Once paint starts peeling, you're repainting the whole elevation, not just the corner.
• On pointing. A focused jet erodes mortar out of the joints, especially older lime pointing. Repointing a wall costs many times what cleaning it does.
• How long the result lasts. A pressure-washed wall often greens up again within a season, because the growth was never killed. A soft-washed wall stays clean for years, because it was.

Pressure washing is still the right tool for hard ground surfaces that can take it. Block paving, concrete drives, stone patios. We run both, and we pick per surface, not per van load.

What soft washing cleans

Most exterior surfaces that go green, black or streaky are candidates.

• Render. The big one. K Rend, monocouche, acrylic and silicone thin coats, plus older sand and cement and even pebbledash. Our guide to cleaning render without wrecking it goes deeper on the different systems and why a lance should stay away from all of them.
• Cladding. Powder-coated panels, aluminium, steel and uPVC cladding on houses, shopfronts and commercial blocks. Algae sits in the panel joints and around fixings where a jet just forces water inside. For larger commercial panel work, see our cladding cleaning service.
• Brick and stone. Brick responds well, though soot and carbon staining sometimes needs a detergent stage first. Soft natural stone, like some sandstones, wants extra care with dilution. Our brickwork cleaning guide covers the differences.
• Fascias, soffits and uPVC. The green film on white fascias is usually algae feeding on gutter overspill. Soft washing takes it off without forcing water into the roofline vents. And if the gutter above is the cause, it's worth having the gutters and downpipes cleared at the same visit, or the stripe comes back.
• Roofs. Moss and lichen on tiles are soft-wash territory too, either scraped then treated or treated from the ground. Walking a roof with a pressure lance is how tiles crack and lofts get wet.

The chemicals, and the rules around them

"Soft washing chemicals" sounds alarming. It shouldn't, but it does deserve a straight answer, because this is the part of the job where corners get cut.

The active ingredients in the trade are sodium hypochlorite, essentially a strong, professional-grade bleach, and DDAC biocides. Both are regulated products in the UK. Under the GB Biocidal Products Regulation, biocides supplied in Great Britain must be authorised, and HSE publishes a list of authorised products with expiry dates for supply and use.

Why that matters to you: a proper contractor can tell you exactly which product is going on your wall and at what dilution. If someone can't name it, or mumbles something about a secret mix, that's a problem. It might be an unauthorised product, or a homemade brew at a strength that scorches your planting and does nothing for the spores.

Protecting plants, ponds and drains

This is the part DIY attempts, and cheap quotes, usually get wrong.

Before anything goes on the wall, planting gets soaked with clean water so it can't take up the solution, and anything delicate gets sheeted. Fish ponds get covered. After the rinse, everything gets watered down again.

Runoff is the other half of it. The government's pollution prevention guidance for businesses is blunt: "You must not let your business or organisation cause or allow pollution", and it points out that surface water drains discharge directly to the environment, so even detergents can pollute. In practice that means wash water shouldn't be hosed towards a road gully. We control where the runoff goes, keep volumes low, and rinse surfaces so residue is heavily diluted by the time it reaches soil.

Your hedge should look exactly the same the day after as it did the day before. That's the standard.

How long does soft washing last?

On render, with a proper biocide treatment, about two to three years before it needs doing again.

What shifts it within that range is the wall itself. North-facing elevations, walls under trees, and anywhere a leaking gutter keeps things wet will go first. A sunny south-facing wall can stay visibly clean well past the point its shaded twin needs retreating.

Compare that with pressure washing alone, which can look green again within a single season. The surface was scraped clean but the spores were left alive in the pores, and algae doesn't need much encouragement in a British autumn.

How to spot a "soft wash" that isn't

Soft washing has become a selling phrase, and not everyone using it means it. And when it goes wrong, the repair bill is always bigger than the clean would have been.

The tells:

• Only a pressure washer on the van. A genuine soft wash needs a tank, a pump or sprayer, and the chemicals. If the only kit is a petrol jet washer, you're getting a jet wash whatever the quote says.
• Can't name the product. Ask what's being applied and at what dilution. A real answer names an authorised biocide. A vague answer is your cue to end the conversation.
• No mention of dwell time. If the plan is spray and immediately rinse, nothing is being killed at the root. The chemistry needs its minutes.
• No plant or drain protection. No pre-wetting, no sheeting, no thought about runoff means the "saving" is being made on the slow, careful part of the job.
• A turbo nozzle near render. If you see a spinning pencil jet going anywhere near a rendered or painted wall, stop the work.

None of this needs you to be an expert. Two questions do it: what product are you using, and how long does it dwell?

When soft washing is the wrong tool

Honest list, because sometimes we're not what you need:

• Oil, grease and chewing gum. Those need degreasers, heat or steam, not a biocide. Biology isn't the problem.
• Paint splashes, graffiti and cement residue. Different chemistry again, often solvent-based or mechanical.
• Rust and metallic staining. Needs a specialist rust remover, and we'd rather tell you that upfront.
• Blown or crumbling render. If the render has lost its bond or is coming away, cleaning is the last thing it needs. That's a renderer's job first, and no honest cleaner will spray it.
• Freshly painted walls. Coatings need time to cure. A biocide on new paint can mark it, so we wait.

If we're not the right tool, we'll say so on the phone. It saves everyone a wasted visit.

FAQ

Is soft washing better than pressure washing? For walls, render, cladding and roofs, yes, because it kills the growth rather than stripping the surface. For hard ground like block paving and concrete, pressure washing is usually the right tool. Most exterior jobs use each where it belongs.

What chemicals are used in soft washing? Typically a diluted sodium hypochlorite solution or a DDAC-based biocide, with a surfactant to help it cling. In Great Britain these are regulated under the GB Biocidal Products Regulation, and your contractor should be able to name the authorised product they're using. You can check any product against HSE's list of UK authorised biocidal products.

Is soft washing safe for plants and pets? Done properly, yes. We protect planting and rinse the surrounding areas afterwards, and runoff is controlled so it doesn't reach surface water drains. We'd ask you to keep pets off treated areas until they're rinsed and dry.

How long does soft washing last? On render, about two to three years with a proper biocide treatment. Shaded, north-facing and tree-covered walls go first. Pressure washing alone often greens back up within a season because the spores survive.

Can you soft wash with a normal pressure washer? Not really. Some machines can apply chemical at low pressure through an injector, but the clean itself depends on the biocide and the dwell, not the machine. A pressure washer used as a pressure washer is the opposite of soft washing.

Does soft washing work on brick? Yes, brick responds well, though heavy soot and carbon staining sometimes needs a detergent stage first. Soft natural stone needs more care with dilution, which is one reason we survey before quoting.

Get a straight answer on your walls

Send us a couple of photos of the worst elevation and we'll tell you what's growing on it, whether soft washing is the right fix, and what the job involves. No obligation, and if it's a renderer's problem rather than a cleaner's, we'll tell you that too.

You can see how we work on our soft washing service page, then 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: 19 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.