Moss, Algae & Lichen
The North West's most common surface problem by a wide margin. Green walls, slippery paths and black lichen spotting — all caused by moisture, and all likely to return unless the water source is dealt with.
If we had to name the single most common reason people call us that isn't graffiti, it's this. Buildings across Greater Manchester and Cheshire go green, and they go green fast, because the region provides exactly what these organisms need: rain, humidity, mild winters and a great deal of shade.
It's worth being clear that this isn't dirt. Algae, moss and lichen are living organisms rooted in or on the surface, and that changes both how they're removed and why they come back. Rinsing off the visible growth without killing what's in the surface is why so many cleaned walls are green again within a season.
Three different organisms, three different problems
Algae is the green or black film on render, brick and paving. It's the fastest to appear and the easiest to remove, because it sits on the surface rather than rooting into it. It needs only moisture and light, which is why a shaded, damp elevation can go visibly green in a single wet season.
Moss is the cushiony growth in paving joints, gutters, roof valleys and at the base of walls. It roots properly, holds a remarkable amount of water against the surface, and in paving it forces joints open. Its real problem is that it keeps the surface permanently wet, which accelerates frost damage and everything else.
Lichen is the crusty grey, white, yellow or orange patching on stone, roof tiles and monuments — a symbiotic organism of fungus and algae, and much more tenacious. It bonds tightly and secretes weak acids that slowly etch the surface beneath. It's the hardest of the three to remove and the most likely to leave a mark where it was.
Green growth is nearly always a water problem wearing a disguise. Before booking a clean, look above the growth: a leaking gutter joint, a blocked hopper or a failed sill sits directly above a surprising proportion of the green patches we're called to.
Does it actually damage the building?
Algae is mostly cosmetic — it looks poor and it makes a building read as neglected, but it isn't structurally doing much. Moss and lichen are a different matter.
Moss holds water against the surface indefinitely. On masonry that means more freeze-thaw cycling, and freeze-thaw is what spalls the faces off bricks and opens mortar joints. In gutters and valleys it causes blockages, which cause overflows, which soak the wall below and grow more moss. In paving joints it displaces the sand that holds the units stable.
Lichen etches. The acids it produces are weak but it works for decades, and on soft stone or a memorial inscription that's a genuine conservation issue rather than an aesthetic one.
And on any walking surface, all three are a slip hazard. Green tarmac, decking, steps and paving in wet weather are genuinely dangerous, which is why a lot of our school, care home and public realm work is scheduled around exactly that risk.
Building or paving gone green?
We clean and treat organic growth across Greater Manchester and Cheshire — and we'll tell you what's feeding it so it stays gone longer.
How we remove it
Superheated steam is the method of choice on almost every surface, and the reason is the temperature rather than the cleaning. At around 150°C the heat kills spores in the surface, not just the growth on top of it. A cold pressure wash removes what you can see and leaves the root system intact in the pores — which is precisely why jetted paths and walls green up again so quickly.
On durable hard surfaces — car parks, yards, large paved areas — rotary jetting is faster and perfectly appropriate, and we'll use it where the substrate allows. On render, soft brick, stone and timber, pressure is the wrong tool and steam does the work.
Then the step that actually determines how long the result lasts: a biocide, applied after cleaning and left on the surface rather than rinsed off. It keeps working on residual spores for weeks. It costs very little on top of a clean that's already happening, and it's the difference between a clean that holds for one season and one that holds for several.
- Clean with heat — steam kills spores, cold water only rinses growth away
- Clear the joints and channels where moss is holding water against the surface
- Apply a biocide after cleaning and leave it to work
- Identify the water source — gutter, hopper, sill, splashback or aspect
- Plan a cycle rather than waiting for it to get bad again
Why it comes back, and what actually helps
Nothing keeps an outdoor surface in the North West permanently free of organic growth. Any contractor promising that is overselling. What varies enormously is how long the result lasts, and that comes down to three things.
Was it killed or just removed? Steam plus biocide buys years. A cold rinse buys months.
Is something keeping the surface wet? A leaking gutter, a blocked hopper, a path built up above the damp course, a sill with no drip — fix these and the growth pattern usually disappears with them. We photograph and flag what we spot, because a small repair often saves several future cleans.
Is it on a cycle? Sites cleaned on a planned programme never reach the state where they need an intensive clean, so each visit is quick and cheap. Sites left until they look bad need the expensive version, and look poor for years in between.
How To Recognise It
What it looks like
- Green or black film on render, brick and paving, worst on shaded elevations
- Cushiony green growth in paving joints, gutters and at the base of walls
- Crusty grey, white or yellow lichen patches on stone, roofs and monuments
- Slippery paths, steps, decking and playground surfaces in wet weather
What causes it
Dealing with the cause is what stops it coming back.
- Persistent moisture — the single biggest factor in this climate
- Shade from trees, neighbouring buildings and north-facing aspect
- Leaking gutters, blocked hoppers, failed sills and ground splashback
- Porous or textured surfaces that give spores somewhere to root
Surfaces It Affects
Frequently Asked Questions
Why does my building keep going green?
Because the surface stays damp. Aspect is part of it — north and west-facing walls in the North West rarely dry out fully — but a distinct pattern usually points at a defect: a leaking gutter joint, a blocked hopper, a failed sill, or ground level built up against the wall. Cleaning treats the symptom; fixing the water source is what changes the pattern.
Does moss damage brickwork?
Indirectly, yes. Moss holds water against the surface permanently, which increases freeze-thaw cycling — and freeze-thaw is what spalls brick faces and opens mortar joints. In paving it forces joints apart and displaces the jointing sand. Algae alone is mostly cosmetic, but lichen slowly etches stone with the weak acids it produces.
Is pressure washing the best way to remove moss and algae?
Not usually. Pressure removes the visible growth but leaves the spores rooted in the surface, so it returns quickly — and on render, soft brick, stone or timber the pressure itself causes damage. Superheated steam kills the spores with heat, and a biocide applied afterwards is what makes the result last.
How long will it stay clean?
With steam and a biocide, typically a few years on a wall and a season or two on paving, depending on shade and exposure. With a cold rinse and no treatment, often only months. Nothing is permanent outdoors in this climate, which is why most sites we look after are on a planned cycle rather than waiting until it looks bad.
Areas We Cover
We deal with moss, algae & lichen across Manchester, Greater Manchester and Cheshire, including:
Need graffiti gone — fast?
Call 0161 399 5247 or request a free quote. We respond within one working hour.