Short answer
Clean render with a low-pressure soft wash and a render-safe biocide — never a high-pressure jet. Apply the treatment, let it kill the algae and lichen at the root over the following days and weeks, and the green and black staining fades without blasting the surface. A professional soft-wash clean on a typical Chester house starts from around £195.
Why Chester render greens over so fast
Rendered walls are everywhere across Chester, Cheshire and the Wirral — from the white-painted semis around Hoole and Saughall to newer estates in Saltney, Blacon and Broughton, and the K-Rend and silicone render on a lot of recent Flintshire and Wrexham builds. They look smart when they are clean, and tired and patchy the moment growth takes hold.
Our climate is the problem. North-West weather sits damp for much of the year, north-facing walls barely dry out, and properties near the Dee, under trees or close to the Wirral coast green over quickly. That green film, the black spotting and the crusty grey lichen are all living growth feeding on a permanently moist surface — which is exactly why a quick blast with a hose or a pressure washer never lasts.
Render is also softer than it looks. Modern thin-coat silicone and acrylic renders, and older painted sand-and-cement, can both be scarred, cracked or stripped by the wrong approach. Get water behind the render and you risk blown patches and damp inside — so the method matters far more than the muscle.
How to clean render safely, step by step
- 1
Check the render and protect the area
Look for cracks, blown or hollow-sounding patches and loose paint before any water touches it. Cleaning will not fix damaged render, and washing over it can make it worse. Close windows, and protect plants, paths and anything below the wall.
- 2
Soft wash, never pressure wash
Apply water at low pressure only — the kind of gentle flow that rinses, not blasts. High-pressure jets force water into the surface, blow out the texture and can strip thin-coat render. For most rendered walls a soft-wash chemical treatment does the real work, not the pressure.
- 3
Apply a render-safe biocide and let it work
A proper soft-wash biocide kills the algae, lichen and black spotting at the root. It is not instant — the growth dies back and weathers off over the following days and weeks, leaving a far longer-lasting result than scrubbing the surface green off only for it to return next season.
- 4
Rinse gently and tidy up
Where needed, finish with a gentle low-pressure rinse to lift loosened growth, then clear up run-off and any debris around borders and paths. The wall should be left clean and even, with no streaks, gouges or patchy bright spots.
Render cleaning — guide prices in Chester & Cheshire
| Job | Guide price | What affects it |
|---|---|---|
| Soffit, fascia and small render area | From £125 | Compact area, easy ground-level access |
| Render cleaning — typical house wall | From £195 | Soft-wash treatment of a standard elevation |
| Full-house render soft wash | From £295 | All visible rendered elevations on a typical home |
| Heavy lichen / black-spot treatment | From £45 | Add-on where growth is thick and established |
| Full exterior refresh (render + roofline) | From £295 | Render with soffits, fascias and gutter exterior |
Use these as a guide for typical Chester homes. The job is confirmed after a few photos or a quick visit, because the render type, the area, the height and access, and how established the growth is all change the scope.
Never put a pressure washer on render — and don't risk a ladder upstairs
A pressure washer is the single most common way render gets ruined: it strips the surface, blows out the texture and forces water in behind, which leads to blown patches and damp. There is no safe high-pressure setting for render. And cleaning upstairs render means working at height — falls from ladders are one of the most common serious DIY injuries in the UK. If the render is above single-storey, cracked or already blown, or you are not sure which type you have, stop and get it looked at before anyone turns a lance on it.
Pressure washing vs professional soft washing
| DIY pressure wash | Professional soft wash | |
|---|---|---|
| Effect on render | Strips texture, gouges and can blow patches off | Gentle on the surface — cleans without damaging it |
| How long it lasts | Green growth returns within a season | Biocide kills growth at the root, so it stays clean far longer |
| Risk of damp | Forces water behind the render | Low pressure keeps water where it belongs |
| Working at height | You on a ladder at the wrong settings — real fall risk | Done safely with the right access and method |
| Typical cost | £40–£70 washer hire, plus your time and the risk | From £195, insured, with a lasting finish |
Frequently asked questions
Can I jet-wash my render to clean it?
No — high pressure is the quickest way to damage render. It strips the surface, blows out the texture and can force water behind the wall, causing damp and blown patches. Render should be soft washed at low pressure with a biocide instead.
Why does the green come straight back after I clean it?
Because the staining is living growth. Hosing or scrubbing only removes what is on the surface, so it regrows. A soft-wash biocide kills it at the root, which is why a proper clean lasts far longer in our damp Chester climate.
How often does render need cleaning in Chester?
Most rendered walls benefit from a soft wash every two to three years. North-facing, shaded or tree-lined walls, and properties near the Dee or the Wirral coast, green over faster and may need it more often.
Is it safe to clean coloured K-Rend and silicone render?
Yes, with the right method. Modern thin-coat renders are softer than they look, so they need a gentle low-pressure soft wash and a render-safe treatment — never pressure washing or harsh scrubbing that can mark the colour.
What makes the price go up?
The area of render, height and access, how established the lichen and black spotting are, the render type, and whether you add the roofline or soffits and fascias to the same visit.