Render Cleaning Guide: Removing Green and Black Staining Safely
Quick answer: Render Cleaning Guide
Green and black marks on render are algae, lichen and mould. They should be removed with a low-pressure soft wash and a render-safe biocide, never a high-pressure jet wash. A professional clean usually restores render to near-original colour and lasts 2 to 4 years before it needs a refresh.
Key takeaways on render cleaning guide
- Staining is biological, so it needs a biocide, not just water.
- High pressure can permanently damage silicone and monocouche render.
- North-facing and shaded walls stain fastest.
- Persistent damp patches can point to a leak behind the render.
Why render goes green
Modern through-coloured renders are slightly porous. Algae spores land on the surface, feed on moisture and dirt, and spread. Walls that stay damp because of shade, dripping gutters or overhanging plants stain first.
When staining is a sign of something worse
If a patch stays dark and damp even in dry weather, water may be getting in behind the render from a leaking gutter, downpipe or window seal. In homes with mould and long-term moisture problems, water damage and mould specialists explain how hidden moisture spreads inside walls. Around chimney breasts, cracked masonry is a frequent culprit - chimney and fireplace repair experts can inspect the stack and flashing.
How we clean render
- Test patch to confirm the right solution strength for your render type.
- Soft wash application of render-safe biocide.
- Gentle agitation where needed, then a low-pressure rinse.
- Optional protective treatment to slow regrowth.
Render Cleaning Guide: frequently asked questions
Can all render be cleaned?
Yes. Silicone, K-Rend, monocouche, acrylic and painted render can all be soft washed. The solution strength is adjusted for each type.
How long does render cleaning last?
Typically 2 to 4 years, longer with a protective treatment and if gutters are kept clear.
Will render cleaning remove rust or efflorescence?
Rust and white salt deposits need specialist treatments. We can assess these on a free survey.