House care
How often should you clean your render?
Leo Grant
· 5 min read
Best season
Spring or autumn
How often
Every 12–24 months
DIY difficulty
Hard, needs care
Pro time
About 4 hours
Why render goes green
Render is slightly porous, so it holds moisture after rain. On shaded walls that moisture lingers, and airborne algae spores settle in and grow. The green haze you see first is the early stage; left alone it darkens into black streaks.
North-facing walls, walls near trees and anything under a dripping gutter go first. Sunny, open walls can stay clean for years.
How often is right
Shaded or sheltered walls usually need a clean every 12 months. Open, sunny walls can go 18 to 24 months. If you live near trees, fields or the coast, check every spring.
Signs it’s time
Look for a green tint near the ground, dark streaks below window sills, or a patchy, uneven colour when the wall is dry. If you can see it from the street, it’s time.
Can you do it yourself?
A pressure washer will make render look clean for a few weeks, but it drives water into the surface, can strip paint and leaves the roots behind. A soft wash kills the growth with a biodegradable cleaner, so it stays clean far longer.
The same wall, before and after one soft wash.
Key takeaways
Clean shaded walls once a year, sunny walls every 18 to 24 months.
Act at the green-haze stage, before black streaks set in.
Soft wash, never high pressure, on render and paint.
Keep reading
More from the journal.
Guides
Pressure or soft wash: which does your surface need?
Concrete loves pressure. Render, roofs and timber don’t. A quick guide to matching the method to the surface.
Seasonal
A spring checklist for the outside of your home
Ten small jobs that stop winter grime turning into summer stains.
Roofs
How to keep moss off your roof for longer
Why scraping alone doesn’t work, and what a biocide treatment actually does.