Illustrative comparison; not a verified customer job.Algae likes damp, shaded surfaces
Spores are present outdoors and can settle on render. North-facing sections, walls behind dense shrubs and areas below leaking gutters may hold moisture longer, creating conditions for visible growth.
Look for a pattern in the staining
Green below a gutter could indicate an overflowing joint. Vertical streaks beside a downpipe may point to a leak. Widespread fine green patches might be linked to shade and weather. None of these patterns proves the cause without inspection.
Check for other types of marks
Black deposits may be mould or atmospheric grime, while orange and brown marks might have a different origin. Do not apply stronger chemicals simply because the colour is darker.
- Photograph the wall on a dry day
- Look for cracked render and failing seals
- Inspect gutters from a safe position
- Keep plant growth from trapping moisture against the wall
- Get advice on a render-compatible treatment
Prevent repeat staining where practical
Routine gutter maintenance and addressing damp sources can make a difference. If algae returns, a specialist can advise on approved treatment or a suitable cleaning schedule. No product can promise that a sheltered, wet wall will never go green again.
Helpful answers from manufacturer and UK industry guidance
Short answers with links to check the supporting guidance.
Why does white render go green on one side of the house?
One elevation can stay damp longer because it receives less sunlight, faces prevailing weather or sits beside trees and hedges. K Rend notes that algae is common where surfaces remain damp and that nearby sources of spores may increase growth. Start by checking moisture sources and drainage.
Will green algae on render disappear without cleaning?
Some marks may fade when surfaces dry, but established algae and its staining do not necessarily clear just because the weather improves. K Rend advises occasional light maintenance and algae-specific products when growth is present. Check the wall’s condition before selecting a treatment.
How can I slow down algae returning on my render?
There is no permanent promise against regrowth. Keeping gutters and downpipes working, reducing persistent splashback and trimming vegetation away from damp façades can help manage the conditions algae likes. Follow the render manufacturer’s cleaning and aftercare advice.
Frequently Asked Questions
Is green render always algae?
Algae is a common cause, but staining should be identified before treatment.
Can new white render go green?
Yes. Surface growth can appear even on relatively new finishes when conditions are persistently damp.
Will painting over the green fix it?
Painting without identifying and dealing with contamination or moisture can conceal rather than solve the cause.