How to clean green algae from K-Rend
Green on a rendered wall is living growth — algae establishing on a surface that stays damp long enough each day for it to take hold. It is not a fault in the render, and it says nothing about how well the house was built.
It also will not scrub off in any lasting way. Removing the visible green without treating the growth means it is back within a season.
Why some elevations are far worse than others
It is normal for one wall of a house to be heavily green while another looks almost new. Drying time is what makes the difference.
- North-facing walls get the least sun and stay damp longest
- Walls shaded by trees, fences, hedges or a neighbouring property
- Sheltered corners, reveals and areas behind downpipes
- Anywhere below a leaking gutter joint or an overflowing gutter
- The lower metre or so of a wall, where rain splashes back off hard surfaces
How the growth is removed
The wall is soft washed. A cleaning solution is applied at low pressure and given time to work on the growth rather than being forced off the surface, then the elevation is rinsed down evenly from top to bottom.
Working a full elevation at a time matters. Cleaning a wall in patches leaves tide marks along the joins that are more obvious than the original staining.
What is done before anything is applied
The finish is looked at first — condition, texture, any patched or repaired areas — and a small, less visible section is tested first where the wall or the staining is unusual. Care is taken around windows, doors, seals and adjacent planting.
Stopping it coming straight back
If the green traces a line down from a gutter joint or a downpipe, the wall will stain again no matter how well it is cleaned. Clearing the gutters at the same visit deals with the cause as well as the symptom.
Shaded elevations will always green up sooner than sunny ones. That is worth knowing when you decide how often the house needs doing.
Want it looked at properly?
Send a few photographs of the elevation along with the address, and Rob will tell you what can realistically be improved, what it will cost and when it can be done.