Cleaning removes the growth that is there today, but spores keep landing on the wall. A protective treatment helps the render resist them for longer. Most are either a residual biocide, which stays on the surface and kills new growth as it starts, or a water repellent, which reduces how long the wall stays damp. Some products combine both. They are applied once the wall has been cleaned and rinsed, usually at low pressure or with a sprayer.
The right product depends on the render. Silicone render already repels water, so a residual biocide is usually the useful part. Monocouche, sand-and-cement and painted render can benefit from a breathable water repellent, but it must let moisture out of the wall as well as keep rain off, or it can trap damp. Where a render system has a manufacturer's guarantee, check the manufacturer's advice on which treatments are compatible before anything is applied.
What is included
- Advice on whether a treatment is worthwhile for your walls
- Choosing a biocidal, water-repellent or combined product
- Checking compatibility with the render type and any guarantee
- Applying the treatment evenly after cleaning
- Avoiding glazing, paintwork and planting during application
- Guidance on drying time and weather conditions
- Advice on when to re-treat or maintenance clean
Who it is for
- North-facing walls and gable ends
- Walls shaded by trees, hedges or neighbouring buildings
- Rural and coastal homes with heavy algae growth
- Homes where render greened up quickly after a past clean
- Managing agents wanting longer gaps between cleans
How much does it cost?
As a guide, a protective treatment usually adds £1 to £3 per square metre to a render clean, or roughly £100 to £300 for a typical semi-detached house. See our full cost guide.
