Full House Render Cleaning - Northampton (September 2025)

One of our projects in September 2025 was cleaning the entire render of a house in Northampton. Across all elevations, we had to address heavy black algae staining. Growth was most pronounced on shaded and north-facing walls. We used a controlled-bleach softwash to treat the render. To slow down regrowth, we also followed with a biocide application.

A quick look at the project

• Location: Northampton
• Date: September 2025
• Property type: Full residential property (all elevations)
• What was the main issue: Black algae staining (Gloeocapsa and general biofilm)
• How did we address the issue: We used bleach-based softwashing at low pressure
• Finish: To slow regrowth, we applied a biocide treatment

The mountain to climb

On rendered properties in Northampton, black algae is one of the most widespread forms of biological growth. It builds up over time and won’t be noticed at first. Only when you compare the original colour to the now-uniformly grey or dark render do you appreciate black algae’s effects. To make it even worse, on textured finishes like silicone render or K-Rend, the algae will embed into the surface profile - removing it is no walk in the park.

In this case, the worst staining was on the shaded faces and beneath the roofline, where moisture retention is typically highest. The front elevation was no better. Kerb appeal was definitely gone. Around windows and downpipes, dark, unsightly vertical streaks from the runoff would only make the already discoloured surface look worse.

We knew what to do next

First thing, we protected doors, windows, and all sensitive areas. To protect nearby plants from any runoff, we watered down all adjacent plant beds. Across all elevations, we applied a sodium hypochlorite (NaOCl) solution. Then we waited - dwell time is key for the best results. The solution needs time to break down the algae and biofilm. There was no need for high-pressure washing - it only damages render finishes.

Working top to bottom, we carefully rinsed every elevation. We gave extra attention to areas with stubborn staining. Around windows, under the roofline, and near downpipes - our teams went over them more than once. Where necessary, we reapplied the treatment to achieve a consistent finish.

With the render cleaned and rinsed, we applied the biocide treatment across all surfaces. It inhibits algae and other biological growth from returning. Between washes, the walls will stay cleaner for longer.

The end of the line

Across all elevations, we removed all black algae staining, so the render had a brighter, more uniform look - as close as possible to its original colour. All streaking around windows and downpipes was gone, and we brought the shaded elevations in line with the rest of the property. No exterior clean is complete without a biocide application to extend the durability of the results and slow regrowth. It’s vital.

Related Services

• Render Cleaning