Full House Render Cleaning - Northampton (September 2025)

A full-house render clean on a residential property in Northampton, completed in September 2025. The property was heavily affected by black algae staining across all elevations, with the most concentrated growth on shaded and north-facing walls. The render was treated using a controlled bleach-based softwash, followed by a biocide application to help slow regrowth.

Project Overview

• Location: Northampton
• Date: September 2025
• Property type: Full residential property (all elevations)
• Main issue: Black algae staining (Gloeocapsa and general biofilm)
• Method: Bleach-based softwash at low pressure
• Finish: Biocide treatment to slow regrowth

The Challenge

Black algae is one of the most common forms of biological growth on rendered properties in Northampton. It builds up gradually - often barely noticeable at first - until the render looks uniformly grey or dark compared to its original colour. On textured finishes like K-Rend or silicone render, the algae embeds into the surface profile, making it harder to shift than it appears.

On this property, the staining was heaviest on the shaded faces and beneath the roofline, where moisture retention is highest. The front elevation was also affected, creating a visible impact on the property's kerb appeal. Runoff patterns around windows and downpipes had left darker vertical streaks on an already discoloured surface.

Our Approach

1. Preparation and protection - Windows, doors, and any sensitive areas were covered or managed before starting. Plant beds adjacent to the walls were watered down to dilute any runoff from the cleaning solution.
2. Bleach-based softwash - We applied a sodium hypochlorite (NaOCl) cleaning solution at low pressure across all elevations. The solution was allowed to dwell for the appropriate time, breaking down the algae and biofilm without the need for high-pressure washing, which can damage render finishes.
3. Controlled rinse and uniformity checks - Each elevation was rinsed methodically from top to bottom. We checked for any areas where staining was more stubborn - particularly around windows, under the roofline, and near downpipes - and re-treated where needed to ensure a consistent finish.
4. Biocide treatment - After the render had been cleaned and rinsed, we applied a biocide treatment across all surfaces. This helps to slow the return of algae and biological growth, keeping the walls looking cleaner for longer between maintenance washes.

Results

• Black algae staining removed across all elevations
• Render returned to a brighter, more uniform appearance closer to its original colour
• Streaking around windows and downpipes cleared
• Shaded elevations brought in line with the rest of the property
• Biocide applied to extend the clean finish and slow regrowth

Related Services

• Render Cleaning