Why Is My House Turning Red? The Truth About K-Rend, Algae, and Soft Washing

Jan 11
3 min read

Have you noticed red, green, or even black stains starting to appear on your beautiful rendered walls? If you have looked up at your home recently and thought, "It looks like it needs a paint," you are not alone.

Thousands of homeowners across Leicestershire and Northamptonshire face this exact problem. But here is the good news: It’s not dirt, it’s not permanent, and you definitely do not need to paint over it.

Those stains are actually a living infection called Red Algae (Trentepohlia). At Eazi Cleaning Solutions, we help homeowners restore their property's original brightness without the massive cost of repainting. Here is everything you need to know about why your walls are turning red and how to fix it safely.

Close-up of red algae stains on K-Rend wall.

What is Causing the Red Stains on My Walls?

Modern renders—like K-Rend, Weber, Monocouche, and Pebble Dash—are incredibly popular on new builds and extensions. They look fantastic when new, but they have a unique characteristic: they are designed to breathe.

Because the surface is porous (like a sponge), it holds onto small amounts of moisture. In the damp UK climate, this creates the perfect breeding ground for airborne spores:

Red Stains: This is usually Trentepohlia, a type of algae that produces a red pigment to protect itself from the sun.
Green Stains: Typically green mould or common algae found on shaded walls.
Black Stains: Often a sign of black mould or atmospheric pollution (carbon) from busy roads.

This isn't just a cosmetic issue. If left untreated, the algae roots deeper into the render, which can eventually cause frost damage in winter.

Can I Just Pressure Wash It Off? (The Danger Zone)

This is the most common mistake we see. When homeowners see dirt, their instinct is to blast it with a high-pressure washer.

Please do not do this.

High-pressure washing is too aggressive for modern render. It can strip the delicate surface finish, leaving "stripes" on your wall or even blowing chunks of the render off entirely. Worse still, water alone does not kill the root. You might blast the visible red off, but the spores remain deep in the pores. Within 6 months, the algae will grow back thicker and faster than before.

Before and after soft wash render cleaning results with Eazi Cleaning Solutions.

The Solution: What is Soft Washing?

At Eazi Cleaning Solutions, we use a specialist technique called Soft Washing. As the name suggests, it is gentle—we use no more pressure than a standard garden hose tap.

Instead of relying on force, we rely on science:

Application: We apply a biodegradable biocide treatment to the wall.
Activation: This solution soaks into the pores of the K-Rend or Monocouche, killing the algae and mould spores at the root.
Rinse: We gently rinse the dead organic matter away using low-pressure steam or water.

The result is a wall that is not just visually clean, but microscopically clean. Because the root is dead, your walls stay cleaner for years, not months.

Cleaning vs. Painting: Which is Best?

We often get called to properties where the owner was days away from booking a painter. Painting over dirty render is often a bad idea for two reasons:

The Cost: Scaffolding and professional painting can cost thousands of pounds. Soft Washing is typically 70% cheaper than painting.
Breathability: Painting seals the surface. If you paint over a breathable render like K-Rend, you trap moisture inside the wall, which can lead to damp issues inside your home later on.

Cleaning restores the wall to its original, breathable condition.

Recent Results in Leicester & Northampton

We have been busy restoring homes across the Midlands. From removing green mould on north-facing walls in Loughborough to clearing stubborn red algae in Wellingborough, the transformation is always satisfying to watch.