Why Are My Walls Turning Red? (And Why Pressure Washing Won’t Fix It)

If you have driven around St Austell, Truro, or Bodmin recently, you’ve probably noticed a common theme. Beautiful modern homes, particularly those with white or cream render (K-Rend), are being stained by unsightly vertical red or orange streaks.

We get calls every week from homeowners asking: "Is it rust?" or "Is something leeching out of the render?"

The answer is no. It’s a specific type of infestation that thrives in our damp Cornish climate, and if you treat it the wrong way, you could permanently damage your home.

What is that red stuff on my walls?

The red staining is actually a microorganism called Trentepohlia.

Technically, it is a type of green algae, but it produces a strong red/orange pigment (beta-carotene) to protect itself from sunlight. This is why you often see it on the south and west-facing walls of properties in St Austell and Fowey that get the most sun.

Ironically, having this algae on your home is a compliment to where we live. Trentepohlia thrives in clean, humid air. It hates pollution. Because the air quality in Cornwall is so good, this algae spreads rapidly.

The Big Mistake: Why You Should Never Pressure Wash K-Rend

When homeowners see dirt, their first instinct is often to blast it with a high-powered pressure washer.

Please do not do this.

Modern render systems (like K-Rend, Monocouche, or Weber) are "breathable" and have a delicate, textured surface. Here is why pressure washing is dangerous for them:

1. It Destroys the Surface: High pressure can blow the "face" off the render, leaving it pitted and rough. This rough surface actually holds more water in the future, making the algae grow back faster.

2. It Causes Damp: blasting water at high pressure can force moisture deep into the substrate of your walls, potentially causing internal damp issues.

3. It Doesn’t Kill the Root: Pressure washing is like a haircut. You might blast the visible red stain away, but the spores remain alive deep in the pores of the wall. Within 6 months, the red streaks will often return, thicker than before.
   

The Solution: Softwashing (The Science of "Sanitizing")

At Bay View Cleaning, we use a method called Softwashing.

Instead of relying on destructive power, we rely on science. We apply a specialised, biodegradable biocide at very low pressure (no stronger than a garden hose).

This solution doesn't just "clean" the wall; it sanitizes it.

1. It soaks in: The solution absorbs into the render, reaching the root of the algae.

2. It kills the infestation: It eliminates the Trentepohlia, black mould, and moss at a microscopic level.

3. Longer lasting results: Because we kill the spores, your walls stay clean for 3 to 5 times longer than they would with pressure washing.
   

Is Softwashing Safe?

Yes. As a family-run business, safety is our top priority. The products we use are fully approved for use in the UK and are biodegradable. once the job is done, the solution breaks down into salt and water, posing no threat to the environment.

We successfully treat properties all across Cornwall, from townhouses in Truro to bungalows in Newquay, restoring them to that "just painted" look without the cost of actually repainting.

Ready to remove the red?

If your home is suffering from the "Cornish red stripe," don't paint over it (the algae will eat through the paint!) and don't blast it.

Contact Joe at Bay View Cleaning today. We are in the St Austell and Truro area every week and are happy to pop by for a free, no-obligation quote.

Bay View Cleaning Expert Exterior Cleaning in Cornwall 📞 07834 991440 📍 54 Pellymounter Rd, St Austell, PL25 4PX 🌐 www.bayviewcleaning.co.uk