Red Streaks on Render
The call that started it all. “I have red streaks on my render,” the new homeowner said.
“We just moved in, and it looks like someone wiped a paintbrush on the wall.”
One Tuesday morning in March 2025 my phone rang.
She insisted the marks weren’t there when she viewed the property in September 2024.
I promised to pop over that afternoon.
First Impressions
The streaks looked like dried red paint, but I already suspected something else.
What the ‘paint’ really was.
Trentophilia is a fast‑growing red algae that thrives on rendered walls rich in crushed limestone—its favourite food.
Why Trentophilia shows up.
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Porous render absorbs moisture.
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Crushed limestone supplies the minerals the algae loves.
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Damp, shaded areas let spores settle and spread.
How to remove it—and keep it away.
- Soft‑wash the wall with a soft wash solution.
- Rinse at low pressure to avoid etching the render.
- Apply a breathable sealant to limit future regrowth.
- Trim back vegetation to improve sunlight and airflow.
Quick tip: Schedule an annual inspection each spring to catch early signs of Trentophilia.
When you have the budget, using a Render Care Hydrophobic Coating will give long lasting results.
Need help?
Call us on 0800 1577484
