Red Staining on Render: Causes and Safe Removal

By Mark Cave November 07, 2026 |

What Causes Red Staining on Render? Red staining on render is commonly caused by algae that produce orange-red protective pigments, particularly algae associated with the genus Trentepohlia. These organisms colonise exterior walls where moisture, suitable surface conditions and environmental exposure allow them to grow. However, rust from metal fittings, iron-bearing...