I tried using Sugar Soap Professional Strength to remove stain from rendered wall and it worked.
For stubborn stains such as rust, ensure the rusting particle is removed (this can be done with the tip of a knife or tweezers) and scrub clean with industrial strength CLR ( Calcium/Lime /Rust) Cleaner.
More cleaning methods of rendered walls Pressure CleaningTo ensure the finish doesn’t lift during cleaning, clean at 80 - 120 Psi with a fan tip rather than a direct needlepoint spray.
Hand CleaningSome of the best cleaning results are achieved by scrubbing with a stiff broom or brush and hosing as you go, so as not to allow a film of dry grime and residue to form. Otherwise it can be more difficult to remove than the original dirt.
Mould and MildewQuote:If heavy wind driven rain periods are expected, rain may reach areas that are normally dry. High humidity associated with rainy periods prevents rapid drying to occur which yields ideal conditions for the growth of mould or mildew. This may appear as unsightly dark stains (sometimes green or purple) on the surface.
When mould spores settle on a coated surface, they ‘hatch out’ and draw nourishment from the coating itself or from dirt on the surface. Mould reproduces by spores, therefore it is important to apply a residual fungicidal wash such as Acryloc Mould Rid (available through RSA), which remains on the treated surface and kills mould as it ‘hatches’ from the spores.
It's recommended the rendered walls are cleaned every 6 –12 months. Regular maintenance not only makes coating life longer, but also alleviates the need to use harsh and dangerous solvents or acid cleaners on the surface.
