How to remove stains from render?

We frequently see homeowners frustrated by unsightly stains and discolouration on their render walls. While render can stain for various reasons, the good news is that most stains can be cleaned or removed with the proper methods. Here’s an overview of some of the most common render stains and how to eliminate them:


Efflorescence (Water Stains)

Efflorescence refers to the white salt stains that can appear on render walls when water is able to seep through the wall. These water stains are caused by moisture in the wall that evaporates and leaves behind mineral salts from the materials in the render or substrate under the render.

To remove efflorescence, clean the affected render area with a pressure washer or chemical cleaner to wash away the surface salts. Then, apply an efflorescence inhibitor product, which will seal the render and help prevent future moisture penetration that could lead to repeat staining.

For severe or recurring efflorescence, it may be necessary to address any excessive moisture in the wall or foundation that is causing the staining.


Moss, Mould & Mildew

Fungal growth like mildew, moss, and mould thrives in warm, damp, and humid conditions. To prevent stains on render from these fungi, ensure adequate ventilation and airflow around the home’s exterior. For existing fungal stains, clean the render with a diluted bleach or vinegar solution.

For heavy or persistent fungal growth, professional cleaning may be needed to fully eliminate the stains. As with efflorescence, it’s important to address any underlying sources of excess moisture in the home that could lead to repeat fungal growth and staining.

black stains on render


Like mildew, algae tend to grow in damp, humid environments and on surfaces that remain wet for extended periods. Remove algae stains with a pressure washer and algaecide or commercial algae remover. For persistent algae, scrubbing or repeat applications may be necessary. As with mildew, it’s important to eliminate sources of moisture to avoid repeat algae growth.


Rust or Water Runoff Stains

Rust stains are often caused by metal fixtures or frames in contact with or close to the render. Water runoff stains can occur from gutters or downspouts draining onto the render.

To remove these stains, clean the area with a chemical stain remover or oxygen bleach. For stubborn stains, scrubbing or repeated applications may be required. It’s also a good idea to repaint or seal metal fixtures and redirect water runoff to avoid repeat staining.

soft washing render cleaning

Soap Scum

Soap scum stains are caused by built-up soap residue from bathing or washing. Remove these stains by scrubbing the area with an abrasive sponge or non-abrasive scrubber and an algae or grease-fighting dishwashing detergent. For heavy soap scum buildup, a commercial stain remover may be more effective. Be sure to rinse the area thoroughly when finished to remove any remaining detergent residue.

With the proper removal methods, you can eliminate common render stains and keep your exterior walls looking their best. For persistent stains or if you’re unsure of how to proceed, consult our professional render cleaner for advice.