How to stop mould on outside walls — plus when it's a sign of something more serious

external wall with green algae
Knowing the root cause is the first step in figuring out how to stop mould on outside walls (Image credit: Shynearwitch/Getty Images)

With many of us still reporting mould as an issue in the home, it comes as no surprise that mould removal matters. But if you think you've spotted it on the outside walls of your home, you might be wanting to confirm it is mould as well as how to get rid of it.

"The good news is, black, green, blue and even red patches on the outside of your house are often algae rather than mould," says Dave Bendon, director of D Bendon Construction Ltd.

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Dave Bendon

Dave Bendon has over 30 years experience in construction, working on a variety of commercial and residential projects, including listed buildings and older properties that have been subject to damp and water ingress.

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Edward Jonkler

Edward Jonkler is a Property Care Association Qualified Technician, and a British Damage Management Association Technician, focusing on damp and mould issues in homes. 

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Andy Simms

With almost a decade of experience on the front line in construction as a multi-trader, Andy Simms is well versed in many of the damp issues faced by residential home-owners.

Sarah Harley
Assistant Editor

Sarah is Homebuilding & Renovating’s Assistant Editor and joined the team in 2024. An established homes and interiors writer, Sarah has renovated and extended a number of properties, including a listing building and renovation project that featured on Grand Designs. Although she said she would never buy a listed property again, she has recently purchased a Grade II listed apartment. As it had already been professionally renovated, she has instead set her sights on tackling some changes to improve the building’s energy efficiency, as well as adding some personal touches to the interior.