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Black stains on rendered surfaces tend to be caused by algae or fungi growth, rain and moisture, carbon stains, and dirt and debris build-up, which can also lead to mould. They are generally harder to remove than red or green stains and can embed more deeply into a building’s structure.

The black stains are unsightly and can be difficult to remove. However, removing them with the correct cleaning materials and techniques is possible.

Continue reading to find out more about black stains on renders and the most effective methods to get rid of them.

What Causes Black Stains on Render?

Black stains on render are mainly caused by excessive moisture build-up, debris and dirt build-up, carbon stains, mould, and algae and fungi growth.

When dust and debris build-up, and then there is heavy rainfall, it can sometimes lead to a stain trail forming. When the sun comes out, it bakes the stains on the walls, making them more challenging to remove and leaving behind a faint shadow, sometimes requiring repetitive or stronger cleaning methods.

Why Black Stains Need to Be Removed

Algae or Fungi Growth

Black stains are usually caused by algae or fungi growth, which is a result of being exposed to moisture and humidity for long periods of time. It can become a real problem if left untreated, as it can break down the render and the actual structure of the wall.

Rain, Moisture and Sun

Rain and moisture can cause black stains to spread further down the rendered surfaces. Once the sun comes out, it bakes the stains into the building surface and further embeds them into the material and structure of the building. This can make the stains more challenging to remove and can also leave a slight shadow.

These black stains not only turn your home into an eyesore, but they can also pose further problems to the structure of the building.

Carbon Stains

Carbon stains are formed by pollution, especially if the home is located close to industrial sites, building sites or streets with heavy traffic.
They can also be formed by burning carbon-based fossil fuels (coal, oil or gasoline).

Not only are carbon stains unsightly to look at, but they also can negatively impact the render’s breathability, which can lead to cracks and a weakened structure.

Dirt and Debris Build Up

Dirt and debris settle on rendered surfaces and can build up to the point where mould begins to form. This black mould leaves deep stains that can lead to issues with the home’s structure.

Ways to Remove Black Stains from Render

  • Softwashing: The softwash cleaning method includes using a specialised detergent or cleaning solution and a spray machine. The spray machine deposits the cleaning solution over the rendered surfaces, leaving it for a reasonable amount of time to sit and soak in. The cleaning solution is then rinsed off using low water pressure and hot steam.
  • Pressure cleaning (power wash): If you use pressure cleaning to clean your render, it is best to use a fan tip instead of a needlepoint tip and to use it at a safe distance from the surface.We recommend using a professional rendering or cleaning company when using the pressure cleaning method, as they know the best settings and practices.

    Although pressure cleaners are very powerful and effective, they can also be potentially harmful on rendered surfaces because if they aren’t used properly, they can strip the rendered material off the walls.

  • Bleach solution: Make up a bleach solution using one part bleach with ten parts water. Apply this solution to the black stains on the walls and let it sit and absorb for a few minutes. Once a few minutes have passed, use a stiff-bristled brush to scrub off the stains. Rinse off any residual bleach or stains using a hose.
  • Household cleaner: Using ingredients you already have at home, like baking soda and water, can be surprisingly effective, and best of all, they don’t cost anything!Apply this mixture to the stains and use a stiff-bristled brush to remove the stains. Rinse off the residue debris using a hose.
  • Algae cleaners: Find render-safe algae cleaning solutions and follow the manufacturer’s instructions closely for the best results.

Important Tips to Remember When Cleaning Render

  • Use a plastic sheet to cover up surrounding plants, driveways, and gardens to protect the surrounding area from any cleaning solutions or chemical runoffs.
  • Also, protect yourself by wearing safety goggles, overalls and gloves.
  • Follow any manufacturer’s instructions very closely.

At Sydney Cement Rendering, we are committed to ensuring your rendered surfaces stay in good condition for as long as possible. If you are worried about any stains that appear on your render, don’t hesitate to contact us at 0402 704 984 or visit our website: https://sydneycementrendering.com/ to find out more about what we offer!