Green algae or green mould quite often grows on the side of properties. When you spot algae growth on your rendered walls, it can be quite a shock.

Often, people instantly start trying to plan how to get rid of the organic growth on their render, and start cleaning render with things like bleach or a pressure washer in an attempt to get their property looking as good as new.

Unfortunately, taking the wrong approach to removing green algae and mould from your rendered walls can actually damage the exterior surface.

It is crucial that you know which cleaning process will effectively remove organic growth (both green and red algae) without causing any damage to the facade.

If you’ve got green algae on your walls, here’s some tips from Render Hero on what to do.

Try and remove the green algae with a simple cleaning process

Just like any surface, you can sometimes clean rendered walls with simple soapy water. If you’ve spotted algae growth early on enough, you might find that this will remove algae.

Simply get a bucket of soapy water (washing up liquid tends to work well, try and avoid using bleach) and a sponge and scrub the walls.

Do not scrub the rendered walls too harshly, as this may lead to damage, and try not to soak them with water as you may lead to more algae growth or mould later down the line.

Use a biocide

Algae and mould are what is known as organic matter or biological matter. To remove them, and prevent their return, you have to kill any mould spores or algae spores that are around.

Even after you’ve removed green and red algae from the surface, you need to work to kill the remaining algae. Biocides can help you to do that.

You can buy biocides online or in hardware stores, and all you will need to do is follow the instructions on the bottle.

Usually, you will be told to make a cleaning solution with diluted biocide, and to apply it to the algae growth evenly. But be sure to look for specifics before you begin.

Steam cleaning or soft wash

If the biocide doesn’t work, you can try steam cleaning the dirty render in order to remove algae, or you can try a soft wash.

These two methods are similar to pressure washing, but they do not have the same risks of damage to render and stone surfaces as they are not high-pressure.

Steam cleaning uses high-temperature steam to remove algae and mould. Soft washing uses biocides and other chemicals to remove algae without relying on the high pressure like pressure washing.

You will need specialist equipment to steam clean render or soft wash it. Alternatively, you can hire a professional who has experience removing algae, and who will have the necessary equipment.

Apply a biocide topcoat

Once your walls are clean, it’s worth investing in a biocide top coat. This will make removing algae worth it, as it will help to stop the algae from regrowing.

This in turn helps to keep your property looking clean and prevents you from having to engage in the cleaning process all over again!

What not to do when cleaning algae growth from rendered walls

As mentioned above, there are a few things that you should never do if you’re cleaning rendered walls or soft porous walls.

Walls are often easier to damage than we think, and if the damage does occur, it can often be incredibly expensive to repair. To avoid having to repair your walls, you should not:

Use bleach on rendered or painted walls

Bleach is a very strong chemical, and it has a tendency to discolour and ruin things – including paint and render.

When used to clean walls in very dilute concentrations, it doesn’t do harm, but it’s very easy to miscalculate when diluting bleach, and once you’ve put it onto the surface, there’s no going back!

If you are insistent on using bleach to remove algae or mould, you should always be sure to test your cleaning solution on a small patch of unnoticeable render before you continue to clean the whole wall.

This way, if there are any issues with the bleach solution, you won’t have ruined the entire surface!

Use a pressure washer

Pressure washing can be a great tool when it comes to cleaning an outdoor surface but when it comes to rendering it is just not worth the risk.

Rendered walls are flexible, and too much pressure from a stream of water may lead to it cracking or breaking. You might not even notice that it has. 

Once there is a hole in the render, water can seep beneath. This can then lead to mould growth under and on the render, and can cause issues with damp in your home.

The water may then freeze in the cooler months, and this can cause your render to crack further.

Leave the algae growth

You might think that the outside of your home isn’t important, or that a wall is just a wall so it doesn’t matter if there’s algae on it. Bu, in reality, algae growth on your wall can lead to long-term damage. Just like water damage, this can be costly to fix.

It’s always better to be safe than sorry, and usually if you catch algae growth early enough, you can stop it in its tracks. Biocide washes also help to prevent regrowth, which can relieve some stress going forward!


Please enter your comment!
Please enter your name here