Rendering exterior walls is an excellent way to get a smooth and modern look for a property. 

It lasts for many years and keeps its appeal well, whether you’ve chosen a coloured or plain render, but as it’s porous it does need to be maintained every so often. 

This is because render can provide a suitable environment for vegetation like moss, algae, lichen, and ivy to grow, leaving your render looking green or yellow.

The render can also promote the growth of organic materials, which can often appear as black mould. 

If left unattended, this vegetative growth can damage your render and spoil your home’s visual appeal. 

There are many ways to clean rendered walls, but you need to judge the condition of it before you take action. 

In this guide, we’ll show you the best ways to clean render to restore your property’s kerb appeal. 

It’s a great home maintenance project for autumn before the winter weather can make the situation worse.

How to clean a rendered wall by hand

If you notice your render has become discoloured or is growing green or black algae, then you can wash it yourself by hand. 

Discolouration usually appears at the bottom of walls where rainwater splashes onto it, creating the humid environment needed for vegetation to grow. 

If it’s within reach, you can use the following steps to clean it, but if it’s higher up the wall then you might need to call in a professional 

Here are the few essential items you’ll need to clean render. 

A regular garden hose and a stiff broom will do, but you should also fill a bucket with warm water and use a scrubbing brush for difficult areas. 

To kill the vegetation and stop it in its tracks, you should buy a biocide product that you can add to the water.

A few drops of bleach also help to remove the staining it has caused, but test it on a small area first if you have a coloured render. 

Step 1

Fill your bucket with 2 litres of warm water, then add the biocide and a small capful of bleach. 

Allow it to mix, and be sure to wear rubber gloves when handling these chemicals. 

Step 2 

Take the broom and begin to remove any of the dirt that has accumulated in the area you want to clean.

Dirt particles can run down the wall from the roof, or be splashed by rainwater hitting the ground. 

Do this on a dry day when the wall is already dry before brushing it. 

Step 3

You can use a garden hose to rinse off the remaining dirt from the affected area of render. 

Now, take your scrubbing brush and dip it in the solution. 

Scrub the render until all of the green algae and dirt has been removed. 

Wait 5 to 10 minutes to allow the biocide to work on the render, penetrating the porous surface. 

Step 4

Rinse the wall down with the garden hose, or pour buckets of clean water over the surface to remove the biocide and bleach residue. 

If the render is close to plants in your garden, be careful not to splash your plants with the potentially harmful water.

You can use the broom to help remove the residue from the wall. 

If the wall has been growing moss, take a plastic bag and collect it for disposal.

You should have a clean render wall now, and this method is great for small areas of render, or properties with thin or old render as it’s gentle on the surface. 

If you have a large area to clean and the render is under 10 years old and a regular thickness, then you can consider using the method below to pressure wash it. 

How to clean rendered walls with a pressure washer

Using a pressure washer on a render that is old or already starting to crumble can further damage the render and the wall underneath. 

Before you choose to powerwash your render, make sure that your wall is in good condition. 

If you use a pressure washer on weak render, you could cause serious damage. Then, you might have to render the wall again!

All you’ll need is a power washer with a fan nozzle and some detergent to add to it. 

Pro tip: pressure washing may not be suitable for silicone render. As such, it's best to use alternate methods.

For more on what silicone render is and how much it costs, read our guide on silicone render costs.

Ready? Let's get started.

Step 1

Hook your power washer up to the hose and plug it in. 

Add the detergent and/or biocide to the tank on the pressure washer. You may need to dilute it first (check the instructions on the label). 

We don’t recommend using bleach in a pressure washer, as the spray will splatter your clothes and everything around it. 

Put on some old clothes as the spray from the wall is likely to be dirty from the algae and grime build-up on the render. 

Step 2

Turn the pressure washer on and test it on a small area of the wall to see if it removes the algae but leaves the render intact. 

Don’t use a pin nozzle on the render, but instead choose the fan nozzle to create a wider spray to cover more area. 

Hold the nozzle around 10 cm away from the wall and move it up and down in a line to make sure you cover all parts of the wall. 

Step 3

If you’ve added biocide to the solution, leave it to work for the recommended amount of time.

After that, clear out the detergent tank and finish spraying the wall with clean water to rinse it off. 

If you have removed a lot of algae, you can bag it or use the pressure washer to spray it into a drain. 

If you want a gentler approach between hand washing and pressure washing, then you can always steam clean your render. 

How to steam clean rendered walls

With a steam cleaner, you don’t need to use any chemicals as the pressure and heat from the steam works into the pores of the render to clean it deeply. 

If you’re renting a steam cleaner, choose one that has a high pressure and comes with attachments suitable for cleaning render, such as a brush. 

Step 1

Take a stiff bristled broom and scrub the surface of the render to remove any large chunks of moss that might be growing. 

Doing this also helps to loosen the algae as well, and can make steam cleaning more effective. 

Step 2

Turn the steam cleaner on and test it on a small area on the corner or side of the render. 

You can adjust the settings from low to high until you find the right pressure of steam you need for the exterior wall render. 

It's also possible to set the temperature, which can be at 100°C or above for normal walls, and a lower setting of 80°C for walls with thin or older render. 

Holding the steamer at an angle, work your way across the wall starting with a strip across the top of the area you wish to clean, then work down. 

Step 3

A steam cleaned render wall should dry quite quickly, and if you’ve discovered there is still some discoloration after it’s dried, you can raise the temperature and do it again. 

If algae still remains, then you can apply a biocide by hand with a scrubbing brush. 

Rinse the area with clean water to finish the job. 

How to protect your newly cleaned render

Once you’ve cleaned your render using one of the three methods above, it’s a good idea to protect it. 

This can be achieved by using either a sealant or a specialist hydrophobic coating, which is designed to repel the moisture that algae uses to grow. 

Once the wall is dry, take your sealant or hydrophobic coating and spread it across the wall according to the instructions. 

If you only have a small area of wall showing signs of algae growth and discoloration, we recommend that the whole wall should be cleaned, as it may just not be showing signs yet. 

Cleaning and then protecting the whole wall is a great way to keep your render looking great for many years going forward.

If you fail to protect your render, you may need to replace it. To find out what you'll need to pay, read our guide on the cost of house rendering.

Prefer to have your render cleaned professionally?

If you are reading this guide on how to clean rendering but don’t have the right equipment, then you can rent a pressure washer or call in a professional. 

It’s also a good idea to call in the experts if your render is thin or has been in place for a long time, as using high pressure equipment on these renders can damage it. 

Blasting render with a pressure washer can cause chunks to fall off, and the wall might need to be re-rendered again (at extra cost!). 

When you hire a professional, they will assess your wall first and check the quality of the render so they know which method to use. 

On Yell, you can browse pressure washing services and property maintenance experts who can handle cleaning your render. 

Browse their profiles, read their reviews, and get quotes from several services before picking your favourite.

No time to search? Take a moment to post a free enquiry and local services will contact you directly to discuss your cleaning needs. 

For more DIY guides, cost-saving tips, and home maintenance advice, check out the Yell blog today.