When we moved into our house, the render was already painted a light sage green. It's a lovely colour, but over time the walls started to look grubby, with green and dark patches spreading across them.

We assumed the whole house needed repainting. It turned out it just needed a proper clean, which saved us a lot of money (and a lot of time up a ladder).

Here's what we did, what it cost, and what we've learned about cleaning, repairing and painting render.

Why does render go green?

Those green, dark green or grubby patches on render are usually algae, sometimes with lichen or mould mixed in. We honestly thought ours was just dirt, and didn't realise it was actually plant life growing on the walls!

It loves damp, mild conditions, and it tends to be worst on the walls that get the least sun and stay damp the longest. On our house, the side walls were by far the worst.

We live about 1km from the sea in Cornwall, so we get mild weather, salty wind and plenty of storms and rain in winter, even though it's one of the sunnier parts of the UK. After high winds, our windows are often covered in salt and sand too.

From a distance, algae can look like faded or dirty paint. That's why so many people (us included) think they need to repaint, when the render underneath is actually fine.

Why does some render go red?

Ours went green and dark green, but you might see render that's red or orange instead. That's usually a different type of algae, and it can look really bad once it spreads.

There are some much newer houses near us that are completely covered in red, and they look awful. Our house was built in 2004, and the man who cleaned our render told us ours wasn't the same type of render used on many new builds.

He said the newer render gets really bad, and that ours is better quality, so it should last a long time before the growth comes back. So far, he's been right!

Our render cleaning cost and how long it's lasted

In November 2023, I found an exterior cleaning company through a local Facebook group. They had great reviews and lots of before and after photos of render they'd cleaned, and the houses looked brand new in their after photos! So I messaged them with some photos of our house.

I asked for the render to be cleaned, along with the gutters and fascias, so it could all be done at once. Their first quote was £450, to soft wash three sides of the house and clear and wash the gutters, fascias, soffits and downpipes.

In the end, I asked them to do all four walls, which brought the total to £600.

Honestly, we only got one quote. I'm not sure whether we could have found it cheaper, but they had great reviews and we didn't know how to do it ourselves at the time.

It took them less than a full day's work, and it made a huge difference. The walls looked back to new, and we didn't need to repaint after all!

Three years on, it still looks good and the growth hasn't started coming back yet. So for us, it was money well spent.

After three years, the render cleaning is still looking good.

What is soft washing?

Soft washing is the most common way to clean render professionally. Instead of blasting the walls with a high-pressure jet, it uses a low-pressure spray and a cleaning solution that kills the algae, lichen and mould.

The solution is usually a biocide. It kills the growth at the root, rather than just removing what you can see, which is why it doesn't come back quickly.

Pressure washing render is usually best avoided. It can damage the surface, especially on older or painted render, and can push water into any cracks.

Can you clean render without chemicals?

This is what I'm looking into for next time. Since our render was cleaned, we've filled the back garden with nine veg patches and fruit trees, and I don't want strong chemicals sprayed right next to our food.

The soft wash also killed off all the plants at the base of our walls, including the mind-your-own-business that had spread over the stones along the side of our house. So I really wouldn't want it anywhere near our vegetables and fruit, and we'll need to come up with another solution, at least for the back of the house near the garden.

We prefer doing jobs like this ourselves anyway, so next time we'll try to find an eco-friendly, non-toxic way to do it and save money too. Options worth looking at include:

• Gentle scrubbing with water. A soft brush and plenty of water can remove light growth, although it won't kill it at the root.
• Biodegradable cleaners. Some render and patio cleaners are marketed as biodegradable or plant-friendly, so check the label and the safety advice carefully.
• Protecting your plants. If you do use a stronger product, cover nearby plants and veg beds, and rinse well afterwards.
• Asking cleaning companies. Some offer more eco-friendly products, so it's worth asking what they use before you book.

If you like making your own cleaners for indoors, here's how to save money by making your own eco-friendly cleaning products.

How to deal with hairline cracks in render

Our render also has a couple of hairline cracks. They're fine, shallow cracks and not structural, which is really common as render expands and contracts with the weather.

Small hairline cracks are usually filled with a flexible exterior filler or crack repair product, then painted over with masonry paint. Anything wider, getting bigger or letting water in is worth getting checked by a professional.

My husband filled one of our cracks himself. The only problem is that the filler is white, and our house is sage green, so it really stands out!

If your render is badly cracked or damaged, it may need patching or re-rendering. You can buy render and repair products from suppliers like Direct Building Products, but bigger jobs are usually best left to a professional plasterer or renderer.

Here you can see the cracks we've refilled, and under the veranda you can also see lots of random places where we've tested paint colours to try and find a colour match, but unsuccessfully!

Painting render: why we're repainting the whole house anyway

Because of the white filler, we now need to repaint. And this is where it gets tricky.

The house was already sage green when we moved in, so we didn't know the original paint colour. We bought lots of testers to try to find a match, but none of them were quite right.

The paint has probably faded over the years in the sun too, which makes matching it even harder. Patching up the crack would have been the cheapest option, but without a matching colour, it would always show.

So we've chosen a close colour that we like, Garden Party by Coat, and we'll eventually get around to painting all the external walls so they're all the same colour.

We'll save a lot of money by my husband doing the painting himself. Paying someone to paint all four external walls of a four-bedroom detached house would cost a lot, so doing it ourselves makes a huge difference.

Tips for painting render

If you're painting rendered walls yourself, here's what to bear in mind:

• Clean it first. Paint won't stick properly to algae or dirt, so clean the render and let it dry completely.
• Fill cracks before painting. Use a flexible exterior filler for hairline cracks.
• Use the right paint. Choose a masonry paint that's suitable for render and lets the walls breathe.
• Buy testers. Try them on a small area and look at them in different light, as colours can look very different outside.
• Pick the right weather. Avoid painting in rain, frost or strong sunshine, and check the forecast for a dry spell.
• Work safely at height. Use proper ladders or a scaffold tower, and don't overreach.

Clean or paint: which should you do?

If your render looks dirty, green or patchy, try cleaning it first. It's usually much cheaper than repainting, and you might find, like we did, that it looks as good as new.

Repainting makes more sense if the paint is peeling or flaking, you need to cover repairs, or you want to change the colour. Either way, keeping the outside of your house well maintained helps protect it, and can help add value to your home by sprucing up the exterior.

It's one of those jobs that's easy to put off. Here are some other property maintenance tasks for homeowners to keep on top of too.

Final thoughts

We were all set to repaint our house, but a soft wash for £600 had it looking back to new, and it's still clean three years later. If your render looks tired, get it cleaned before you spend money on paint.

Now we just need a dry spell for my husband to get painting, and we'll be looking for a more eco-friendly way to clean it ourselves next time. For more ways to cut costs around the home, here are my best money saving tips.