before and after picture of render cleaning

Why is Wall Render Presenting Problems Today?

Rendering is the process of applying a premixed layer of sand and cement to exterior, and sometimes interior, walls to achieve a smooth or textured finish.

In the past three decades or so, self-finished renders have become extremely popular:

  • Architects liked the variety of finishes they offered – smooth, textured, mica sparkles, and colour pebbles to name a few – that were not so easy to obtain with paint.


  • Householders liked them because of their easy, low maintenance – they need no painting, just a light clean every now and again.


  • Builders liked them because there was no more hanging around waiting for paint to cure before completing the building.


As well as many practical benefits, the benefits don’t stop there. Render also has great waterproofing and fire rating qualities that protect buildings from adverse weather and general wear and tear, so it’s no wonder why it has become so popular.

With this being said however, whilst wall render offers many advantages, there is a common misconception that they are completely “non-maintenance.” Modern render is incredibly hard wearing and may last 20-30 years without a problem, if applied correctly, however, this doesn’t mean that they won’t need some kind of regular cleaning.

Modern Problems with Render

The main problem with wall render is that it tends to get a build up of biological growth on its surface, mainly red or green algae, black marks from fungi and other contaminants. If you’ve ever seen a building or house that has patches of discolouration on its surface, then you know what we mean.

What many people do not know, is that this build up of algae is actually not primarily due to the render itself, but rather due to the introduction of modern wall insulation. As wall insulation has improved over the years, this has reduced the amount of heat moving through the walls and into the render. Therefore, in colder and damp conditions, the render has now become a prime material for microbial growth which stains the surface, meaning that they need to be cleaned with high-quality biocide much more frequently than they used to – usually every three years or so depending on where the property is located.

Remember those patches of discolouration we mentioned? In the patches where growth isn’t occurring, these are areas where the insulation is not so effective and heat is getting through to dry the render. These are usually areas where there are radiators or patchy cavity wall filling.

render walls with algae on them

How to Maintain Your Render

Although this growth is a problem with rendered properties, regular cleaning and preventative measures to minimise the growth again are available.

Soft Washing

Soft washing is the process of using eco-friendly chemicals and a low-pressure wash, which is excellent for cleaning a variety of modern exteriors, from render, brick and natural slate to concrete and slate roofs, even brick drives and concrete paths! As well as being the best cleaning method to use, it also offers two other major benefits:

  • It gives fast, predictable results without damaging the surface, and these results can last for years.


  • It is a cost-effective cleaning method that restores your exteriors to their former glory.


clean render walls

Although it can take a few months for the effects of the biological cleaning to fully cleanse the surface, once restored, exteriors will only need a bi-annual or tri-annual treatment to keep surfaces looking great for longer!

So, although modern insulation causes this problem with rendered buildings, this is a problem that is solved with a good clean. Algae is stubborn stuff and can grow anywhere in the right conditions, therefore nip it in the bud before it spreads and have your surfaces treated to delay it growing in the near future!

What we can do for you….

As specialist cleaners, we feel that a job well done is most important. If you need any advice or further information about render cleaning, feel free to give us a call.

Need more cleaning inspiration or advice? Check out our other blogs…