Why is white render more prone to algae growth?

The colour of the render may seem unimportant on the surface.

Still, let’s analyse how buildings and houses have been painted over the years in different regions of the world. We can see that, depending on the location, sometimes they are white and sometimes the opposite – darker colours.

The United Kingdom, due to its location and climatic conditions, is very specific.

High levels of humidity and rain are the norm.

From the perspective of historic buildings, it is easy to see that the colour white was not popular in the past. Nowadays, it is becoming fashionable, but unfortunately, this is associated with certain risks.

The main problem is the surface temperature of the coating.

As we know, white reflects light but black absorbs it. Therefore, we tend to wear light-coloured clothing in summer and darker clothing in winter.
We say that dark colours “heat up strongly” in the sun.

And it is precisely the question of this heating that is crucial for the occurrence and growth of fungi.

The surface temperature of white renders and paints is equal to the ambient temperature.

The darker the colour, the higher the temperature.

In the case of very dark/black colours, even when the ambient temperature is a few degrees, the surface temperature on the facade can reach several tens of degrees.

This temperature is the key to the answer as to why white render tends to mould more quickly.

After rainfall, water remains on the surface and evaporates very slowly when white is used. It is under these conditions that the fungus starts to develop.

Even if the product has fungicidal properties and these kill the fungus spores, they can remain in the porous render and form a separation layer.
After the next rainfall, the fungus spores will start to develop on the surface of the old/removed layer and not on the plaster surface, and thus its fungicidal properties will not be relevant.

With darker colours, this phenomenon is considerably reduced as the temperature at the render surface is higher than the ambient temperature and thus the evaporation of water takes place much faster.

So what are the options if we do not want to give up beautiful white?

  • Firstly, we can accept the fact that fungi may appear and, therefore, regularly clean the façade.
  • Another solution is to use Terrix ST- silicate renders, which have a very high pH value so that the fungus does not have a chance to develop, even in the case of white colour.
  • The last possibility is to repaint the facade with Terrix EC-PS or EC-ST. This will make the surface less porous and, therefore, less likely to retain water.

Terrix polymer-silicate or silicate renders are much more effective than the use of acrylic or silicone-based renders and paints.

Acrylic and silicone products only can be protected against fungal growth by adding a biocide to the product. As the biocide is slowly released into the surface after a few years of use, it is depleted, and the render no longer has any protection.

All Terrix ST and PS renders and paints are naturally protected against algae growth by an elevated or high pH level.

The high pH level reduces or completely excludes the possibility of algal and fungal growth. It is a natural protection whose effectiveness is not time limited.

We recommend contacting our technical advisers to discuss the most effective solution for your project.

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