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How does dirt form on the facade?

Causes and risk factors

When it comes to professional façade cleaning and the removal of dirt from house walls, there is no way around us. But how does it get so bad? Is it just an optical flaw or can damage occur in the long run? And is there anything you can do to prevent soiling? We will be happy to answer your questions.

The Cause

The most common cause of unattractive discolouration on house walls is algae and mould. Due to the fact that the finishing plaster is thermally highly decoupled from the masonry, condensation quickly forms on the surface. The moisture generated by the condensation makes the ideal breeding ground for algae and mould spores, which spread quickly and usually shimmer in greenish black or rust-brown shades. Driving rain or the lack of roof overhangs also promote growth.

This is not only unattractive, but can also be harmful to your façade. In the course of its own energy production, the resulting bio-carpet excretes small amounts of acid, which have a corrosive effect in the long term, softening the plaster and making it more porous. In addition, the favoured adsorption of particles and pollutants can lead to deep-seated discolourations. Early cleaning provides a remedy and protects against algae and mould attack.

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1. Construction defects

They are often invisible and mostly underestimated – which is what makes them so dangerous: construction defects. Whether defective pointing or faulty rainwater drainage – they quickly lead to damp spots on the house wall and thus to dirty-looking mould.

2. Vegetation & shade

In the country, shadows are mostly cast by trees and bushes, in the city blocks of shade are cast by adjacent buildings onto the house wall. The wandering sun and shadow create temperature differences on the façade, whereby wet areas need more time to dry, in turn promoting the growth of algae, mould and bacteria.

3. Roof overhang

A roof not only ensures that residents stay dry inside, but ideally also serves to protect the house wall from heavy rain. A sufficient roof overhang means that less moisture is deposited on the façade, thus providing protection against mould and algae growth.

4. Incorrect ventilation

Again and again, unattractive mould spots form on the house façade just above windows. The reason for this is often perpetual tilt ventilation, wherein warm air escapes outside, where it precipitates on the colder outer wall and serves as a perfect breeding ground for fungi and algae growth.

5. Building plinth

For buildings with plaster façades, care should be taken to ensure that a sufficiently high plinth is available. We protect the façade against splashing rainwater by means of an optically contrasted plinth, preferably in a darker shade (splash protection). In addition, this prevents moisture from the ground creeping upwards into the plaster façade and forming a breeding ground for mould, bacterial and algae spores.

6. Geographical position

Where a building is located and how it is aligned can considerably influence algae and mould growth. For example, a building in a rainy or foggy area is more endangered than one in a dry area. There are also variations in growth conditions of mould and algae between coastal and mountain areas.

7. Air pollution

The increased spore contamination in rural regions, as well as the rather poorer air quality (nitrogen oxides, dust particles, ...) in urban areas promote the growth of micro-organisms in equal measure and uniquely shape the type of dirt on the façade. It's a good thing that our partners can professionally take care of any pollution thanks to our HERMES® system.

8. Soiling

Dirt is everywhere. As you well know, in cities pollution is caused by exhaust fumes and the dirt from heavily trafficked roads and major construction sites, whereas in rural areas agricultural and forestry work is an underestimated source of dirt.

9. Thermal insulation and thermal bridges

We insulate our houses so that heat stays in the house and we save heating costs. The other side of the coin, however, is that if the insulation is too good, the temperature difference between inside and outside is too great. Due to the fact that the finishing plaster is thermally highly decoupled from the masonry, condensation quickly forms on the surface. The moisture created by the condensation thus provides the ideal breeding ground for algae and fungal spores. You can see this phenomenon very well at thermal bridges, where heat is transferred from the inside to the outside and the façade dries faster. Algae, bacteria and fungus growth is significantly lower in these areas.

10. Weather conditions

Germany is located in a climate zone characterised by mild temperatures and heavy precipitation. Together, these factors form the ideal conditions for the formation of algae, mould and bacteria on the house façade, especially on the weather-exposed side of the building. But not only in Germany – 2016 was the warmest year since weather records began. In combination with precipitation, algae, mould and bacteria threaten to grow just about everywhere.

What can one do about it?

Algae only need water and light to live and grow. In other words: through natural weather phenomena alone, algae can form everywhere and quickly find ideal growth conditions. This means that potential algae infestation can never be ruled out by 100% despite modern building construction and building technology as well as paints and coatings. This makes it all the more important to ensure the dirt is removed from the façade in good time before it becomes not only a visual but also a dangerous defect. With our unique façade cleaning process, removal is particularly gentle and with our protective disinfectant, we prevent a new, unattractive biofilm from quickly settling on house walls.