Logo build-repair.com

Algae On The Facade

Table of contents:

Algae On The Facade
Algae On The Facade

Video: Algae On The Facade

Video: Algae On The Facade
Video: The bioenergy facade: Designing a living façade that cultivates energy from algae 2023, November

Fungi and algae grow on all surfaces. Find out here how you can avoid them on the facade.

The question often arises whether algae and fungal infestation may occur if high-quality facade coatings were used or whether everything was done correctly by hand. Regardless of the legal perspective: Yes, that can happen. Neither the craftsman nor the color are the cause. The fact is: Nobody can predict when an infestation will occur, even if all possible defense mechanisms have been considered to prevent algae and fungal attack.

Fungi and algae grow on all surfaces, regardless of whether rough or smooth, dense or absorbent, whether mineral or organic, whether insulated or not. It just needs to be a little damp and warm enough to have food to grow. Then the spores are able to colonize and multiply everywhere. Against this background, the only thing that really should be avoided is the livelihood of fungi and algae. But is it really that simple?

Fungus infestation above the tilted window. The warm indoor air flowed up the cold facade. The humidity condensed.

Food base

In facade coatings, the ingredients that could serve as food are avoided as far as possible or made difficult to access. This takes place in high-quality plasters and colors. However, there is always food available in the area that is brought in by the wind in the form of pollution. This basis cannot therefore be avoided.

The temperature cannot be influenced, as it is always warm enough except for short periods over the winter. The fact that the winters in Germany are now often very mild exacerbates the situation.

There is also little influence on rain and condensation. In particular, the moisture in the condensation is important because it remains on the facade surface longer than the rain. The drying of the surface can be accelerated through intelligent moisture management of the facade coatings, which inhibits growth. It should be noted that a surface that is dry on the surface may still have enough moisture to allow algae and fungal attack. Growth is no longer possible until the aw value (water activity) is 0.8. The aw value corresponds to the value of the relative air humidity of 80 percent. Moisture can be reduced as the basis for growth, but cannot be avoided entirely.

Algae and some fungal infestation on the weather side due to the proximity of the field and thus increased infection pressure.

Avoid infestation

However, the facade is only affected if there are spores of the fungi or algae, in addition to all of the growth bases mentioned above (also known as infection pressure). It is therefore not possible to reliably predict whether and when an infestation will occur. There are two fundamentally different measures to prevent infestation:

  • The growth of fungi and algae is prevented by high alkalinity (lime, cement, silicate) or biocides (film protection).
  • The basis of growth "water" is withdrawn.

According to the current state of science, the addition of special biocides in facade paints and plasters is still the most effective method. The combination and selection of the biocides in an optimally formulated coating is also decisive here. One speaks of film-protected facade coatings. The equipment is only possible for pasty products based on dispersion, silicone or silicate. In mineral plasters, organic biocides are not sufficiently stable in the matrix. For years, Caparol has been accompanying objects that have been coated with film-protected facade coatings. After far more than 15 years, it can be concluded that these objects come almost without damage over the warranty period of five years.

Since the use of biocides in facade coatings is controversial, the question of an alternative quickly comes into focus. Since both fungi and algae no longer grow above a pH value of nine to ten, the use of highly alkaline mineral plasters (lime, cement) and silicate plasters / paints (water glass) would be obvious. Experience shows that these are very effective and infestation is definitely delayed significantly. However, due to weathering, the alkalinity decreases within six months to a year so that this concept no longer works with sufficient certainty. In the case of silicate paints, there is a chalk that removes any possible infestation with the rain and wind. The use of alkaline products is effectivehowever, this leads to a delay of at most about a year. After using film-protected products, it is an effective but weaker variant.

Algae infestation on balcony railings: The approx. 10 year old facade with film-protected silicone resin facade paint (ETICS) is free from attacks.


Another alternative is facade coatings, the surface of which dries as quickly as possible after rain or condensation. There are various approaches to this. Whether a facade should be hydrophobic or hydrophilic, whether water should be stored in the plaster or other concepts to keep the surface dry for as long as possible is a subject of controversy among experts. Once again, extremes are rarely the right answer. Caparol has therefore always relied on a capillary-hydrophobic facade surface as the most efficient solution. Many objects clearly show that. Due to the capillary hydrophobicity, the water is distributed in a uniform film over the facade without water drops forming. This accelerates drying and is even. This process takes significantly longer with water drops.

The idea of including moisture in the coating system and thus keeping the surface dry is not convincing. Water in the system always means a higher risk of damage, such as frost damage. And water is distributed evenly, ie there is always an increase in the moisture content on the surface. In this respect, this hydrophilic surface is also not a working solution.

The further development of nano-quartz-grid technology (NQG) with an expanded functionality of moisture management actively accelerates the drying of this surface. The combination of capillary hydrophobic surface and accelerated drying is the innovation. This means that the facade is dry longer and therefore has a reduced risk of infection. If NQG is combined with an alkaline product, the alternative prevention against infestation by algae and fungi is optimal. The performance comes very close to film-protected products.

Algae infestation due to high infection pressure and increased moisture in the dense planting.


The most important principle to prevent the development of fungi and algae is water withdrawal. With the products of NQG technology (e.g. AmphiSilan), the moisture management is geared to the quickest drying. In order to actively prevent the growth of fungi and algae, high alkalinity must be supplemented with silicate products (e.g. Sylitol NQG). This effectively slows down the growth of fungi and algae. If you want more security, you can't avoid film-protected products.

Lichen only form when fungi and algae are present.

Source: Malerblatt 07/2016, author: Franz Xaver Neuer, photos: Caparol Farben Lacke Bautenschutz