Algae And Mushrooms On Facades: It Is So Green

The good news first: All paint and plaster manufacturers are largely in agreement on the causes of algae and fungus formation on facades. However, there is disagreement about which system is most effective in protecting against it. Josef Schneider If we were to look for solutions to the algae and fungus problems on facades, we could make it easy for ourselves and - as with Günther Jauch - try the public joker. Then we would only have to leaf through a few pages in this issue and find the result of an online survey there (see “Voting of the month”, page 85). According to this, around a third of the respondents recommend their customers "in any case a biocide additive". This coincides with the statements of the manufacturers we surveyed, according to which the majority of their artisan customers use systems containing biocides. In this case, this article would conclude with the conclusion: "Biocides protect most effectively against algae" at this point. But the topic is too complex to be left alone. Because biocides are by no means the only solution.

Causes of algae and fungi

The most important prerequisites for the formation of algae and fungi are moisture, daylight, carbon dioxide and nutrients. Therefore, they occur mainly on west and north facades and in the plinth area. Plant growth in the vicinity of the building favors the formation of algae. "Algae and fungus growth on facades is primarily a purely aesthetic problem," emphasize Kirstin Willers and Albert Klein von Brillux. "We are not aware of any direct damage to the paint or plaster caused by algae growth." A view shared by Franz Xaver Neuer, Head of Technology at Caparol. "As long as the facade coating is intact, i.e. has no plaster and paint damage, there is only a surface and visual appearance of fungi or algae. The facade coating underneath is not damaged.“Nevertheless, the topic is and remains a major annoyance, especially for builders. Especially since the algae growth seems to be spreading more and more. For Thomas Koch, Product Manager at Keimfarben, this is "a nice indicator that our air is again much cleaner than it was years ago." Clean air = good plant growth. Benedikt Müller-Wortmann, like many of his colleagues, sees another reason for the increase in the problem. "According to market observation, 75 percent of all insulated buildings are affected," says the Head of Application Technology at CD-Color. The reason for this lies in the fact that the night air condenses more easily on the cooler facade surface of insulated houses and this condensate favors the growth of algae. Especially since the algae growth seems to be spreading more and more. For Thomas Koch, Product Manager at Keimfarben, this is "a nice indicator that our air is again much cleaner than it was years ago." Clean air = good plant growth. Benedikt Müller-Wortmann, like many of his colleagues, sees another reason for the increase in the problem. "According to market observation, 75 percent of all insulated buildings are affected," says the Head of Application Technology at CD-Color. The reason for this lies in the fact that the night air condenses more easily on the cooler facade surface of insulated houses and this condensate favors the growth of algae. Especially since the algae growth seems to be spreading more and more. For Thomas Koch, Product Manager at Keimfarben, this is "a nice indicator that our air is again much cleaner than it was years ago." Clean air = good plant growth. Benedikt Müller-Wortmann, like many of his colleagues, sees another reason for the increase in the problem. "According to market observation, 75 percent of all insulated buildings are affected," says the Head of Application Technology at CD-Color. The reason for this lies in the fact that the night air condenses more easily on the cooler facade surface of insulated houses and this condensate favors the growth of algae.“Clean air = good plant growth. Benedikt Müller-Wortmann, like many of his colleagues, sees another reason for the increase in the problem. "According to market observation, 75 percent of all insulated buildings are affected," says the Head of Application Technology at CD-Color. The reason for this lies in the fact that the night air condenses more easily on the cooler facade surface of insulated houses and this condensate favors the growth of algae.“Clean air = good plant growth. Benedikt Müller-Wortmann, like many of his colleagues, sees another reason for the increase in the problem. "According to market observation, 75 percent of all insulated buildings are affected," says the Head of Application Technology at CD-Color. The reason for this lies in the fact that the night air condenses more easily on the cooler facade surface of insulated houses and this condensate favors the growth of algae.that the night air condenses more easily on the cooler facade surface of insulated houses and this condensate promotes algae growth.that the night air condenses more easily on the cooler facade surface of insulated houses and this condensate promotes algae growth.

Maintenance offers security

But how can you effectively prevent the formation of algae and fungi? There is initially agreement among the experts surveyed. "There is no such thing as long-term protection," is the credo. The skilled tradesman would be well advised if he made this unmistakably clear to the client. "Anyone who promises something different acts dubious," said one expert. Herbol also sees it this way: “We recommend every professional to actively address and document the topic with the customer right from the start. We have a checklist to assess the risk of infestation.”What became clear in our survey: there are no maintenance-free facades any more than there are maintenance-free heating systems or cars. Only: painters and plasterers find it much more difficult than their colleagues from the SHK company or the car workshop,to offer appropriate services. Why actually, when there is argumentation aid from the highest level? In its information sheet on reducing the use of biocides on facades (see box PraxisPlus), the Federal Environment Agency points out that "regular inspection and maintenance of facades should be part of normal building maintenance and contribute to reducing environmental pollution."

Measures against algae

“If you only have a hammer as a tool, you see a nail in every problem.” - This quote from sociologist Paul Watzlawick inevitably comes to mind when you start looking for the most effective remedy for algae growth. Depending on the manufacturer - depending on the product range or the company philosophy - either silicate paints, silicone resin paints, acrylic dispersions, mineral or other systems, in some cases a combination of everything, take center stage. Advantages are highlighted, there don't seem to be any disadvantages. And when talking about disadvantages, they usually affect the products of competitors. That doesn't make it easier for the craftsman - nor for us, by the way; nevertheless we dare an overview.

Constructive details

Anyone who effectively protects a facade from moisture also prevents algae formation. That is a fact. In practice, this is achieved through constructive details in the architecture, for example a sufficiently large roof overhang. This should be taken into account when planning a building. Unfortunately, such measures do not adequately protect against condensation and can only be subsequently implemented with great effort.

Heat regulating systems

The increased heat storage capacity of certain (insulation) materials can protect a facade surface against condensation - and thus against algae growth. The surface stays warm longer when it cools down and therefore stays dry longer than other surfaces. This property is attributed in particular to wood fiber insulation materials and hemp insulation. Incidentally, there is a study by Sto that, according to its authors, proves exactly the opposite (see box PraxisPlus). Product examples: wood fiber insulation from Gutex, Inthermo and Pavatherm; Maxit Solar coating system from Franken Maxit.

Capillary hydrophilic systems

The hydrophilic, i.e. water-friendly systems protect against algae formation based on physical principles by keeping the facade surface as dry as possible. The material structure increases the surface of the water drops many times over. For one, the moisture can evaporate faster. At the same time, the smallest capillary pores in the finishing coat absorb the moisture temporarily and release it again when the humidity drops. Product example: Saint-Gobain Weber Aqua-Balance.

Classic scratch plaster

Almost all mineral and silicate products are based on this hydrophilic principle. Take up water to keep the surface dry - this minimizes the risk of algae. Another effect is added to the classic scratch plaster. By constantly chalking the surface, algae are also removed. Growth, therefore, is delayed, if at all. The material is environmentally friendly and has been tried and tested for centuries. This is contradicted by increased production effort, restrictions in coloring and the problem of partial revision, for example in the event of contamination by graffiti. Product examples: Baumit KratzPutz KRP Jura; Knauf scratch plaster mak3.

Thick-layer plaster systems

The mode of operation of mineral, thick-layered plaster systems As a component of thermal insulation composite systems is comparable to that of a scratch plaster. Moisture is quickly drained from the surface into the subsurface and from there it is released into the ambient air as water vapor. In addition, the thick layers of plaster ensure increased heat storage, which, as described above, also has an advantageous effect. Here too, increased effort in the manufacture of the system, consisting of flush-mounted, top-coat and, if necessary, painting, must be taken into account. Product example: KEIM Aqua- ROYAL ETICS system.

Silicate paints

According to our survey cited at the beginning, silicate paints are the first choice when it comes to protection against algae and fungi. This is no coincidence: their nutrient-free coating film does not provide food for the algae. In addition, the hydrophilic property of the paint film ensures that the facade surface dries faster. Added to this is the alkalinity of the silicate paint. This also protects against organisms such as algae. However, protection is also limited in time for silicate paints, since the pH value drops over time. Product example: Brillux silicate facade paint HP 1801.

Capillary hydrophobic systems

The exact opposite philosophy to the products listed so far is represented by capillary hydrophobic, i.e. water-hostile systems. They are characterized by the fact that they drain little or no water into the subsurface. Rather, it is transformed into a thin film of moisture on the facade surface. It should evaporate as quickly as possible without penetrating deeper into the plaster system or draining away and washing off organic particles.

Silicone resin paints

Silicone resin paints offer very high water vapor permeability and at the same time protect the surface from outside water. A sufficient protection against algae and fungi is in many cases only guaranteed by the addition of biocides, which is why corresponding products are usually equipped with film protection. Product examples: Caparol Thermosan, Caparol Muresko; FEMA-Clean facade paint; ZERO facade 95 silicone resin paint

Hybrid coatings with nano technology

More and more manufacturers are combining binders to combine their different, positive properties in one product. Sometimes the surface is also modified by nanotechnology. This favors the so-called water spreading effect, which turns water drops into a moisture film and thus distributes them homogeneously. Dirt particles are washed off over the entire surface and the surface dries quickly. Product example: Dinova SI-Fusion (color) and Dinova Hybrid scratch plaster (plaster); Herbol Symbiotec; Sakret N-TEColor N-TEC.

Lotus effect

A number of special coatings take advantage of other effects to master the algae problem. Years ago, the Sto company transferred the natural self-cleaning effect of the lotus plant to modern facade coatings. As a result, rainwater rolls off the surface and organic contaminants - including algae - are washed off. Product example: Sto Lotusan.

Photocatalytic systems

Many coatings contain active pigments that destroy and degrade organic substances, including algae, when exposed to light. These are then removed from the facade by wind and rain. The effectiveness of this photocatalytic effect has been known for years. Opinions differ as to whether it is sufficient to prevent algae growth. However, one property is undisputed: the catalytic substances do not degrade. This means that the effect remains in the long term. Product examples: Baumit NanoporColor (paint) and NanoporTop (plaster).

Encapsulated biocides

If it is not possible to do without a biocide, one should only use paints and plasters that contain encapsulated (some speak of "encapsulated") biocides. The Federal Environment Agency also recommends this in the leaflet mentioned above. “Encapsulated” means that the active ingredient is encased in a polymer. The solubility of the active ingredient can thus be adjusted. In addition, the washout rate is reduced. This measure can increase the duration of protection and helps to reduce the release of substances into the environment.

Expert advice makes sense

Even if, according to the latest research results from the Fraunhofer Institute for Building Physics, only a maximum of five percent of the encapsulated biocides are washed out in the first year, a waiver in any case means a benefit for the environment - and thus for all of us. Therefore, the first priority should always be the consideration of dealing with the algae problem either through constructive detailed solutions or the use of biocide-free products. However, this must not go so far as to ignore the causes of algae and fungus formation and to ignore unfavorable conditions in this regard. Well advised is who, in case of doubt, brings his paint and plaster manufacturer on board via the specialist consultants. Algae and fungal growth on facades are primarily a purely aesthetic problem.

Practice plus

Online special: Algae and fungi on the facade You can find detailed interviews with the experts from the paint and plaster manufacturers in our online special on Malerblatt Wissen. There you will also find all the checklists and leaflets mentioned in the article as well as the Sto study and information on the products cited.