Assessment of microbial growth on surfaces

Surfaces exposed to natural weathering will eventually be colonized by microorganisms. Growth traces on façades can lead to a visible discoloration that is often deemed unacceptable and may result in complaints.

Various methods are available to examine the resistance of surfaces to microbial growth. Laboratory methods often fail to replicate real-world conditions accurately. By exposing the samples to the natural climate over an extended period of time (> 1 year), a more reliable assessment of growth resistance can be obtained.

At the test facility in Valley, samples can be exposed to natural weathering conditions. The samples may include:

test specimens that are produced for the investigation according to our specifications or

• façades,
• façade sections,
• complete wall structures prepared by the client's application technicians.

Test buildings are available as supports for façade components or wall structures with typical dimensions ranging from 30 x 30 cm for test specimens to 3 x 2.85 m for façade components or wall structures.

If the performance of façade coatings is to be tested based on orientation, small test buildings are available. These buildings have façades oriented to the main cardinal directions and can be coated accordingly.

The weather conditions at the Valley site (680 meters above sea level) are characterized by frequent freeze-thaw cycles, 1000 to 1200 mm of annual precipitation, and frequent driving rain, predominantly from the west or west-southwest. These conditions put surfaces under severe environmental stress.

Weather data at the test site is recorded using the institute's own weather station. Upon request, climate sensors can also be installed directly next to the test specimen or test façades in order to record the specific microclimate at each sample location. Depending on the installation location, dew and rainwater runoff from the samples can be collected and chemically analyzed in the trace analysis laboratory.

The development of growth on the surfaces is regularly monitored visually and rated according to standardized evaluation scheme.

For a reliable assessment, a minimum exposure period of twelve months is required and an exposure period covering two climate cycles is advisable.

We recommend not only a quantitative assessment of the growth, but also a microbiological characterization of the growth, i.e. also identifying the growing microorganisms. Knowledge of the microorganisms, combined with the material parameters, provides a solid basis for optimizing the surface coating.