ᐅ Black circular spots on the exterior wall

Created on: 21 Nov 2014 20:09
J
JohnnyChicago
J
JohnnyChicago
21 Nov 2014 20:09
Hello

Some technical details (I’m not a professional, just copying this from the building plan).

Facade with 16 cm (6 inches) insulation, Lambda value 0.032 W/mK, hydrophobic base coat, silicone-based facade plaster with 2 mm (0.08 inches) grain size
Bisotherm 30 cm (12 inches) exterior wall
Not a low-energy house, meaning no mechanical ventilation and no Blower Door test was performed.
Regular manual ventilation (very thorough)
Indoor climate feels very comfortable (I haven’t installed a hygrometer)
New build from 2012

Today (2°C (36°F) outside temperature at night, dry weather but heavy fog) in the morning I noticed two circular spots on the facade, each about 20 cm (8 inches) in diameter.

The spots look like crop circles, meaning nothing in the center and the outer edge consists of small black dots that cannot be easily removed.

The facade color is a light yellow shade.

What could this be?

Thanks in advance for your effort and responses