Why is the plaster of my new house (- 5 years old) already covered with blackish streaks? How to remove them?
The black marks on a plaster usually come from atmospheric pollution, on the facades of facades exposed to rain. On a wall facing north, it may be moss. In the first case, try a cleaning with a detergent using a high-pressure cleaner whose nozzle will be about thirty centimeters away from the wall. In the second case, use a commercial antifoam. Do not use bleach, even very diluted (as seen on most forums), chlorine being dangerous for the environment and for yourself.
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