Algae, moss and dirt on paving and façades — causes and prevention

Why do paving and façades turn green in the first place? And can that be stopped for good, instead of being washed off again every few years? A look at the causes — and at what really helps.

Why does the growth appear at all?

Algae, moss and lichen need one thing above all: lasting damp. Surfaces that rarely see the sun — under trees, on the north side of a building, in narrow courtyards — dry off more slowly after rain and therefore offer ideal conditions. Porous or rough surfaces (many concrete pavers, untreated natural stone) encourage the growth further, because moisture and organic material lodge in the structure.

The most common causes at a glance

• Too little sunlight because of trees, shrubs or shade from the building
• Not enough fall, so that water sits on the surface instead of running off
• Leaves and organic material that are left lying and then act as a breeding ground
• Leaking or blocked gutters that send water running down one particular spot on the façade

What helps against regrowth in the long run

In summary

In shady, damp spots there is hardly any way to prevent algae and moss altogether — but with regular care and the right preventive measures you can considerably stretch out the intervals at which a thorough clean becomes necessary.

How Zamsa helps

Prevention lengthens the gap between two cleans, but it does not replace them. Once a surface has become overgrown, only stone cleaning will bring it back to its original state — and from there the measures above start working again.