The resin in cement is organic –which provides the fungus' spores with
nutrients. The establishment begins.
The mortar's surface binds damp and dirt which provides the fungus with even more nutrients. Fungus binds strongly to the mortar's coarse surface and is therefore hard to counteract.
Fungus spores and remains of fungus on the mortar surface enable the affections to recur constantly. The only substance that guarantees to kills all fungus affections and growth for four years is Bensaltenside.
The protection does usually last longer. The treatment involves sterilizing and disinfection.