Mould is often a sign that a building is not being ventilated enough and a sure sign that the area effected has excess moisture, the following photographs indicate the damage that can happen if moisture goes unchecked.

This is a ceiling above a window.

These blinds are being attacked by mould due to moisture and the lack of ventilation

Even across the top of the window mould is starting to effect the metal frame of the window blind and the plastic casing of the window.

Mould not only looks unsightly but it is also damaging, over time it will cause plaster to fail, wood to spoil and stain paintwork and plastics. Anti fungal paint and solutions can be applied but this will just mask the effects and overtime it will return.

Good ventilation is the answer, when the mould has been treated and a source of ventilation has been employed the mould will not return.