Damp patches in bedroom after plastering hallway

The window reveal will be a cold spot where naturally humidity will settle but with ventilation will dissipate. The wall where the moisture is settling is a cold wall (is it an external?) and again humidity is drawn to the coldest surfaces. If you have just had a lot of plastering done that involves water and thus moisture is released when curing then this humidty created has just highlighted the coldest surfaces. The chimney breast could be suffering with another problem altogether - hygroscopic (moisture absorbing) salt contamination from when it was used to burn wood/coal etc ( depends on the age of the property??!!) Conclusion Give it time for the moisture to naturally dry and disappear and if it does not then contact a specialist damp company to come assess and quote Many Thanks Steve- Dynamic Property Care UK