Robbo - where is the damp patch? What type of apartment have you got? ...... make it easier for someone to identify a similar issue if they have had it.
In my 3 bed in Jardin 4, i was getting damp in the main bedroom wardrobe at floor level.
Fixed it by taking out the bath, taking up the floor, and connecting the plughole drain with pipes to the main drain - the bath/shower water was going down the plughole onto the floor and it was just spreading outwards by the easiest route which was towards the main bedroom ...........
Had a walk in shower put in in place of the bath ........... no problems since (2 years ago), wall repainted once dried out.
p.s. was going to have the shower put in anyway, as i just thought it was splash from the existing bath/shower going on the floor and spreading