is it dampness?

The black spots are mould caused by a high humidity - ventilation and a dehumidifier might help.

Ideally there should be a vent fan in a bathroom to keep the dampness down. Bathroom fans with a humidistat are available.

You can buy a cheap but reliable greenhouse humidity meter from a garden centre for about £5 - then you know what progress you're making and when to stop worrying.

The black spots (mould) will keep coming back while the walls remain damp from condensation.

http://www.scotland.gov.uk/Publications/2005/05/10103020/30217

http://www.diydata.com/problem/condensation/condensation.php

http://healthandenergy.com/mold_prevention.htm

Good luck...

Peccavi
January 2010