Is this mould, humidity or rising damp?
Unfortunately there is sometimes some confusion about framing the problem at hand. At BETA we have a solution for all of these problems though the first step would be to properly understand the problem.
(1) Mould and condensation marks (pictured above) are generally caused by warm humid air causing water condensation on cold walls and ceilings. BETA have the best solution on the market for this type of problem. We recommend a pre-treatment of BETA Fungiwash and two coats of Betamatt +Antimould in the colour of your choice. This is a long term, cost effective, and most of all easily applied solution.
(2) We consider humidity to be a large amount of water in the air, this can be caused by poor ventilation and/or rising damp. An easy way of increasing ventilation would be to cut new ventilator holes or clear out existing ones from anything that might be blocking them (birds nests, plaster, etc..)
Humidity is a leading cause of mould (in case of mould see point (1)) though it's causes require a different solution. In the case of rising damp or damp walls it would be best to find the source of the water source.
It can also be caused by leaking water or drainage pipes, an experienced plumber would be able to help you fix the leak. Once the walls have been allowed to dry you can refinish the wall using Betamatt +Antimould.
Alternatively this could be due to rising damp from beneath the building. Once again BETA offers another foolproof solution in the form of Marmox boards. Marmox boards are made from an extruded foam centre with a coating of impermeable cement mortar on each side. They can be fixed on to the wall using Nylon Dowels and treated to create a seamless impermeable lining. The end result is a level, finely finished wall with no signs of rising damp. Come visit us at BETA Centre in order to get a detailed explanation on how the boards should be installed.