I am a little late coming to this blog, but I know a lot of people are suffering from damp here in Spain and have read through the replies, noting some are a little off the mark in terms of good advice.
Most of the damp problems here in Spain are rising damp due to the method of build, you cannot stop the problem by placing a membrane, painted on or otherwise, on the wall, you are simply burying the problem, To place a membrane is like putting a poultice on a wound, it will draw the damp up the wall, which can cause structural problems, especially in old walls. the damp must be stopped at source. Further more, Spain is high in salts which is drawn up with the damp, breaking out on the surface about .8 of a meter high, it shows as a white powdery substance, this will eventually destroy the plaster work. Many people will approach this problem by using the same method as the UK, this is incorrect as the construction is different here in Spain.
Damp control is really not a DIY undertaking, also wiping spores away with bleach is only removing the symptom, it is not a cure, spores are also airborne and in fabrics which is bad for your health and home. You can see more on www.123bmt.com
Hope this helps. Kind regards Brian Tones. Architect.