We live in a 300+ year old townhouse in Spain and as a result of our house being built into a mountain our ground floor back walls are underground. I have recently noticed the books on the bookshelf on the back wall being damp and a bit mouldy and when I removed them I found that the paint is coming off the walls. There are no black marks but the walls feel cold and damp and there is white fluffy crystalised stuff on the wall. We do have paint flaking off our walls in various places and were told that this is to do with lime in the walls.
In our bathroom, again a room with one underground wall, there are black and dark green/grey spots on the walls which I have wiped off with bleach but they have come back. Is it just a case of ventilating these rooms more? Summer is here (27-30 degrees and it is dry heat) or should I use a dehumidifier or do I need to do something more drastic? I'm a bit clueless!
Thanks for your help,