Anything mold on the walls in the house that breathes. In fact, the problem is all there: if you have already ruled out that it is rising damp that can be remedied with a technological intervention, the presence of mold smelly on walls it is always an indication of poor ventilation of the environment, when not of breakdowns or structural defects in the most serious cases.
The first thing to do is to identify the cause or causes of the mold. If at the origin of the stains on the walls there is a water leak from a pipe, all that remains is to crack the Wall and replace or fix the faulty or damaged part. If, on the other hand, the origin of the mold it is a thermal bridge, that is an uninsulated point of the structure where a passage of humidity is created, the (demanding) solution is a thermal coat or in any case an external insulating barrier.
However, beware of excess insulation and the quality of insulating materials, which paradoxically may be the cause of the formation of molds on the walls even in new buildings and in any case they do not contribute to living comfort. Waterproof insulation and vapor barriers seal the house favoring the formation of condensation. Conversely, porous building materials (stone, brick, wood ...) and breathable insulators (cork, wood fiber, sheep's wool ...) allow the exchange of air and keep the house well ventilated and dry, essential conditions to avoid the formation of mold, without losing heat.
Beware of the catch when it comes to thermal insulation to save on heating. The insulating coats obtained by applying on walls external synthetic insulating panels and plastic coatings are effective in containing internal heat, but equally dissipative towards solar radiation (they obstruct the sun's rays) and illogical not to say unhealthy from a physical point of view because they prevent the building from 'breathing '. With the humidity that does not find an outlet to the outside, it is obvious that condensation forms inside and hence the mold on the walls.
If the house is 'sealed' by non-breathable insulating materials, the air exchange that takes away the moisture and prevents mold on the walls it just depends on how long the windows are open. In this way, however, all the heat that was thought to be saved by providing good insulation is wasted. It is a vicious circle that must warn against excess insulation and synthetic sealing thermal coats.
An insulating thermal coat should be breathable and it is not true that this feature makes it less effective than synthetic competitors. The passage of air in the porous insulators (which are almost always natural materials, therefore also more ecological) is so slow that it does not cause heat loss, if anything it helps expel polluted air and contributes to overall living comfort. The superficial envelope of the house must act as a 'skin' that transpires and this is actually the only sure way to avoid the problem of mold on the walls.
You can also read our article: Mold on the walls: natural remedies