The problem of mold stains is at the top of the ranking of disputes between sellers and buyers in the real estate sector, to the point that the definition of mold damage. But what do the mold stains on the walls? Excluding the possibility of leaks from pipes or rising damp, there is always a problem of isolation due to an error in the design or construction of the building that causes the passage and accumulation of moisture in some points of the structure, hence the formation of foul-smelling molds on the walls.
The problem of mold stains it may be due to the total lack of insulation in the walls, but since it has begun to pay a minimum of attention to energy performance of buildings the cause is more likely to be insidious thermal bridge, that is, an area or a point where there is no insulation between the internal and external part of the wall, resulting in the passage (hence the definition of bridge) of humidity from outside to inside.
You know the stained facades of dark mold of some buildings? Here, that's a thermal bridge due to the total lack of isolation inside the wall. When the mold stains are concentrated in the corners and joints (see photo) means that theisolation between beams and pillars: the walls are perhaps well insulated, but the load-bearing structure has been forgotten and since reinforced concrete is a good conductor of moisture, pillars and beams become thermal bridges.
The problem is aggravated by climatic factors: strong thermal excursions, low temperatures, rainfall and low insolation cause the proliferation of mold stains in the absence of adequate insulation. Typically the damage of the thermal bridges they are more evident in cold climate areas and in the winter season, when the difference in temperature between outside and inside is higher. As with the moss on trees, the favorite part of humidity and mold it is the one facing north because it is not heated by the sun.
The situation is delicate and the damage of the thermal bridges it is always twofold: on the one hand there is the thermal dispersion of heat that drives up heating costs (even over 30% in some cases), on the other there is an even more serious problem related to health. There mold, of different types, it is an active colony of fungal microorganisms and can seriously compromise the livability of an environment even for those who do not have particular allergies. Bad smell is the least serious aspect.
Unfortunately when the mold stains on the walls and the bad smell arrives it means that the problem has existed for some time and scraping the plaster (which is not recommended) is useless. Hyper-chemical opaque and sealant paints are also of little or nothing, which if anything further worsen the health of the environment. The only possible remedy is a corrective one and always quite expensive.
Before any intervention, however, it is necessary to understand the true origin of the problem, also to completely exclude the presence of leaky pipes or other types of faults. In this operation, the infrared thermography, which allows you to photograph the thermal situation of the entire building or the portion of it where the mold stains are highlighted. There IR thermography it is used by insiders to plan the least invasive interventions possible, but it can also be used by individuals to check the state of health before a purchase or to document the problem to the seller who had hidden it.
Once it is discovered that the mold stains depend on the lack of insulation in the walls or from structural thermal bridges the remedy is almost always only one insulating coat, which consists in applying a panel of insulating material covered with a plaster, reinforced with a reinforcement and completed by a finishing layer, to the external face of the wall. It can be done with different insulating materials: blond cork (not toasted, which is another thing) is one of the best because it is resistant and breathable, as well as ecological.
The trouble is that the insulating coat it is an expensive intervention and if it is a condominium, everyone must agree. Two tips to avoid the mold damage: if you are building a new house, make sure it is well insulated and that the designer and even more so the construction manager are well aware of the possible problems. Often the mold damage was born on site due to haste, superficiality and poor implementation. The attention of the construction manager is essential.
If, on the other hand, you are about to buy a property already built, ask the seller for all possible insurances, possibly including one IR thermography. Don't trust the newly whitewashed rooms that are shown to you in the height of summer (when the thermal bridges are less obvious). If you have legitimate suspicions, give up the purchase and look elsewhere, given the stakes it is not worth the risk.