Two years ago I covered the walls of the room with drywall. Started noticing signs of dampness, lagging wallpaper, black traces of mold. When I opened the sheet, the plasterboard found abundant moisture on the wall. The old plaster is completely wet, on the profiles below hanging water droplets. What is it – it is possible to sweat and how to deal with it now? The house is old, one-storey, 60 cm thick stone wall. Behind the wall is another apartment.
There are a lot of reasons, and the drywall has nothing to do with it. The house is one-story, there is poor waterproofing, dampness is coming from the basement.
What could be the problem:
The floor slab is not waterproofed. Problems with the roof, the wall gets damp at the top, treatment, repair the roof. Poor ventilation in the room, installed new double-glazed windows on the exit got a "thermos". House is not insulated, in the cold season, the dew point moves into the interior. There is a need for external insulation.
The only thing confusing, you write that behind the wall of another apartment, it is not clear whether only this wall adjacent to the apartment, or all the walls in the room gets damp.
Not enough heating, it is damp and cold in the room, this too can be a reason.
If in general and plasterboard is not waterproof, you need to replace it, dry the wall, mold deeply penetrates into the plaster (you wrote about the old), plaster may have to remove completely and treat the walls with products that destroy mold, for example not bad, used in living quarters "Quelyd".
And then to deal with the cause and eliminate it (see above, waterproofing, roofing, etc.)
The reason for the formation of damp under the sheet plasterboard most likely – lack of ventilation between the plasterboard and the wall, ie it was in a vacuum, and to eliminate this defect, you need to arrange ventilation grates are approximately the same as they do on the floor, in the corners below and above.
It does not take into account the gap in the outer wall between the apartments and plasterboard upholstery – a strip width of 50-100 mm, it is the main reason for the formation of all the problems.
Therefore, the second way to eliminate this problem could be to insulate this section of the wall from the floor to the ceiling, but it is unlikely to eliminate the problem, because the cold bridges will still remain (technically difficult to solve the problem with thermal bridges in secondary housing – easier to solve in the new construction) and especially if their area is large, and probably the floor and ceiling will also have to insulate – they also come in contact possibly through insulation and the outside air, the ceiling through the attic and the floor through the basement – so the best solution – it ventilates
Mildew is very difficult to eliminate. It is better to dismantle your construction and plaster it again – it will be cheaper.
The first reason is excessive humidity in the room. 40-60% is considered normal for humans. Anything above this value is harmful not only to the occupants, but also to the structures themselves. You can measure the humidity with a hygrometer. If the humidity is within normal limits, this is not the cause.
Not only humidity, uneven heating, but even the presence of an aquarium or a large number of potted flowers in the room can affect the appearance of mold.
What you need to do first is to ensure regular ventilation of the room, previously moving the furniture away from the problematic walls.
In your case, you will have to dismantle the drywall, remove mold with a stiff brush, clean the surface and then, treat the wall with a special antimold agent. You can use Domestos. Or you can buy the necessary products in a construction store.
A cleaned and treated wall must be dried thoroughly! A blowtorch can be used (just be careful not to start a fire) or a construction dryer.
The next step is to treat the wall with antifungal composition, antiseptic, or other means – now there is a very wide choice in stores.
If the house has an unventilated basement, then that's where the problem is. That's probably where the moisture is coming from.
When you covered the wall with plaster, without proper insulation and waterproofing at the bottom, near the floor, there was a situation of accumulation of moisture and condensation. There is no escape of moisture, no ventilation, hence all the artifacts. It is possible that there is no basement or cellar, but the wall itself is not waterproofed from the foundation, and it is the foundation that is pulling the moisture. The only thing to fight is to open up the floors, look at what is below, whether there are any pipes, which is also possible, and waterproof and insulate.