Revisions log for Answer #1204
This is the answer to the question Why is there dampness on a wall covered with drywall? How to fix it?
Revision 1
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.