The biggest problem is that the usual construction is that the earthquake frame goes down either to be anchored in bedrock or with inverted "mushrooms" of concrete about 1 m 80 deep. The slab is then cast directly on the ground, anchoring into the frame. The pipework, electrical conduits etc. are placed loosely on the slab and then a 4 cm layer of damp sea sand (cheapest, but salty) is placed on top to "fix the peipes, and then the screed is cast on top of the sand. The gaps in the outside walls are filled with brickwork, but the quality of the bricks is atrocious, more like sponges than real bricks. The walls are then "plastered" with cement (often made with sea sand), not with real plaster. Damp courses are unknown, as it is believed that the slab is good enough, as it is above ground level.
Most problems, such as you describe, can occur on both sides of all outside walls, often to a height of over 1 m, and are due to rising damp from the ground, exacerbated by the hygroscopicity of the sea sand between the screed and the slab, as well as in the cement and concrete, and the porosity of the bricks. In bad cases, it can even affect interior walls where they join onto exterior walls. However, most problems with interior walls (as opposed to the inside of exterior walls) are due to the pipes in the sand leaking or excessive washing when cleaning the floors.
It is rare for rain to cause the problem, as the polymer coating in the paint will prevent ingress to the "plaster".
Been there, done that!