Orijinal gönderinin sahibi: pollytintop ,
remove the plaster and then treat the concrete beneath....we had a stone (as in rock) wall that had water seep through the cement onto our plasterwork. It created a chemical/salt that leeched through again and destroyed our nice new plaster! You may have to look at drainage beneath that wall and guttering/joining to find the source of the concrete decay. Then you can sort the plaster.