Rising Damp is normally found in older properties where the lack of any efficient damp proof course allows moisture from the ground to rise up through the brickwork by capillary action. Most damp proof courses have a limited life, 30-50 years being the norm.
The visible signs of rising damp include discolouration and staining above skirting level, rotted skirtings, and contaminated wall plaster.
The only satisfactory solution is to remove all contaminated plaster. Install a new damp course and carry out specialist replastering. Silicone damp courses have stood the test of time and are totally efficient.