Rising damp describes ground moisture moving upwards through porous masonry where an effective barrier is absent or defective. Condensation forms when moisture-laden air meets a surface that is cold enough for water to collect. Both can damage finishes, and a property can have more than one moisture source.
Patterns that may be relevant
Low-level moisture and salt-contaminated plaster can be consistent with rising damp, but bridging, leaks and hygroscopic salts can produce a similar pattern. Surface mould behind furniture, around cold corners or in poorly ventilated rooms is often associated with condensation, but rainwater entry and plumbing leaks should still be ruled out.
Why a meter reading is not enough
Handheld meters are useful for comparing patterns, but they can respond to salts and materials as well as moisture. A useful inspection also considers external ground levels, rainwater goods, ventilation, heating, room use, plumbing and the construction of the wall or floor.
Avoid selecting a chemical damp-proof course or ventilation system from photographs alone. The remedy should follow the evidence found at the property.