Rising damp occurs when groundwater soaks into a building’s walls and moves upward. It carries salts such as sulphates, nitrates, and chlorides, which deposit on surfaces as efflorescence. This white powdery residue is often visible on brick, stone, or stucco. Damp marks commonly appear up to a metre above the floor. https://www.damp-solutions.com/types-of-damp/rising-damp/