Before masking the smell, you need to find what keeps it going. Otherwise, the issue quickly returns.

Airing rooms is important, however damp at the bottom of a wall can reveal more than condensation.

Saltpetre cannot be solved only with surface cleaning. First, you need to understand why the wall stays damp.

Repainting without understanding the cause may hide the issue for a few weeks, then damp returns.

Before choosing a solution, it is useful to identify the likely source of damp and avoid rushed decisions.