Short answer
Saltpeter generally comes back because moisture continues to migrate through the wall. As long as the cause remains active, hygroscopic salts may reappear despite cleaning.
What cleaning does not treat
Saltpeter is neither a stone disease nor a fungus. It appears when salts carried by moisture reach the surface.
Brushing, washing, or painting can remove or hide the visible mark. They are not enough if water continues to circulate in the wall.
Causes to check
Rising damp is a common cause when the marks are located at the bottom of the wall or form a damp band.
Old water damage, infiltration, or significant condensation may also sustain the moisture. The same visible effect may therefore have several origins.
Do the marks keep coming back despite cleaning?
That is often a sign that the cause needs analysing, not just the surface.
What to do before repainting?
You first need to identify the cause and check whether the substrate is dry enough. Redoing plaster or paint too early exposes you to recurrence.
MURSAIN starts with a diagnosis, then directs you to the suitable solution depending on the building: HYGRO if rising damp is involved, air treatment, drying, or another path depending on the case.
Frequently asked questions
Does an anti-saltpeter product prevent deposits from coming back?
It may clean the surface, but it does not treat the cause if moisture continues to migrate through the wall.
Do you have to wait a long time before repainting?
The delay depends on the cause and the condition of the substrate. The diagnosis helps define the right sequence.