Too much humidity in a cellar is a problem, not only because you can't put anything in it, but also because there is a great risk of humidity rising in the house.
Investigate the causes of humidity in the cellar
A basement without ventilation is often humid, and leaks from collectors, pipe joints, or infiltration of water from the outside can increase this ambient humidity. A first operation will therefore consist in eliminating these causes, by plugging up any leaks, even minor, and draining the water outside.
Clean the saltpetre
If possible, ventilations should be created to make the cellar less humid before cleaning. To get rid of the saltpetre caused by this ambient humidity, you must first remove it by vigorously brushing the affected areas, then apply a 10% solution of hydrochloric acid. Masks, gloves and special clothing are essential for this operation, then anti-saltpetre will be applied to the surfaces thus treated, which will attack the nitrifying bacteria and harden the wall.
Combat the ambient humidity in the cellar
A white anti-humidity paint, spread with a roller, will form a waterproof screen against humidity. It will not blister and prevent infiltration and mold. There are also water repellent treatments that can be injected into the walls to dry them out. Finally, it is possible to install moisture absorbers, whose calcium chloride crystals absorb the water contained in the ambient air.