There are a few possibilities. You can dissolve the salt efflorescence or remove it. When dissolving the salt efflorescence, there is always the danger that the dissolved substances will penetrate the masonry or the stone again. It is better to remove the salt efflorescence.
With the vacuum blasting method from systeco, this can be done easily and in a very environmentally friendly way. The efflorescence is completely removed from the surface. Saltpetre can also be easily removed from natural stone with vacuum blasting.