Importantly, as limestone is acid sensitive, it is important to use solutions that will not damage your stone and always test any product in an inconspicuous area first.
Efflorescence, in its very early stages can be removed using certain non-acidic cleaning solutions and an abrasive nylon pad, however once it becomes insoluble can be very difficult to remove. In its more advanced stages efflorescence will require specialist equipment and removal solutions.
Once the removal process is finished and the surface is completely dry, you should reseal your limestone using a long lasting penetrating sealer which greatly reduces water uptake.
Efflorescence can be removed, however it is an indication of another issue which will need to be dealt with to prevent the problem from simply recurring.
Water entry to the tiling system can be minimised by binding, waterproofing and sealing, among other options. Without water, the efflorescence cannot form.
The two key principles for minimising efflorescence are to minimise the entry of water into the tiling system, and to direct water that penetrates the tiling system to a designed outlet.
Sealing using a penetrating sealer will prevent water from being absorbed into limestone and also allow the stone to release any built up vapour. Unsealed limestone that has absorbed moisture can also result in efflorescence being deposited on the surface as the moisture evaporates.Topical coatings which block the pores should be avoided. They can trap water inside the material and make the surface dangerously slippery when wet.