Efflorescence often manifests itself in the cement joints of new brickwork. Numerous studies have been made around the world to try to determine why it can appear on some installations and not on some seemingly identical ones. The only things that we do know are that it happens when Portland Cement is present and there is no real solution for it. Efflorescence does clear up over time unless there is an ongoing issue with rising damp from the substrate. It is defined as the 'migration of soluble salts.'
This is not due to substandard tiles, adhesives, or grout; and generally there is nothing to worry about.
Called 'efflorescence,' this white stain is simply the residue of salts on the surface of the tile. It is due to the migration of soluble salts that are present in the cement based substrate. This can be the concrete, the mortar bed, tile adhesive, or grout.
These rise to the surface and as it dries, an annoying white powder remains on the surface of the unglazed tile
The only real solution is to brush the grout with a stiff bristled brush and vacuum away.
Repeat this from time to time and generally, it should eventually stop recurring.
Some people advocate brushing the salts away and then applying a penetrating tile sealer. While these are great products, and are worth using because they will keep your grout and tile clean and seal out dirt, these products generally won't stop efflorescence.
In most cases, Sealers Choice penetrating sealer applied with a lambswool applicator will help as it works by allowing vapour to transfer through to the surface, but not moisture. It allows the tile to 'breathe' and can reduce the problem, although it is not guaranteed to always work, especially in outdoor areas.
You can also wash with a 50/50 mix of water and phosphoric acid. Leave the solution on the tiles for two minutes, then thoroughly wash off with clean water.
Always take care with stone (marble, granite, and sandstone) and acid sensitive products. Check with Beaumont Tiles first and test in an inconspicuous area.