Luigi’s Answer: Under certain circumstances, a white powder can form on grout, especially on floor tiles. This is a natural phenomenon known as efflorescence. It is due to soluble salts rising to the surface of a cement based product. When they dry out on the surface, the remaining salts appear white and powdery.
What causes the problem?
There are many examples where Effloresence appears in some situations but does not appear in others, under the exact same circumstance. It is quite a mystery in the tiling and brick-work world. We do know that it is a reaction when Portland cement is present, and that 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 simply showing the effects of the soluble salts coming from beneath the tiles. It is not due to substandard tiles, adhesives, or grout; and generally, (other than aesthetics) there is nothing to worry about.
Luigi Suggests:
The only real solution is to brush the grout with a stiff bristled brush and vacuum away. Repeat this from time to time, and eventually, it will generally stop recurring. You can use specialist products such as Aquamix Eff- Ex.
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