This sounds like you have an efflorescence problem...try using lithofin cement away it should help.....heres a description of what it is....
Efflorescence. A salt deposit visible on the grout or on the tile edge also becomes an unsatisfactory situation. What is efflorescence? Efflorescence results from a soluble salt present in your mortar setting bed, in your cementitous grout and in concrete slabs. It remains fairly inert unless moisture is present, in which case the salt moves to the surface where it dries into a white, crumbly powder.
Where does the water come from? It may be available in the concrete substrate or in the cement mortar (where too much mixing water has been used). The water may come from the cementitous grout itself, particularly if excess mixing water was used - a situation which also results in voids in the grout that allow easy passage of water from the concrete or mortar mix. Elimination of efflorescence is achieved by some of the following methods. When installing over an on-grade slab, a vapor retarder should be in place beneath the slab. Use a meter to check moisture emissions. Other preventive measures include allowing your setting bed to dry (and cure), using proper mixing techniques, installing dense grout joints, not using excessive water in dressing joints, and using kraft paper for curing.
