had exactly the same problem witht the white 3 times also and will never use again,,also had the same comments back from mapei regarding mixing,was there contamination etc..at the end of the day this is clearly a more widespread problem than just a faulty batch or incorrect mix and wold be interesting to see what mapei say as clearly patchy or greyish grout meant to be white can ruin a finished job. all mapeis products iv used are excellent apart from this it would be nice to se them actually aknowledge there is a problem