Grout is a cement based product that can be effected by efflorescence. A whitish film that forms when the salts and minerals from water rise to the surface and dry on top creating an ugly looking appearance. For the most part, It looks way worse than it actually is. Whenever you hear of someone say that they grouted and the next day, the grout turned white...there is a good chance that have been hit with efflorescence. That is not always the case but is possible if the grout work was done before the thinset had time to dry completely trapping excess water and moisture. You can avoid alot of headache by waiting 24 hours after the tile was set before grouting. Some jobs are on a tight schedule and may need to be grouted sooner. Ceramictilepro recommends using a rapid set type of thinset which can be grouted 2 hours after the tile has been set.
Efflorescence can be removed with a sulfamic acid. It is usually recommended to wait 10 days after the tile has been installed to make sure all the moisture has had a chance to escape before starting this process. A solution of sulfamic acid and water is applied directly to the grout using a nylon scrub brush. Agitate with brush and rinse with clean water after a few minutes. This is not an exact science and you may want to experiment in a area where it will be less visible. Sometimes you may need a stronger solution mix and may even sit for a longer period of time. Just make sure to rinse completely with clean water. Just like all acids, keep from touching any metal objects as they will become etched and lose their protective finish which can result in rust. Don't forget to wear safety glasses and rubber gloves!
You will need to wait until all the water has dried up before you will know if the efflorescence was removed. Most of the time it works pretty good and you will have the original grout color super clean and ready for some grout sealer. If the grout was unchanged, chance are that is was either not treated correctly with the sulfamic acid or the grout itself had a bad color mix. This very rarely happens and can be fixed if you are uncomfortable with the color using a color sealant.
