grey grout with white patches

[j77drs]

i have grey grout in my bathroom and overtime there are white patches appearing when dry, if the grout is wet it looks perfect

any ideas why this is doing this and why ?

can i remove this ?

the grout used was a ready mixed one

 

[tictic]

Ready mixed grout is not the...best...off gear to use...it will eventually break down as its not as strong as powered grout...and doesn't have the barriers to stop break down...

Also can be efflorescence...salt in it...just what happens in brick mortar..white patches in the cement work you see on houses..(when dry day you will see it,but when it rains,you can't see it)..

You should be able to scrape/rake the grout out,there are small hand held devices that can do this..dremmels ect.....

 

[j77drs]

is there a cleaner to use to get rid of the white ?