Dark grout turned white

[IE00]

We had slate tiles installed in our bathroom with grey grout.

After a few days the grouting turned white. We have not sealed the floor yet because we wanted to remove the white residue off the grouting before it is sealed.

I read online that this could be down to latex leaching or efforlescence, so I cleaned the grouting with a vinegar solution but it is still white.

Any ideas on how I can get the grouting back to its original dark grey colour?

Untitled

• IE00
• 8 Mar 2015
• 1

[/img]

 

[ree]

What type (Mfr's description please) of adhesive did you use?

What was the background for the adhesive?

Was the colored grout pre-mixed or did you mix the color in?

Were the slates pre-sealed before fixing?

Was latex liquid additive used in the adhesive or the grout? If it was did you follow Mfr's instructions?