Grout turning black after one use

[Billybuspass]

Hi
I have just had my wet room tiled and after one use the cream coloured grout has gone black in random places grout compound has a mushy consistency when raked. Its in a few places. Anyone any ideas as to why its happened or a way to remedy it ?? Tiler said he doesn’t know why it’s happened but we need to find a solution to fix it. See below.

 

[Dave]

Can’t view the pic for some reason. How long has the grouting been done and time between grouting and using shower.

 

[Kastar UK]

Dont know why number of reasons , remedy is to rake out and redo

 

[Billybuspass]

Can’t view the pic for some reason. How long has the grouting been done and time between grouting and using shower.

Original grout was down 2 weeks and shower wasn’t used and parts had turned black he came back and scraped it out on the Tuesday last week and I used the shower on the Saturday.

 

[Billybuspass]

Dont know why number of reasons , remedy is to rake out and redo

It’s been raked out once mate waited 3 days and back to square 1 when shower used

 

[Dave]

Original grout was down 2 weeks and shower wasn’t used and parts had turned black he came back and scraped it out on the Tuesday last week and I used the shower on the Saturday.

What grout manufacturer is it