Just spoke to tile giant (where we got the grout) they said that it's down to it not being mixed properly and that the 2 options are to rake out and regrout or go for the grout reviver pen.
Spoke to my builder and he said rake out isn't an option so go for the pens, I thought great so ordered them and now he's saying that he doesn't know why he should be paying 🤦
Spoke to my builder and he said rake out isn't an option so go for the pens, I thought great so ordered them and now he's saying that he doesn't know why he should be paying 🤦