Hi after some advice . Just finished the shower cubicle , used a Mapei white grout and the grout goes grey and absorbs water . After a while it dries out again , but this is not normal ? I have the same tile in my other bathroom but used a cheap travis Perkins 4 trade grout and had no problems . My builder insisted on using this ( he did the refurb ) a decent quality white adhesive was used Norcros , the wall was prepared with an acrylic primer . Just cannot understand why the grout is absorbing water like this ?