My Grout cracking

if your bathroom is upstairs then the reason the grout is cracking is due to movement in the tiles, the floor itself or the building check for any movement in the tiles you can do this by applying pressure to areas such as corners of tiles or along one side at a time. if there is movement in the floor then you'll struggle to get around this without taking up the tiles and boarding underneath prior to tilling via cement board 6mm-12mm thick to reduce movement to nill. if you are downstairs and is tiled onto a solid floor then there would be loose tiles where the adhesive hasn't grabbed very well and has let the tile become lose thus causing the grout line to crack. if. this is the case then you have movement in the tiles then they would need to be relaid. if there is no movement in the floor then try a very flexible grout with added polymers in it, I know toppstiles do a great selection of flexible grouts but they can get pricey. Edit: regarding wall tiles there must be movement in the tiles then. Best bet is to re-install tile(s) all around where the crack is if you can't find the cause and 're apply with fresh adhesive and grout.

where are the tiles located and are the walls solid or stud walls? obviously theres some movement causing the cracking.