What's a tile bay forgive my ignorance?If it’s stone you should uncouple regardless, if it’s full bodied porcelain then you shouldn’t have to uncouple unless there is an issue with the screed. Uncoupling doesn't do away with the necessity of expansion joints, tile bay sizes and lengths of runs still have to be honoured and in some instances the amount of windows and colour of tile can also contribute to the limits of bays in respect to expansion. uncoupling though imo is never a bad thing.