Grout problem

[Morton]

A few years ago we had a small extension and where the old bathroom floor meets the new build, it is slightly higher. Therefore, there is a small tiled slope. My problem is where the grout line between the slope and the new flat floor meets - it breaks up after about a year and I have to rake it out and re grout. There is no settlement or anything like that but it crumbles/shrinks? Anything I can do to prevent this next time I rake out and grout? It doesn't happen anywhere else, only along this line.

[Rookery]

A movement joint should have been installed where the old meets the new. You might be better off raking out the grout and siliconing this joint.