Thanks all for your comments. Yes, it's an oscillating tool. As suggested by cam_low I think part of the problem is that his grout removal blade is too wide for the joints. He's worried about chipping the tiles so isn't going deep enough. Don't know why he doesn't get a thinner blade.
Getting a bathroom regrouted, bit concerned tiler has only taken the top layer of old grout out. Thought at least 3mm of tile sides needed exposing for the new grout to adhere? Please let me know your opinions.
