I recently bought a house and the main shower had some grout that was chipping away and maybe even allowing water under the tiles. I figured the best way to proceed was to regrout the whole shower.
Reading some tutorials online, every one suggests removing the old grout using a grout saw and/or a utility knife. I did this (what a pain!) but there is still grout that is securely between the tiles and would take a lot more work to chip that away.
My question is, do I need to remove _all_ the old grout before applying the new grout or is removing the loose stuff and the top layer of the old stuff good enough?