Hi
I am planning on re-tiling an existing shower. Do I have to remove old existing tile, or can I successfully re-tile over it?

Hi
You can tile over the existing shower tiles but you will have a couple of problems associated with this operation:
-If you decide to do it, first make sure that the old surface is perfectly clean, better yet, first clean it and then scratch the surface with the grinding wheel.
-Since “Mastic “is not commonly available here, you will use “Thinset” to glue the new tile with, use some acrylic additive to improve its bonding quality.
-Don’t use white “thinset” white “pegazulejo”
-What about the plumbing shower valves and the floor drain? – are you going to move it to accommodate for a new tile and glue thickness?
-What about the trim tile?
If you consider all of the above, it may just be easier to remove the old tile.
Adam

If your tile is stuck on the wall really firmly and your walls are nice and level/plumb/square then you can tile right over top..... but this may make your room look smaller so it maybe in your best interest to take the old tile off the walls if it's not too much trouble. If your walls are a mess when the tiles come off just rip off the dry wall/plaster board and replace with a new piece - or if you have brick walls be sure to give the wall a quick skim.

If your walls are drywall just cut the drywall and remove it instead of chipping the tiles off.... easy!