Mike,

Hammer and bar. Once you've broken through you can pry it out in
chunks. But, if the curb or dam is removed first you can tap the bar
under the mortar bed and tile, and pry it up. it will crack. Most
mortar beds in shower basins is made of a sand and cement mixture minus
lime.

Mike wrote:
Thanks, Roger. The shower is actually on the second floor, and the
floor tiles are imbedded in a mortar base. We've pulled off some of the
wall tiles along the floor, and we can see the degraded mortar, a wire
mesh support and behind that, the vinyl liner.

Given that, suggestions for removal of the floor, anyone?