Terry, this is pretty tough to do without breaking the tile. How many do you need to remove the thin set from? A hammer and chisel with some well placed taps should knock it off, but it is going to be tough. There are more powerful power tools that will do the job, but probably will not leave the tile intact.
Once this stuff dries it is pretty much impossible to remove. You may be able to grind it off however. If you have several you could make a jig with some scrap wood line the bottom with a carpet scrap set tile into it and using a small hand grinder remove the offending material. It will take some time but you can be successful with this method.
can i get an attachment for my dremel or do i need a special grinder? dan i have about 4 to 6 to do.i am able to get them up off the floor with lots of patience, dremel tool and pry bar (slowly) but the denshield and morter is stuck to the back.
Shame you cannot purchase new matching tiles. As far as Dremel tool, if they make a grinder attachment I assume they do that would be fine. If not you can always rent a hand grinder and purchase a grinding disk that will remove this material. Forget about the oscillating tools that they sell. They are ok for cutting into wall board, or grinding grout, but forget about removal of something as hard as the material on back of a tile. You will go through way to many blades to get the job done.
a basic electric sander and patience
im finding i have more patience than i ever thought possible doing this project, and the idea of matching tiles is not out altogether just trying to keep it all the same if possible. thanks so much for the ideas and the info really appreciate your time.
I'd go with the 4" right angle grinder with a basic multi purpose "cup stone"...building a small wood frame to "hold" the tile will help.
The Rockwell tool would work nicely!!
I hav had to do this many times. I use a 4" grinder with a diamond blade. This s dusty, but it works every time. http://www.cwremodelcontractor.com/tile-installation.html
The dust is a pain...If you can do this outside so much the better...use a dust mask