removal of existing thinset?

Question- do you have to remove existing thinset mortar before re-tiling with ceramic tile. If so, any good solutions for getting up the thinset that is stuck to a concrete slab. Can a anti cracking membrane be applied directly over the existing thinset that is on the concrete slab and then tile over that? Any responses would be greatly appreciated. Thanks

Your tile substrate should be smooth and plane. To install a membrane over an irregular surface in an attempt to shortcut any other preparation wouldn't be adviseable.

Once the surface is smooth then the membrane can be applied.

The only other suggestion would be to use a Self Levelling Compound but don't forget the related primer.

This is not to say you absilutely cannot go directly over the existing thinset surface, it just depends on how rough that surface is now. The surface can be sanded mechanically using a floor machine or a floor grinder.

Thank you for the tip. Grinding seems to be the method of choice, and with the time saved grinding, it'll make the cleaning up and vacuuming seem easier!

Use drop cloths to curtain off the area you're working in, and you cut WAY down on the clean up. If you're tiling the entire room, close off the doorways. If a small area of the room, use plastic drop cloths to tent off the immediate area. Use 1x4's, cut about 6" longer than the ceiling height, and spring them into place to hold the drop cloth against the ceiling