Whether you are dealing with excess thinset residue left on the face of an installation or the thinset that has bonded to the back of the tile and stuck with it even after removal for a remodel project, there are a variety of ways you might remove thinset from porcelain tiles. The methods for doing so depend on the level of thinset that has adhered to the tile, and while you can remove light thinset with nothing more than a wet sponge, the thickest areas will require special consideration.
Remove smaller sections or light coatings of thinset from porcelain tiles with a wet sponge. Dampen the offending area of thinset and let the water soak into it. Wait a few minutes and repeat the process until the thinset remains a dark color. After the water has soaked through it, you can apply a little bit of pressure and the thinset will scrub right off the face with the sponge.
Repeat the same process for thicker areas of thinset on the porcelain tile, but use vinegar instead if the piece won't easily scrub off with a sponge. Dampen the thinset area as you would with water, but use straight white vinegar. Vinegar is a light acid and works well for concrete-based materials when it comes to cleanup.
Put on protective gear, including a respirator. Fill a container with muriatic acid and soak the pieces in the solution if you need to remove thinset from porcelain tiles in a demolition project. Muriatic acid is a fast-acting acid that works well against cement-based materials. Remove the pieces when they are clean of thinset and rinse them off with water.