We had our kitchen remodeled last year and removed/saved the old tile. We are now doing a bathroom and want to reuse the tile. How do I remove old grout from the back of tile so I can reuse the tile?

Are you referring to the adhesive that was used to hold it in place if so is it a cement type material (thinset) or a mastic type adhesive. I believe there are some chemicals that might break down the mastic but the thinset would be a real pain to remove unless someone else has heard of some other way the only way I know to remove thinset is scrape,sand or grind let me know exactly what your trying to remove and we will see what we can figure out GOOD LUCK ,AC

Carbide rasp on the fein multimaster. C. & E. FEIN GmbH - Der FEIN MULTIMASTER

Look at the videos on the website.

The tool oscillates.

Great looking tool looks like it would do the job. I think I might just add that to my christmas list

This is just a general rule of thumb, don't try to save old tiles. The thinset is going to be a big problem properly removing it and you will break many tiles. This will limit the possible reuse of tiles to only smaller jobs and the tile itself isn't horribly expensive to begin with. Remember, time is money even for the DIYers.

You could use a large notch trowel (greater than the largest thickness of old mortar) and press tiles into bed according to thickness of thinset the back. I do this when using inconsistently thick material, such as slate.