How do I clean backsplash tiles to reuse them?
For porcelain and ceramic tiles, a weak vinegar solution will often loosen mastic (and/or grout) to the point that it can be scraped off pretty easily. Do not use this on a limestone tile. Other natural materials might necessitate a test with a broken tile, just to check. If you see bubbles from anything other than the mastic, don't use vinegar.