use carbide blade to remove grout in small area
use rotary tool to remove grout in larger area
work slowly and stay to the center to avoid damage
Cut Away the Grout
For small areas, use a grout removal tool with a carbide blade. The blade is harder than the grout and will cut it away (Image 1).
For much larger areas, use a rotary tool (Image 2).
Make sure the bit is the right size for the space between the tiles, and adjust the bit to the proper depth.
Work slowly (Image 3). If the dust is a different color than the grout, you may be hitting your tile -- stay to the center to avoid damage.