There are two ways to go about removing grout: with an electric-powered tool, or with a manual tool and a lot of determination. We’ll go over both methods below.
Removing Grout Manually
If you’d rather not purchase a power tool, the pointed metal tip of a traditional, lever-type can opener (also called a church key opener) works just as well, albeit with more time and effort.
Draw the point repeatedly along the joint to scrape out the hardened grout. If the tool becomes dull, clamp it in a vise and resharpen the tip with a file.
Alternatively, you can fasten a 6d (2-inch) finishing nail to a short wood dowel for a handy DIY grout-removing tool. Bore a small pilot hole, about an inch from the end of the dowel, then use a hammer to drive the nail through the hole.
Hold the dowel up to the wall and place the nail point in a joint between the tiles. Use short, downward strokes to scratch out the old grout. If the nail point becomes dull, sharpen it with a metal file.
Removing Grout with a Power Tool
The advantage of using a rotary tool or oscillating multi-tool for this job is speed. Rather than possibly taking a few days to complete the project, the entire project can take just a few hours. The disadvantage is that the tool may be too powerful—you might end up chewing through your tile in addition to the grout if you’re not careful.
To use a power tool, fit it with a blade made for tile grout, then turn on the power and lightly apply it to the grout straight on.
The blade should remove the grout without a lot of pressure from you. After you’ve removed the visible grout, angle the blade slightly to reach the grout hidden just behind the tile—but work slowly and carefully to avoid damaging the tile.
After you’ve removed as much grout as possible with the power tool, use a flathead screwdriver to knock out any loose pieces that are still hanging on. Then remove any leftover grout using the manual methods described above.