That classic old tile on your bathroom floor may be in great shape, but if the grout between the tiles is damaged, crumbling or deeply stained, the whole floor looks bad. Consider regrouting, which will make the whole floor look like new. The most difficult part of regrouting is removing the existing grout. You can scrape it out manually with a straight blade, called a tile saw, but for an entire floor, you should use a grout-extraction disk that attaches to your drill.
Set up your power drill with its grout-extraction disk.
Position the disk vertically over the start of the first grout line (so the drill itself is held sideways over the surface of the floor) and start the drill. Slowly lower the disk into the grout. Stop when you feel resistance, which will indicate you're at the bottom of the grout line, generally ¼ inch down.
Move the bit along the length of the line slowly, letting it pulverise the grout. Use caution not to scratch the tile itself. Break up the whole line of grout. Repeat for each line.
Go over each line with a hand-held vacuum, pulling out the pulverised grout.
Pour roughly equal amounts of water and grout powder into a bucket (approximately 1 inch each to start with) and mix well with a wooden spoon. Add more water and powder, making the grout about the consistency of cake frosting, and making enough to regrout all the lines.
Let the mixed grout sit in its bucket for about 10 minutes so the elements can meld. Stir it again.
Use a rubber grout float to spread the mixed grout over the surface of the tile, scraping it over the tile face with the long edge of the float. Allow the grout to stand in the lines for approximately 10 minutes. Use a damp sponge to wipe off the excess grout. Let it set for 48 hours before using the floor.