Regrouting tile restores its structural integrity and removes mold and mildew from the grout lines. Removal of the grout takes several hours, but an attachment for your hand rotary tool speeds the process. Other tools include a sponge, shop vacuum, grout float, flat head screw driver and rubber gloves. Purchase grout appropriate for the size of the joints between the tiles.
Remove the grout
Use the grout tool to cut away the old grout. The screwdriver helps to remove any stubborn grout. Use the shop vacuum to clean up the area and keep dust under control.
Apply the new grout
If working in a bathroom or other area where the surface is often wet, consider using a polymer grout with a mold inhibitor. Mix the grout according to the manufacturer's directions. Use the float to apply the material, taking care to work it into all the cracks. Work the grout in a diagonal direction to the grout lines.
Sponge the surface
After about 20 minutes, depending on the humidity in the area, the grout forms a white glaze over the tiles. Use a damp sponge to wipe away the film, being careful that you don't remove the grout from the lines. Allow it to dry for a week before applying a grout sealer.