Changing the colour of your tile grout not only spruces up the room's appearance--it also protects the grout. Grout colourants are a water-based acrylic coating that help seal the grout joints as they dye the surface. Your tile grout will be more resistant to dirt, grease, and oil. Choose a grout colour that is at least one shade darker than the current shade if you want to avoid multiple coats.
Clean the grout thoroughly using a tile and grout cleaner designed to remove mildew, oils and soap scum. Scrub the grout with a sponge and then rinse the surface to get rid of the soap residue.
Allow the tile grout to dry for at least four hours. Place a fan in the direction of the grout if you want to expedite the drying time.
Apply the grout colourant with a small paint brush or paint sponge. Work in areas of no more than 10 square feet at one time. Use a thin coat of colourant, and rub the brush or sponge back and forth over the grout.
Allow the grout colourant to dry for at least 30 minutes. If the colour is not dark enough, apply another thin coat and allow it to dry.
Use a damp nylon scrubbing pad to to clean the tile--avoid scrubbing the grout. A damp paper towel will allow you to work along the very edges of the tile. Allow the grout to to dry for at least 24 hours before you return the surface to normal use.
Do not use grout colourant on porous stones or tiles, such as marble.