Old tile grout may become dirty and stained over time. Cleaning grout and applying a sealer will make future cleaning much easier. It is important to properly clean old grout so that the grout sealer will adhere correctly.
Cleaning Old Grout
Sweep the tiled floor and grout lines thoroughly. Use a broom or soft-brush vacuum cleaner attachment to remove loose dirt, dust and debris from the floor.
Mix up a homemade grout cleaner in a bucket. Mix 1/3 cup household ammonia, 1/4 cup white vinegar, 7 cups water and 1/2 cup baking soda. Stir the ingredients with a long-handled spoon to thoroughly combine.
Apply the mixture to the old grout using a sponge. Make sure to thoroughly saturate the grout. Work in sections of about 2 square feet so that the cleaning solution does not dry on the surface. Allow the mixture to sit on the grout for a few minutes.
Scrub the grout with a damp rag. For tough stains, use an old toothbrush to scrub the grout.
Wipe down the grout with a dry rag to remove any moisture. Allow the grout to air dry the rest of the way.
Use tea tree oil to clean mold and mildew from old grout. Combine 2 cups water with 2 tbsp. tea tree oil in a clean, empty spray bottle.
Spray the solution onto the moldy areas of the grout. Allow the solution to dry on the grout without rinsing. The mold and mildew will be gone once the solution evaporates.
Sealing Old Grout
Choose the appropriate sealer. A variety of grout sealers are available. A water-based sealer will work best for sealing old grout. Choose a sealer that comes in a bottle with a flip-top applicator.
Let the grout dry completely from cleaning.
Shake the bottle of grout sealer. Place small drops of sealer 1/2 inch apart along the grout lines. Work in sections of about 1 square foot so that the sealer does not dry before you have a chance to spread it.
Use an old toothbrush to evenly spread out the grout sealer. Use a scrubbing motion when spreading the sealer to ensure that it penetrates the grout.
Wipe off any excess grout sealer from the surrounding tiles with a damp rag. Use caution not to wipe the grout joints.
Allow the grout sealer to set for 30 to 60 minutes, or the time recommended by the grout sealer manufacturer. Clean the grout with a damp rag once the sealer has set. Go over the grout lines with a dry rag to remove any haze.
Apply a second light coat of the sealer if recommended by the manufacturer. It is best to apply two light coats rather than one thick coat. Clean the grout lines a second time with a damp rag, followed by a dry rag, if you applied a second coat of sealer.