Old white grout is prone to staining and discoloration over time. Use oxygen bleach to clean your grout with strong fumes. Oxygen bleach kills mold and mildew, as well as whitening and shining your grout.
Instructions
1 mix water and oxygen bleach into a spray bottle. Add one tablespoon of oxygen bleach to each cup of water. Shake well until dust completely dissolves.
2 Spray the grout thoroughly with the mixture. Leave to act for 30 minutes at one hour. Spray grout again as needed, making sure it stays saturated all the time.
3 Rub the grout with a brush to loosen and remove any debris. Rinse thoroughly with a bucket of clean water.
4 Dry the grout with a towel. It looks darker than normal until the inside is completely dry.