Dirt naturally accumulates in the grout joints, turning them black and unhygienic. To clean natural stone tile joints, we recommend using a non-aggressive alkaline product like PS87 PRO Heavy Duty Cleaner, diluted 1:5-1:10. Scrub vigorously with an abrasive pad and rinse thoroughly.
Once the surface is clean and dry, you can complete the stain protection treatment with the product most suited your type of natural stone.