You will need
  • - small brush or sponge;
  • tool for cleaning;
  • - the steam cleaner;
  • pen with water-resistant dye;
  • - water-resistant water-based paint;
  • - fine sandpaper.
If the joints between the tiles become gray and dirty, apply a small brush (e.g. toothbrush) any kind of detergent (Silit, Cif or other). After 10 minutes, wash the tiles with water and wipe dry. If the contamination is left, then it's a fungus, and it is difficult to bring cleaning products.

For the removal of contaminants alternative to chemical compositions may be: baking soda, diluted lemon juice, vinegar, mustard, toothpaste, ammonia, or fine salt.
If the fungus appeared, the seams can be cleaned with chlorine-containing means (Domestos, White or other). They must apply using a small brush or sponge for five minutes, then rinse with water and wipe dry. The result destroys all germs, clean the mildew, the seams are clean.
If the fungus is covered with small areas of seams, they can be masked with a Sharpie with fotostock dye. This can be done pretty quickly, but the effect will be short-lived. Pens can be purchased in stores of construction materials.
If the fungus geodaetica to bring a cleaning or bleaching funds, and the area of contamination is large, do not rush to change the grout. Try to paint the tiles with any water-based waterproof paint. It is advisable to apply several layers.
A steam cleaner is another proven way to clean joints from dirt. Need to focus on seams the nozzle of the steam cleaner cleans with hot steam and then wash off the dirt with water and wipe dry.
Fungus and dirt can be cleaned from the tiles with fine emery paper. It will remove the top layer of grout, and at the same time, and pollution.