This is something I get asked about in store quite often .. how to get clean tile grout, particularly shower tile grout, naturally without harsh chemicals.
We have two products that work wonders on tile grout, Green Goddess Premium Double Strength White Vinegar combined with either our Green Goddess Peppermint Cleaning Paste or Rose Cleaning Paste.
Put a good dollop of paste onto an old toothbrush, spray the grout and the brush with neat double strength white vinegar (regular white vinegar is not strong enough for tough cleaning jobs).
A chemical reaction will be created that’ll help to lift soap scum and clean the grout as you scrub. Add more vinegar if needed.
If cleaning a shower or sink wipe over the rest of the area with paste and vinegar on a cloth. Clean everything down with warm water and leave to dry.
To clean shower glass use the paste and vinegar mix on a cloth, wipe over the area very well, clean off. Then make a solution of 50/50 white vinegar and water, spray onto the glass and squeegee off for a streak-free finish.
If you have silicon grout that has gone black this method will clean the surface but won’t remove mould that has permeated the silicon, you’ll need to redo it if this has happened.