Oscar the Grout

An ounce of prevention...

Grout is the perfect example of this principle. Make sure it never gets the opportunity to mold, because once you've got mold, it will keep coming back. (Yes... the black stuff is household mold and it will create spores you breathe.) What would take you seconds in prevention will make you frustrated and take hours to clean.  Grout is a porous substance to hold the tiles in place, but it actually doesn't do well when it remains wet or damp because the water actually seeps into it. It's a great medium to grow mold. Once it begins getting mold, it gets harder and harder to get rid of as it grows and deepens.

• Keep good ventilation of grouted spaces and let it dry as completely as possible
• Clean it regularly - take the Lazy route and put undiluted white vinegar in a spray bottle and spray the whole thing weekly for a heavily used bathroom or monthly for a lightly used, well ventilated one. Let it sit for about 15-20 minutes and then rinse with water. I'd suggest doing this with open windows - it doesn't smell like roses but there are no harsh chemicals. This works because vinegar is acidic and 80% of mould cannot survive in that environment.
• Keep your grout maintained so it never molds and you will save hours and hours of cleaning time and grief

If you do see a spot of mold, use the toothbrush and vinegar. Don't even rinse after... because if a little of the vinegar seeps deep into the grout, it can kill the spores living there.Vinegar can work with most household molds and is mild.

If you get some mold and want to use a harsher chemical, fill a clean spray bottle with 50/50 bleach and water and spray the whole surface. Scrub the mold spots with bleach and the toothbrush. Rinse after 10 minutes.

Important - This solution is for tiles. If you have a porous stone (marble etc), acids such as vinegar will etch your surface. This tip will not work for you.