One of the best ways to help prevent mold and mildew is by learning how to seal grout. Once you learn how to seal grout, you will be much more effective at keeping moisture, and dirt out of your grout lines. If you apply two or three coats of a grout sealant, it becomes waterproof. Ordinarily, grout is very porous and will absorb anything that comes into contact with it, but once you apply a grout sealer it creates an impenetrable, waterproof barrier between your grout lines and whatever else happens to fall on the floor.
The first thing that you can do to create a formidable line of defense is to apply a good quality grout sealer. In order to do this, you typically use a paint brush, or a roller brush and you make sure to apply the sealer to all of the grout lines. For best results, you want to make sure that you apply the grout sealer at least once every 6 to 12 months. In addition, if your grout starts to get dirty at a rate that is faster than normal, it may also be a good time to clean it and to reapply a grout sealer to it.