Can you explain what I need to do to clean and restore or replace the grout in my tiled shower? The tile is 4″ x 4″ with white grout, and mildews black weekly.
Cleaning grout begins with eliminating the source of the mildew problem. The place to start in this case is to reduce moisture in your bathroom. If the space were properly ventilated, that mildew wouldn't be making a weekly appearance.
One way to stop the show and related health threats is to install a heater/han/light. A combination unit provides powerful ventilation, heating and lighting at the touch of a switch, and has a quiet fan and directionally adjustable heating vent. For best results, vent this unit to the outside of your home, and make sure all family members run the fan while showering.
After your bathroom's ventilation problem is solved, restore badly deteriorated grout surfaces by using a grout saw to scrape out the existing grout material, and replace it with an antimicrobial product that'll resist future settlements of stain-causing mildew and mold.
Laticrete offers a great solution for this step with its antimicrobial 1500 Sanded Grout and 1776 Grout Admix, both of which contain the mold-and-mildew-inhibiting protection of Microban, and also eliminate the shading and blotching caused by minerals and organic particles commonly found in domestic water. With a the addition of an anti-microbial grout, cleaning grout in the shower will become a thing of the past.