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How to clean black grout in shower?
Tell me if it is white grout, that has developed a black mold condition, or if it is the very unusual, black tinted grout.. If that is the case, it will be black all over. if its white grout with mold, it will just be black in certain areas, the ones that tend to stay wet the longest. We can go from there. For white grout and black mold, begin by removing the old soap film that the mold feeds on... Use a sponge or dish rag first, then a stiff nylon bristle pot scrubber and liquid dish washing soap to scrub the entire inside of the shower area to get rid of all of the soap film and mold. Rinse completely. Then spray chlorox bleach solution onto the entire shower area, and let set for an hour. One cup of bleach in a quart sprayer, then fill the rest with water. Rinse with water. Then go over the area again with a scotch bright pad. (do not use it on a plastic or soft surface tub, check for abrasion first). Then spray with chlorox bleach again, let sit for 10 minutes and repeat the spray. After half hour rinse thoroughly. Do not mix commercial cleaners with bleach the process. It can create dangerous gassing. Repeat on any area the develops black mold as soon as it develops, that can be done quickly and the larger problem held at bay so to speak. Black mold in some forms can cause severe illness or difficulty in breathing etc. Most in showers however is not as toxic, but a person needs to be alert to the potential. If you keep it clean for a month, it may take a lot longer for the mold to return.
As is the trend, I used black grout with dark tiles. Some areas I would say soap scum, other areas where the grout seldom gets wet, far end of shower up high is still more of a grey. The only areas that stayed really black were some of the black caulking.
Since you have black grout, the situation is that minerals in the water is turning the grout gray where its not wet long enough to grow mold. And near the bottom of the tiled area, where it is wet a greater percentage of the time, it is growing dark back mold. The larger hardware stores carry tile grout cleaner as well. You may want to consider that, but, do not mix it with a chlorox and water solution. That can create very poisonous fumes. Use CLR scale remover to get rid of the scale causing the tile and grout to turn gray near the top. If you had not used a grout sealer when you did the original job, you may want to consider it after you have cleaned the grout. And it has had a day or two to dry. I would repeat this cleaning job two or three times in the space of a month, then when its completely clean, apply a sealer.