Steven L.:
I own a small apartment block, and cleaning ceramic tile grout of mildew stains isn't that hard to do.
Basically, the trick is to apply bleach straight out of the jug with a tooth brush. Often, however, this doesn't seem to do anything at all, and the reason why is that the surface of the grout is clogged up with soap scum. So, the bleach you're applying isn't being wicked into the grout because the soap scum is clogging up the surface of the grout and preventing it from wicking in that bleach.
So, the procedure to follow is to first open up the porosity of the grout by dissolving the very surface layer of grout using phosphoric acid. Phosphoric acid is the most commonly used active ingredient in bathroom cleaners because it cuts through soap scum like a hot knife through butter, but won't attack chrome even at high concentrations. The most common place to find phosphoric acid is in toilet bowl cleaners which will typically be 15% to 20% phosphoric acid. So, the way to do this is to squirt some phosphoric acid based toilet bowl cleaner on your ceramic tiling, remove it to the grout lines using a rubber squeegee, and scrub with a tooth brush to dissolve the top thousandth of an inch of grout that's clogged with soap scum. Then rinse the acid off with clean water and allow the tiling to dry at least overnight and an extra day after that would be better.
Now, use a toothbrush to apply bleach to the dried grout. Here, patience is a virtue because it may take some time for the bleach to penetrate deep enough into the grout to kill the mildew and thereby remove the discolouration. A common mistake is to only apply the bleach once. It's best to apply it every few hours and the discolouration will start disappearing. As it disappears, you still apply the bleach, but you're applying it to less and less grout.
If the bleach just doesn't seem to be working on an area, then give that area another shot of phosphoric acid, allow to dry, and start applying bleach again.
By the time you've spent a few days doing this, you'll find your grout should be pretty white, and if there are any areas that are still discoloured, you can simply replace the grout in those areas. You should cut the grout out fairly deep before regrouting. And of course, it's always easier to wipe grout down to a uniform depth with a damp sponge if you start with the grout at a uniform depth, so scrape the new grout down with a popsicle stick before wiping it down with a damp sponge.
Once your grout is clean, you want to seal it. Throw away any grout sealer you find with the word "siloxane" in it's ingredients. "Anything siloxane" means a silicone plastic. The problem with silicone based plastics is that nothing sticks well to them, and that's as true for silicone based grout sealers as it is for silicone caulks. So if you apply a silicone based grout sealer it will stick well to the grout. The problem is that a few years down the road you can't apply more silicone grout sealer to restore the protection because the new grout sealer won't stick well to the old grout sealer.
If you can, find an acrylic based film forming grout sealer. I like a product made by Glaze 'N Seal of California called simply "Grout Sealer", but if you can't get that, then Google "DuPont Stone Tech" and you should get a DuPont web site or at least some places selling DuPont Stone Tech Professional grout and masonary sealers. Check with the DuPont 1-800 number to see if they have an ACRYLIC film forming sealer. If you don't get anywhere going that route, then buy Tile Lab's "Gloss" Sealer and Finish or Tile Lab's "Matte" Sealer and Finish, both of which are acrylic film forming sealers. Tile Lab is a division of Custom Building Products (the same people that make Wonderboard). I can't say that I'm a screaming fan of either Gloss or Matte, but one of the things I do like about using these products is that Tile Lab's "Heavy Duty Cleaner and Stripper" really makes easy work of removing the Gloss or Matte grout sealer if either ever gets stained and you want to replace the grout sealer. But, that shouldn't happen and with acrylic grout sealers like Gloss or Matte, you can just apply more grout sealer to add more protection.
Post again if you have any questions on how to clean the grout, how to grout or how to seal grout.
You can also clean mildew of of silicone caulk, but that's a different procedure.
Hope this helps.
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