Tile – Suggestions on tile edging

You likely need more coats of sealer. Depending on the porousness of the tile and the quality of the sealer you may just need more to get the job done.

When you do the shower walls, I would follow these steps:

1. Make sure your wall is waterproof - good suggestions from @Shimon Rura.
2. Install your tiles.
3. Apply two thin coats of penetrating sealer. Leave each coat on for at least 10 minutes before wiping off (or follow the instructions).
4. Grout the tiles, using sealer instead of water in the grout.
5. Clean the tiles very well, allow to dry. Apply two more thin coats of finishing sealer.

If you're using the glossy sealer this might be a bit much. I would use the clear penetrating kind for the pre-grout coats.

The pre-grout coats are not strictly necessary, but do serve two purposes. The first is that if you have porous tile it will give you the extra protection you need. The second is it makes cleaning up the grout easier if you're sloppy. Adding sealer to the grout is supposed to help with bonding it to the thinset - not sure if that's true, but if you have extra on hand it works fine.

If there is moisture still there, then mold and mildew will return. If the problem was not fixed, then it will return. Bathrooms are particularly bad in this respect, since moisture is a natural consequence of using water. I would expect to need to redo things like caulking every few years to fix this. It will not last forever.

1. Scrape/pull off the old silicon.

2. Apply a solution of bleach to kill the mold. Be careful when you apply it, as bleach can damage the clothes you are wearing. Keep the area ventilated well.

3. Let it dry. If you are in a hurry, a fan blowing on the area will help. A hair dryer can also speed that process considerably.

4. Apply new caulk in a smooth bead. I use my finger to spread it along the joint. Definitely use a high quality silicon caulk with a mold/mildew inhibitor. These are caulks that are designated for use in bathrooms.

5. Allow it to fully dry before you get it wet again. Give it a day or so. It will skin over in an hour or so, but make sure it has properly cured before use of the shower.

Expect to redo this process in some number of years. The exact time it will last depends on how well the area is ventilated.

Of course, there may be mold in the wall itself. This is difficult to deal with unless you tear the wall down to replace it completely, and even then water tends to attract the stuff. Mold spores are everywhere.