One of the simplest ways to make your shower tile look like new again is to remove the old grout and grout again.
Tile rescue tasks are made much easier with an abrasive cleaner that restores the tile to a smooth, shiny and new looking surface. Be careful, however, if you choose to do a tile rescue diy project job. Make sure you wear goggles and a mask so no particles get into your eyes or mouth during the tile rescue.
After removing the grout, use a sealer for glossy tiles (usually a silicone product) and apply it to the shiny surface. You can either apply one coat, or several coats. Just follow the instructions on the can of sealer when doing regrouting job.
During the regrouting job at home, once the grout is removed, you will notice that there are many holes in your shower wall tiles where the grout used to be. The best way to fill these holes is with a special filler that is made for gaps between tiles called Polymer Modified Joint Compound (PMJC). This stuff works like magic and once it dries it becomes almost impossible to tell where there were any gaps in the shower grout to begin with.
Before using this compound during regrouting, sand around all edges of the tile on the walls with 120-grit sandpaper tool to remove any roughness or uneven grout surfaces since most likely you won't be able to fill the grout lines with compound without a smooth surface. Proper grout lines are important.
After the grout has been applied, take help of a straight edge tool to smooth the compound around the edges of your tiles for proper grout lines. The tiles are now ready for a waterproofing sealant (especially on the joints) to eliminate water penetration since water penetration will introduce mould build up in the area and a shower can use a lot of water. The most popular is a waterproof silicone sealant for home. Following the application, and once the grout dries, you should be ready to take showers without worry. Remove any grout haze on the wall surfaces and shower tiles. Avoid excess grout in any area.It really depends on the condition, how old the grout is behind the tile before applying new grout. If the grout is old and has begun to turn or has stains, you can likely try cleaning it by hands simply using a toothbrush or an abrasive tile cleaner or something like that for cleaning before applying new grout. You could also try scrubbing by hand with a wire brush or sponge (hard sponge) for consistency and spots removal but be careful not to scratch the surface of your tiles. A tile is vulnerable to damage. However, if the grout is only a few years old and still in good shape, you might want to consider repairs and leaving it in place and avoid new grout. The reason is that when you remove tile grout, it leaves very small holes and the space underneath grout joints and allow water to penetrate in the bathroom walls. A better idea might be to apply a grout sealing product.
It really depends on what kind of look you want to achieve. Polymer modified joint compound is a great product that fills in the tiny holes left by removing old grout. But then the question becomes whether you should use glossy or matte finish sealer. The top coat can be a bit tricky. You have to make sure the sealer you use is compatible with your original grout, or it could chip away when used. Not all tile sealers are suitable for bathroom tiles. Try a small section in an inconspicuous place to see if it works first. You may use a proper tool or multiple tools such as a utility knife, rubber float and grout float. Wear a dust mask in the work area.
There are many different types of grout powder, from basic to specialty. Basic grout is designed for use on floors, shower regrout and in high traffic areas. It's also very easy to work with because it doesn't shrink as it hardens. To keep your bathroom floor looking clean and fresh, you can use a simple grey epoxy plastisol or cement-based grout that comes in a bucket. For specialty tiles, you can consider using coloured grout to really enhance the look of your shower. You might choose a semigloss or glossy grout sealer for this purpose. If you have especially complex tile arrangements, you may want to ask your hardware store for advice first since different grouts work better in certain situations than others.