To prevent some cement-based grouts from drying prematurely, wash white-bodied and soft red-bodied tiles before grouting. These types of tiles tend to be a lot more porous and can draw liquid from the grout and make it weak.
For standard 4 1/8-inch tiles where the joints are very narrow, use non-sanded grout. For any other grout joints with other types of tiles, use a sanded grout, which holds up better when the grout lines are wider.
The easiest way to apply grout is with a rubber-faced float or a squeegee, although you can do it with your finger and a large sponge. An old toothbrush is handy too to help work the grout into the joints.
It is best to mix the tile with a 50/50 mixture of water and grout fortifier. It will make a more watertight seal.
The following are the steps in applying grout:
Apply grout to the surface of the tile, spreading it with the float or squeegee and forcing it into the joints. It is critical that the joints be completely filled so that there are no bubbles or gaps.
Scrape the excess grout off by wiping diagonally across the tiles with your float or squeegee.
With a cleaned out sponge washed out in clear water and wipe away any remaining grout. Wipe the grout away as you go. Grout an area, then wipe it down. Don't wait until you've grouted the entire area. Continue to rinse and wring out the sponge until the joints are smooth and level with the tiles.
Let the tiles dry out. After about 30 minutes a hazy grout film will appear. Wipe that away with a soft cloth. You can use the end of a toothbrush handle to tool the joints and clean the intersections.
Installing Soap Dish and Other Accessories:
After you have laid your field tiles and the adhesive has dried, you can go ahead and install the soap dish and the towel rack.
Often, on the backside of the ceramic soap dish and towel rod accessories, there are small holes. These holes should not be covered up in the course of buttering the adhesive on the back as condensation can build up inside of them and cause them to pop off the wall.
Run a bead of silicone caulk around the edge of the tub where the tile meets it along the top and the base at the floor level. Also, caulk around the plumbing pipes and behind the rims of the soap dish and any towel rods.
After the grout has completely dried and cured you'll want to seal the grout. For inside corners, use a silicone based caulking that will hold up well. You should wait between 3 days and 2 weeks before you apply the sealer so read the manufacturer's label on the grout and sealer to be sure of the correct dry time.