Grout the tile. Mix up a batch of grout and let it rest for 5 to 7 minutes. Lightly wet the area you’ll be grouting with a damp sponge and dump a bit of grout onto the area. Use a rubber float to smooth it into the joints, attacking each joint at a diagonal angle. After 30-40 minutes (check the directions on the bag of grout) you want to wipe the excess grout with a damp sponge and a circular motion.
Keep wiping with a clean sponge until the tile is clear. The tiles may look a bit hazy even after wiping, so you may have to buff them with a clean sponge to get rid of this haze. Let the grout cure for approximately 3 days before sealing. Then, seal the grout. Run a thin bead of liquid grout or aerosol grout sealer onto the grout line and wipe away.
Let dry and then test its water resistance by dropping water onto the sealed grout. Correctly sealed grout will cause the water to bead up on top of it. Caulk any needed areas. Make sure to use a grout caulk to match the colors. As you caulk, remember to pull the caulk gun relatively quickly across the joint.
Most amateurs caulk too slow and end up dropping too much caulk down on the joint. Other things to remember: Keep the tip angled as you run the bead along the joint. Match the speed with which you pull the caulk gun trigger with the rate at which you pull the gun along the joint. You don’t want to be pulling the gun fast but triggering slowly, or vice versa.
After applying the bead of caulk, “bed” it by running a damp finger across the bead with light pressure. Make sure that your grout chalk matches the grout. Let the caulk dry and redo it if you are not happy with the results. Let the tile set for 48 hours. This will make sure that the mortar has adhered properly to both the tile backing and the cement board backer.