Ceramic tile is a standard for kitchen counters because it's nearly indestructible, resisting burns, stains, scratches and dents. But there are some weak links: grout for one, and too often counters that aren't built solidly enough to keep a tile job from cracking. And then there's the maintenance.
Clean moldy and stained grout. Use a proprietary cleaner, or for stubborn deposits a paste of household bleach and a scouring powder that does not contain ammonia. (Never combine ammonia and bleach.) Scrub it on with a brush and rinse. If discoloration remains, apply more paste and cover with plastic to keep in moisture, even overnight, before rinsing again.
Clean soap residue on grout. Soak deposits with an all-purpose cleaner, then scrub and rinse. On stubborn deposits, try a specialized product such as Tilex Soap Scum Remover, or a poultice of baking soda and liquid detergent left on the spot for several hours.
Replace loose grout. Even small cracks can let in water that eventually breaks the adhesive bond under tiles, and problems accelerate if the grout is loose or spongy. Those seams have to be cleaned out and regrouted. If nearby tiles are secure, clear away damaged material using a hand grout saw or a power saw (like a tiny router). It's faster but more difficult to control. Then mix new grout, test for a good color match, force the mix into the seams with a squeegee and finish with repeated damp sponging to remove the grout haze on adjacent tiles.
Seal grout. Over a clean, dry countertop, reduce maintenance and repairs by coating sound grout with a silicone sealer.
Use an artist's brush (it's painstaking work) or a special roll-on applicator made for the job.
Remove a damaged tile. Typically, you need to drill a line of holes (along the crack if there is one) to pop out a damaged tile in two pieces. If the bad tile is locked in grout, also drill the seams to gain leverage along an edge. If the damaged tile is surrounded by loose grout, scoring the tile edges with a utility knife or grout saw should free it.
Set replacement tile. Use a sharp chisel or utility knife to cut away the raised ribs of old adhesive. If you skip this step the replacement tile will ride too high. Then spread fresh adhesive with a notched trowel. If you're replacing only one or two small tiles and a notched trowel won't fit, load in adhesive and nestle the new tile in place so it's level with the counter. Work the new tile side to side to get full contact with the adhesive, and be sure to leave it centered in the space with even grout seams at the edges. It may be helpful to use a few strips of masking or painter's tape over several adjacent tiles to keep the replacement in position. When the adhesive sets (typically overnight), you can add grout to finish the repair.
Repair isolated water damage. If repair excavation reveals dark, damp, soft wood under the tile, keep digging to reach solid material. Scrape out the water damage, then bleach, and let the area dry. On deep damage, build up the depression with epoxy filler. When it cures you can set a replacement tile and complete the repair.
Fix leaks around sinks. To prevent leaks, sink edges should be set in a bed of putty, or better yet, silicone caulk. But that crucial seal may be incomplete, or wear away. You could reseal around the sink with a thin bead of silicone—like caulking around a tub. But particularly on self-rimming sinks (their edges overlap the countertop), it's better to release the counter clamps, raise the sink temporarily, and install a new bed of caulk. Let the silicone ooze out around the edges. When it cures you can peel away the excess.
Build rigid counters. To resist cracking, tile needs a completely rigid platform. The best bet is 3/4-inch-thick plywood, reinforced with additional strips of plywood for bracing, that is glued and screwed in place. For more stability and leak protection, cover the plywood with a layer of cement backerboard set with adhesive and screws.
Build the counter with the backsplash. Make the backsplash part of the assembly by gluing and screwing the plywood backer to the counter prior to the installation. This prevents separation and cracking at the longest seam along the top of the counter.