Caulking (glass silicone/window silicone sealant/glass sealant/construction sealant) is the preferred method of filling cracks between two adjoining materials or planes, such as where two wall materials meet in a corner, where a backsplash meets a countertop or a bathtub meets the bathroom floor. Not all corners need to be caulked, but there are a few areas within kitchens and bathrooms that benefit from the water and movement protection that caulking affords.
Any wet area in a kitchen or bathroom needs to be caulked to prevent water from soaking through and damaging the foundation materials beneath or behind, such as plywood and the wood framing for the home. This includes all interior joints within a shower, where the tub meets the floor and where the wall meets the tub, as well as around sinks, the backsplash-to-countertop joint in kitchens and the base of a toilet. The basic rule of thumb is that any joint that has the potential to regularly encounter water should be caulked as opposed to left open or grouted.
If there aren’t any water issues to be concerned with, consider whether or not the joint is visible or hidden. Not all hidden joints need to be caulked. Space is always left at terminate points to allow for natural expansion and contraction of the home due to weather, such as where the floor material meets the wall in a bathroom or where the backsplash material butts up against the bottom of the upper cabinets. But if these areas are hidden by baseboard or other items (such as underhanging lights on a cabinet set), you don’t need to caulk them because other materials keep the joints from view. If you desire, caulk the joints for added protection from dust and debris buildup over the years.
There are finish caulks and rough-in caulks, and both have their own uses. In visible areas, always choose some type of matching colored caulk (glass silicone/window silicone sealant/glass sealant/construction sealant/metal silicone). For tile installations, this is usually an acrylic or latex-based caulking that is sold by the same manufacturer as the grout in a matching color. Wood and other materials benefit from polyurethane caulking. All of these clean up with simple water and a sponge. Silicone caulking is best used in installation settings where it isn’t visible afterward because it is difficult to work with and can be cleaned up only with mineral spirits and vigorous scrubbing. You can use the clear type to caulk areas such as around toilets, bathtubs and sinks as long as you are careful with application and cleanup.
Any area where two hard materials meet up should be caulked. For example, you would caulk where the countertop meets the backsplash, where a tile floor meets a hardwood floor, along a threshold in a doorway, or where the tile or wood floor butts up against the bottom edge of a base cabinet. This is regardless of the presence of moisture. Because the two different materials are always expanding or contracting in separate manners, there needs to be a buffer between them to allow for this movement without allowing the gap to simply remain open to collect dirt and grime. This is also true of same-material butt joints, such as tile-to-tile.
For most jobs, caulking is applied with a caulking gun and a tube of caulk. Insert the tube into the caulking gun, then cut the tip off with a utility knife. Marks on the tips of caulking tubes show you how wide the opening will be depending on where you cut it. For best results, cut the tip off slightly smaller than the cracks you are filling. Insert the tip into the crack, squeeze the gun handle and fill the crack until it is full with caulking while moving the gun slowly along the void. Your finger can serve as the smoothing element, or you can use a putty knife to smooth the caulk across the surface of the joint; a damp sponge cleans up any excess. For silicone caulking, mineral spirits will clean up excess. Caulking is also available in squeezable tubes for smaller applications.