Things You'll Need
Foam backer rod
Rag or sponge
In the process of updating and maintaining a home, you'll find yourself caulking and recaulking many times. Sound caulk joints in a bathroom or kitchen are a huge part of making sure that your home isn't damaged by moisture. Caulking is relatively easy to do, and most home owners get pretty good at it during their first caulking project. Sometimes, however, you have to caulk a gap larger than a single bead can properly fill. To make sure these gaps are as well sealed as your others, follow these easy instructions.
Remove all old caulk from the joint to be filled. Most caulk can be scraped away with a putty knife and sharp single-edge razor blade.
Measure the size of the gap that needs to be filled. A single bead of caulk can fill gaps up to 1/4 inch. If the gap is slightly larger than this, fill it with a bead of caulk deeper into the gap, but not flush with the surface. Wait until the caulk is completely cured before coming back to put a surface bead on. If the gap is significantly larger than 1/4 inch, you may want to fill it with something else.
Fill larger gaps with foam backer rod, sometimes called spline. This can be found at well-stocked hardware stores, but not always at large home improvement centers. Also, check concrete supply centers, as backer rod is used to fill gaps in poured concrete walls. Push the appropriate size backer rod into the gap, below flush with the surface.
Put a surface bead of caulk over the filled gap. Use only as much caulk as you need.
Smooth the caulk as you go. If using a water-based caulk, smooth it with a damp sponge or rag. If using a silicone caulk, smooth it with a damp finger. Wipe your finger frequently on paper towels, as silicone caulk is not water washable.