We had our bathroom renovated this past summer. Our new shower stall has a plastic base and ceramic walls. The caulking at the bottom seems to dip. It forms a low point where water collects and gets mildewy quickly. Can I add a layer of caulk to this or must I remove the old caulk completely and start over? What kind of caulk should I use?
Remove the old caulk completely, with a razor blade or similar. The wrong type caulk was installed. Silicone caulk specifically made for bathrooms has a mildewcide in it which slows or stops mildew growth. That is what should be used.
There are a number of ways to smooth that caulk bead so there is no place for water to pool. I just use a finger, but some used a wetted finger, spoon, another type of curved tool, etc. Kepp a rag or paper towel to keep wiping the tool so the caulk does not pile up behind it. But don't put in too large a bead.