Caulk needs to be reapplied regularly, depending on how often you bathe or shower and how much of a mess you make each time. Overzealous housekeeping can also speed the deterioration of caulk Wet-mopping the bathroom floor and squeegeeing shower doors and walls pushes excess water up against the caulk line.
If you shower daily, you might need to recaulk every 18 months or so. But you can do several things to make your caulk last longer: When you shower, close the door or curtain completely, so no water runs down the outside of the tub.
Telltale signs your caulk needs replacing cracks, peeling and discoloration (usually orange or black). Applying caulk is a cinch. All the elbow grease and aggravation comes in digging out the old caulk. Count on two hours for a tub.
First remove the old caulk using a disposable utility knife. Be carefull not to scatch the tub surface. Just scape along the grout line. Be sure to get all the grout off and clean the surface before reapplying the new grout. You should use a product called Tilex to remove any resadue from the area. You can also use a home solution of 1/4 cup of bleach mixed in one quart of water.
DAP seams to make the best caulking products around. A tube of DAP Kwik Seal
Plus Kitchen and Bath Adhesive Caulk with Microban, an anti-microbial agent
that retards mold growth costs about $3.50. One 5.5 ounce tube should do two tubs.
Apply the new caulk by squeezing a "bead" as thick as a line of toothpaste; smooth it with your forefinger. Keep a small pail of water and a rag nearby for cleaning excess caulk off your finger and the tub. Let the caulk dry for 24 hours and you're done.