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How to recaulk a bathtub
Caulk fails in a predictable way: it shrinks, cracks, and grows mold from behind, and water starts slipping into the wall at every shower. The repair is simple and the rule is absolute: new caulk does not bond to old caulk. Every scrap of the old bead comes out, or the new one fails within the year.
Budget the time honestly. Removal and prep take most of the job. Laying the new bead takes fifteen careful minutes, and then the tub sits unused while it cures.
Tools required
- Utility knife and a caulk removal tool or single-edge razor scraper
- Painter tape
- Caulk gun
- Spray bottle with water and a drop of dish soap
- Paper towels and a trash bag at hand
Materials required
- 100 percent silicone caulk for kitchen and bath, mold-resistant, 1 tube
- Rubbing alcohol or denatured alcohol for final cleaning
- Painter tape as above
- Optional backer rod for gaps wider than about 1/4 inch
Step by step
Remove every bit of old caulk
Slice along both edges of the bead with the knife, then scrape the surfaces clean with the removal tool. Dig out soft or moldy material from the joint itself. If silicone residue remains as a shiny film, keep scraping: that film is exactly what new caulk will not stick to.
Clean and dry the joint
Vacuum or wipe out debris, then wipe both surfaces with rubbing alcohol to remove soap film and oils. Let the joint dry completely. Trapped moisture behind new caulk is the main cause of early mold.
Fill the tub with water
Before you caulk, fill the tub most of the way. A full tub sits lower on its supports, opening the joint to its working width. Caulk applied to an empty tub gets stretched and split the first time someone takes a bath.
Tape both sides of the joint
Run painter tape along the tub and the wall, leaving a gap slightly wider than the old bead. Tape is the beginner's best friend here: it guarantees straight edges and lets you tool the bead generously without smearing the surfaces.
Lay and tool the bead
Cut the tip at 45 degrees, smaller than you think, and apply a steady bead in one continuous pass per wall. Immediately spray lightly with the soapy water, then run one smooth finger stroke along the bead to press it in and shape it. Wipe excess on a paper towel, not back into the joint.
Pull tape and let it cure
Remove the tape right away, pulling it away from the fresh bead at an angle, and smooth any lifted edge with a wet finger. Leave the water in the tub and keep the shower dry for the full cure time on the tube, usually 24 hours.
Finishing and upkeep
Ventilate the bathroom during and after showers to keep the new bead dry in daily use. Mold starts on soap film, not on the caulk itself, so a quick rinse of the joint after showers extends its life by years.
When to call a pro instead
Call a pro if the wall around the tub feels soft, tiles move when pressed, or the subfloor near the tub is spongy. Those mean water has been behind the finish for a long time, and caulk is no longer the repair, it is the last step of one.
Questions homeowners ask
Silicone or latex caulk for a tub?
100 percent silicone, labeled for kitchen and bath. It stays flexible and waterproof far longer around a tub. Latex is easier to clean up and wrong for this joint.
Can I caulk over just the moldy section?
You can, and it will peel. Mold grows from behind failed caulk, so a partial patch traps the problem. Full removal of the run is the fix that lasts.
Why did my new caulk crack in a month?
Usually one of three causes: old residue left in the joint, the tub was empty during application, or the shower was used before the cure finished.