How to Recaulk a Bathtub or Shower So It Stays Sealed

The caulk line where a tub or shower pan meets the wall is a waterproof seal. When it cracks, pulls away or turns black, water can get into the wall cavity behind the tile or surround, where it rots framing and grows mold out of sight. Recaulking is inexpensive and takes an afternoon, but caulk applied over old caulk or a damp joint fails within weeks. Preparation is the whole job.

Signs it is time

What you see	What it means
Black or dark spots in the caulk	Mold growing on or under the caulk
Gaps or the bead pulling away from tile or tub	Bond failure; water can get behind
Cracks in the caulk	Movement or old, hardened caulk
Soft or loose tile near the tub	Water already behind the wall: inspect
Water stain on the ceiling below	Possible leak through the joint or drain

Step 1: Remove all the old caulk

Cut along both edges of the old bead with a utility knife held at a low angle, then pull it out with a plastic removal tool. Work carefully on acrylic and fiberglass tubs, which scratch easily. Silicone leaves a film; scrape it off, then wipe the joint with rubbing alcohol to remove residue. New silicone does not bond to old silicone.

Step 2: Clean off mold

If the joint is moldy, clean it before sealing. The EPA recommends scrubbing mold off hard surfaces with detergent and water and drying completely, and wearing gloves, goggles and an N-95 respirator to avoid breathing spores. The EPA also warns not to paint or caulk moldy surfaces. If mold covers a large area, the EPA suggests professional help for growth over about 10 square feet.

Step 3: Let it dry completely

Caulk will not bond to a damp joint. Leave the area unused for at least several hours, ideally overnight, with the exhaust fan running and the shower door or curtain open. The EPA’s moisture guidance emphasizes that drying wet areas quickly is what prevents mold from returning.

Step 4: Fill the tub

For a tub, fill it with water before caulking. The weight lowers the tub slightly, opening the joint to its widest. Caulk applied this way is less likely to crack the first time someone sits in the bath. Leave the water in until the caulk has set.

Step 5: Tape and caulk

1. Apply painter’s tape on the tile or wall and on the tub, leaving a gap the width of the bead you want.
2. Cut the caulk nozzle at a slight angle to make a small opening; you can enlarge it later.
3. Run one continuous bead along the joint, moving steadily and keeping even pressure.
4. Smooth the bead with a wet fingertip or a caulk smoothing tool in one pass.
5. Pull the tape immediately, at an angle away from the bead.
6. Let the caulk cure for the time on the label, often 24 hours, before showering.

For gaps wider than about a quarter inch, press foam backer rod into the joint first so the caulk forms a proper seal rather than a thick plug.

Choose the right product

Use a 100 percent silicone or a product labeled for kitchen and bath use, with mildew resistance. Silicone is very flexible and long-lasting but cannot be painted. Acrylic latex caulks are easier to smooth and paint but are less durable in constant wet conditions.

Prevent mold from returning

• Run the bathroom exhaust fan during and after showers.
• Squeegee or wipe the tub joint after use.
• Keep the shower curtain or door open after showering so the area dries.

Common mistakes

• Caulking over old caulk.
• Caulking a wet or moldy joint.
• Using too much caulk and smearing it with repeated passes.
• Showering before the caulk cures.

When to call a pro

Call a contractor if tiles are loose or the wall behind the tub feels soft, if there is a water stain on the ceiling below that continues after recaulking, or if mold covers a large area or keeps returning quickly. Those are signs that water has reached the wall structure and that the substrate behind the tile may need repair.