Cracked, moldy caulk around a tub looks bad, but the real problem is hidden. Every shower sends water into that gap, and over time it can soak the subfloor or the wall behind the tile. The fix is cheap and quick. Learning how to caulk a bathtub takes one afternoon, and a good bead lasts for years.
Tools and Supplies for Caulking a Tub
You don’t need much. Pick up these before you start:
- 100% silicone caulk labeled for kitchen and bath (it stays flexible and resists mold)
- A caulk gun with a smooth trigger
- Plastic caulk removal tool or a utility knife
- Rubbing alcohol and clean rags
- Painter’s tape
- A small cup of soapy water
Skip acrylic “tub and tile” caulk for the joint where the tub meets the wall. The tub flexes a little when it fills with water, and silicone handles that movement much better.
How to Remove Old Bathtub Caulk
New caulk won’t stick to old caulk, so this step matters most. Slice along both edges of the old bead with the removal tool, then peel it out in strips. Stubborn bits come off with a plastic scraper. Avoid metal blades on acrylic or fiberglass tubs because they scratch easily.
Once the old bead is gone, scrub the joint with a mildew cleaner if you see black spots. Then wipe everything with rubbing alcohol to remove soap film. Let the joint dry completely. Overnight is best. Caulk applied to a damp gap will peel within weeks.
Fill the Tub Before You Caulk
Here’s a pro trick most people miss. Fill the bathtub with water before caulking. The weight pulls the tub down to its lowest position, so the gap is at its widest. When you drain it later, the caulk gets compressed instead of stretched, which means fewer cracks.
How to Apply a Smooth Caulk Bead
Run two strips of painter’s tape along the joint, one on the tub and one on the wall, leaving a gap about 1/4 inch wide. Cut the caulk tube tip at a 45-degree angle, just smaller than the gap.
Hold the gun at the same angle and push the bead ahead of the nozzle as you squeeze. Move at a steady pace and work one full side of the tub at a time. Try not to stop in the middle of a run, because restarts leave lumps.
Tooling the Caulk Line
Dip a fingertip in soapy water and drag it lightly along the bead. This presses the caulk into the joint and gives it a slightly curved shape. Wipe your finger often. Pull the tape right away while the caulk is still wet, lifting it away from the bead at a low angle.
Curing Time and Aftercare
Leave the water in the tub until the caulk has set, usually a few hours. Most silicone needs 24 hours before it’s ready for a shower, so check the label. After that, keep the joint dry after bathing with a quick wipe or a squeegee. Good airflow does more to prevent mold than any cleaner.
Common Caulking Mistakes to Avoid
- Caulking over old, dirty caulk
- Using too big a bead, which smears and looks messy
- Getting the joint wet before it cures
If the grout between your tiles is also cracked or stained, handle that first. Our guide on how to regrout bathroom tile walks through the process. Then caulk last so the whole bathroom is sealed.
Keep Your Bathroom in Shape
Caulking is one of those small jobs that protects the rest of the house. Add it to your yearly seasonal home maintenance checklist, and while you’re in the bathroom, try replacing your showerhead for better water pressure. If a slow drain is bugging you too, here’s how to unclog a drain without chemicals.
