Old, cracked or moldy caulk around a bathtub is more than an eyesore. That bead is what keeps water from seeping behind the tub and into the wall or subfloor. When it fails, you can end up with hidden rot, loose tiles and mold you can’t scrub away.
Re-caulking is inexpensive and doesn’t need special skills, but it does reward careful prep. The difference between a messy, short-lived job and a crisp bead that lasts for years is almost entirely in how well you remove the old caulk and clean the joint.
When to Re-Caulk
Replace the caulk if you see any of these:
- Black or pink spots that don’t come off with cleaning (mildew growing into the caulk)
- Cracks, gaps or sections pulling away from the tub or tile
- Caulk that feels soft, gummy or crumbly
- Water appearing on the floor or ceiling below after showers
It’s also smart to re-caulk after any tub or tile repair, or when you move into a home and don’t know the caulk’s age.
Choosing the Right Caulk
Not all caulk belongs in a bathroom.
- 100% silicone sealant: The usual choice for tub-to-tile joints. It stays flexible, sheds water and resists mildew well when labeled for kitchens and baths. The downsides: it’s harder to tool neatly, and paint won’t stick to it.
- Siliconized acrylic (latex) caulk: Easier to apply and clean up with water, and paintable, but generally less durable in constantly wet areas. Better for trim and dry joints.
- Hybrid polymer sealants: Some newer products combine easier tooling with silicone-like flexibility. Read the label for “tub and tile” or “kitchen and bath” ratings.
Look for a product labeled mold- or mildew-resistant, and pick a color that matches the grout or tub (white, almond, clear, or a grout-matched color). Well-known options include GE Advanced Silicone and DAP Kwik Seal or DAP Silicone Plus, among others.
Tools and Materials
- Caulk in a standard cartridge, plus a caulk gun with a smooth trigger (or a squeeze tube for small jobs)
- Plastic razor scraper and a utility knife or single-edge razor
- Caulk remover tool (a hooked plastic tool helps get old caulk out of the joint)
- Silicone caulk remover gel, if the old caulk is silicone
- Isopropyl (rubbing) alcohol and clean rags
- Mildew cleaner or a diluted bleach solution (never mix bleach with ammonia or acidic cleaners)
- Painter’s tape (optional but helpful)
- Paper towels, gloves and a small trash bag
Step 1: Remove All the Old Caulk
New caulk doesn’t bond well to old caulk, especially silicone. Get it all out.
- Slice along both edges of the old bead with a utility knife or razor, held at a shallow angle so you don’t scratch the tub.
- Pull the bead out with your fingers or a caulk remover tool.
- Scrape remaining film with a plastic razor. For stubborn silicone residue, apply a caulk remover gel, wait as directed, then scrape again.
- Vacuum or wipe out debris from the joint.
Take your time. Leftover silicone is the most common reason new caulk peels.
Step 2: Kill Mildew and Clean
Spray the joint with a mildew cleaner and let it sit according to the label, then rinse thoroughly. Mold that has grown deep into the gap needs to be killed before you seal over it.
Once rinsed, wipe the joint with isopropyl alcohol to remove soap scum and oils. Alcohol also helps it dry faster.
Step 3: Let It Dry Completely
This is the step people skip. Caulk applied over a damp joint can fail early and trap moisture. Let the joint dry for several hours or overnight. Run a fan or open a window. Don’t shower in the meantime.
Step 4: Fill the Tub With Water (Optional but Smart)
A tub flexes slightly when full of water and a person. If you caulk an empty tub, the bead can be stretched and crack the first time the tub is used. Many pros fill the tub with water before caulking and leave it full until the caulk cures. This applies especially to acrylic and fiberglass tubs.
Step 5: Tape the Lines (Optional)
For the cleanest result, run painter’s tape along the tub and along the tile, leaving a gap the width you want your bead (usually around 1/4 inch). The tape gives you perfectly straight edges. You’ll pull it right after tooling.
Step 6: Apply the Caulk
- Cut the cartridge nozzle at a 45-degree angle with a small opening. You can always cut more.
- Puncture the inner seal with the gun’s poker wire or a long nail.
- Start in a corner. Hold the gun at a 45-degree angle and push or pull it along the joint with steady trigger pressure, moving at a consistent speed.
- Work in sections of a few feet at a time so you can tool the caulk before it skins over (silicone skins quickly).
- Release trigger pressure at the end of each run; many guns have a release to stop the flow.
Step 7: Tool the Bead
Smooth the caulk right after applying it. Options:
- A caulk finishing tool with rounded profiles
- A gloved fingertip dipped in soapy water (for silicone) or plain water (for acrylic)
Use one smooth pass, pressing lightly to push caulk into the joint and create a slightly concave bead. Wipe excess off your tool frequently. If you taped, remove the tape immediately after tooling, pulling it away from the bead at an angle.
Step 8: Let It Cure
Check the label: many silicones are “shower ready” in a matter of hours but take longer to fully cure. Wait the full recommended time before showering. If you filled the tub, drain it only after the caulk has cured.
Tips for a Professional-Looking Finish
- Work in good light, and keep paper towels in your pocket.
- Don’t overfill. A thin, even bead looks better and cures properly.
- Gaps wider than about 1/4 inch may need foam backer rod pushed in first so the caulk isn’t too deep.
- Ventilate the bathroom well, especially with solvent-based products.
Keeping New Caulk Clean
- Run the exhaust fan during and after showers.
- Squeegee or wipe the tub edge after use.
- Clean regularly with a mild bathroom cleaner instead of letting mildew establish itself.
Frequently Asked Questions
Can I caulk over old caulk?
It’s not recommended. New caulk bonds poorly to old caulk, and you’d be sealing in any mildew underneath. Remove the old bead completely.
How often should a tub be re-caulked?
There’s no fixed schedule; it depends on product quality, ventilation and cleaning habits. Inspect it a couple of times a year and replace it when it cracks, separates or stains permanently.
Why did my new caulk turn black quickly?
Usually because mold wasn’t fully killed before caulking, the joint wasn’t dry, or the bathroom stays humid. Improve ventilation and redo the job with thorough cleaning.
Silicone or acrylic for a bathtub?
For the tub-to-wall joint that gets constantly wet, 100% silicone or a sealant specifically rated for tub and tile is the common choice. Acrylic is easier to use and paintable, but better suited to drier areas.
What if water is already getting behind the tub?
If you see soft drywall, loose tiles, or stains below the bathroom, caulk alone may not solve it. Investigate the source, and consider a professional inspection for hidden water damage.
The Bottom Line
A good re-caulk job is about 80% prep: remove every trace of old caulk, kill the mildew, and let the joint dry. Then lay a steady bead, tool it once, and let it cure fully. It’s an afternoon project that protects your bathroom for years.
Editorial note: Fix It Folio is independent and reader-supported. This guide is based on research into manufacturer documentation, published specifications and widely accepted best practices; we have not been paid to mention any product. If we add affiliate links in the future, they will be clearly disclosed per our Affiliate Disclosure.