How to Replace Peeling, Moldy Bathroom Caulk — and Get a Clean Line

Peeling, cracked, or black-spotted caulk around a tub or shower isn't just ugly — it's a gap where water gets behind tiles and into walls. The short answer: cut the old caulk out completely, clean and dry the joint thoroughly, then lay a new bead of silicone caulk in one smooth pass and tool it with a wet finger. The removal and prep take longer than the new bead, and they are the part that decides whether the new caulk lasts two years or six months.

Removing the old caulk

Don't caulk over old caulk. A new bead stuck to a failing old one peels off with it, and trapped moisture underneath keeps feeding mold. Removal is the unglamorous core of the job:

1. Soften it first. Spray the old caulk with a caulk remover gel or soak a rag in rubbing alcohol and lay it on the bead for 15 to 20 minutes. This won't dissolve the caulk, but it loosens the bond. 2. Cut along both edges. With a utility knife or a dedicated caulk removal tool, cut along the top edge where caulk meets tile and along the bottom edge where it meets the tub. Keep the blade flat and shallow — you are cutting caulk, not grout or the tub surface. 3. Peel it out in strips. Grab an end and pull steadily; well-cut caulk often comes out in satisfying long strips. For stubborn bits, use a plastic scraper or a flathead screwdriver wrapped in a cloth. 4. Clean the joint completely. Scrub the bare joint with a bathroom cleaner or a baking soda paste to remove mold and soap residue, then wipe with rubbing alcohol. Any old caulk, soap film, or mold left behind stops the new bead from bonding. 5. Let it dry fully. This is the step people skip and regret. The joint must be completely dry — ideally overnight, or at least several hours with the bathroom ventilated and the shower unused. Silicone will not bond to a damp surface.

Laying a bead that looks professional

With the joint clean and dry, the new bead itself is quick:

• Use 100% silicone caulk for tubs and showers. Silicone stays flexible, resists mold better than latex, and handles the constant wet-dry cycle. Latex caulk is easier to paint over but breaks down faster in a shower. Pick a color that matches the grout or tile — white and clear cover most bathrooms.
• Cut the tip small. Cut the nozzle at a 45-degree angle with an opening about the width of the joint — a bead slightly narrower than the joint is easier to tool than one that overflows everywhere.
• Apply in one steady pass. Hold the gun at a consistent angle and squeeze with steady pressure, moving at an even speed. Stopping and starting creates lumps. If you do mess up a section, it's easier to wipe it out and redo that section than to patch over it.
• Tool it immediately. Wet your finger (or a caulk-smoothing tool) with water or a little dish soap solution and run it along the bead in one smooth motion. This presses the caulk into the joint and gives it the clean concave profile that sheds water. Wipe excess off your finger as you go.
• Peel painter's tape if you used it. Tape along both edges of the joint before caulking gives a crisp line, but peel it off while the caulk is still wet — waiting until it cures tears the edge.
• Don't use the shower for 24 hours. Silicone needs a full day to cure. A shower taken too soon washes uncured caulk out of the joint and you are back to square one.

Making the new caulk last

Good caulk in a bathroom lasts several years; bad conditions kill it in months. The main enemies are standing water and mold:

• Ventilate after every shower. Run the exhaust fan during and for 20 to 30 minutes after showering, or crack a window. A joint that dries between showers lasts far longer than one that stays damp.
• Wipe the bead dry occasionally. A quick towel pass over the tub edge after showering removes the standing water that feeds mold.
• Clean with non-abrasive products. Abrasive scrubbers rough up silicone and give mold more surface to grip. Mild cleaners and a soft cloth are enough.
• Check the bead twice a year. Catching a small crack or a lifting edge early means a quick spot repair instead of another full replacement.

If the caulk keeps failing in the same spot within months, something else may be going on — a tub that flexes when filled, a wall that has moved, or moisture coming from behind the tile. A handyman or tile pro can check whether the joint itself is the problem or just the symptom. A typical tub re-caulk runs $100 to $250 professionally, and a full shower re-caulk a bit more.

On ZIP Pros — "Pros in your ZIP" — describe the problem once and get free quotes from local handyman pros, with real starting prices shown up front. Mention whether it's a tub, shower, or sink joint and whether there's mold or water damage behind it — that tells the pro what the job involves.