How to Re-Caulk a Bathtub or Shower

Caulk is not decoration. It is the seal that keeps shower water from getting behind the tub and into the wall. When it turns black, peels or cracks, it has stopped doing its job, and replacing it is one of the cheapest ways to prevent a much bigger repair. The work is simple. What makes it last is the prep.

Before you start

You need good ventilation, because caulk gives off fumes as it cures. Open a window or run the fan. Read the tube, since drying times and rules differ by product.

Step 1: Take out every bit of the old caulk

1. Cut along both edges of the old bead with the utility knife, so it lifts off cleanly.
2. Pull and scrape it out with a caulk remover or plastic scraper. Avoid a metal scraper on a fiberglass or acrylic tub, because it scratches.
3. Get all of it. New caulk will not stick to old caulk, and a thin film left behind is why many re-caulk jobs peel after a few months.

Step 2: Clean and dry the joint

4. Scrub the joint with a mildew cleaner and a brush to kill the mold that is living in the gap.
5. Wipe it with rubbing alcohol to remove soap film and residue.
6. Let it dry completely. Wait a few hours or overnight. Caulk applied to a damp surface will not bond, and trapping moisture inside is how mold comes back.

Step 3: Fill the tub before you caulk

7. Fill the tub with water about as full as you ever use it. The weight pushes the tub down and opens the gap to its widest. If you caulk an empty tub, the caulk gets squeezed and cracks when the tub is full. Leave the water in until the caulk has cured.

Step 4: Apply the bead

8. Tape both sides of the joint with painter's tape, leaving a gap about an eighth of an inch wide, so you get a clean line.
9. Cut the tip of the tube at a 45 degree angle, making a small opening. You can always cut more.
10. Run one continuous bead along the joint, moving steadily and pushing the caulk into the gap rather than piling it on top. Do the whole joint without stopping if you can.
11. Smooth it with a gloved finger or a smoothing tool dipped in soapy water, pressing it into the gap in one pass.
12. Pull off the tape right away, while the caulk is wet, in one slow motion.

Step 5: Let it cure

Do not touch the new bead, and do not drain the tub or use the shower until the time on the label has passed, usually 24 hours.

Common mistakes

• Caulking over mold or old caulk. It will fail quickly.
• A bead that is too big. A thin, neat bead seals better than a thick one.
• Using the wrong product. Caulk for painting and general use is not made for constant water.
• Going back for touch-ups on wet caulk. Leave it alone, or you will make it worse.

When it is not a caulk problem

A bead that keeps failing in the same spot, or a wall that feels soft near the tub, is telling you water is getting through somewhere else. See the list below.