How to Caulk a Bathtub: Removing Old Sealant and Laying a Clean Bead

To caulk a bathtub, cut out every trace of the old sealant, clean the joint with a degreasing cleaner and then rubbing alcohol, and let it dry completely. Fill the tub with water so it sits at its lowest position, mask both sides of the joint with tape, and run one continuous bead of bathroom-grade silicone along the gap. Smooth it in a single pass, peel the tape straight away and leave the sealant to cure for as long as the tube says before anyone showers. Most of the effort goes into the preparation; the bead itself takes only a few minutes.

When a tub needs new caulk

Sealant around a bath does not last forever. Look for these signs:

• Black or grey spots of mould that will not scrub off, because they are growing inside the sealant.
• Edges that lift, peel or can be pulled away with a fingernail.
• Cracks or gaps, especially at the corners.
• Damp patches, stains or loose tiles near the tub, or a mark on the ceiling below the bathroom.

The last group matters most. Water creeping behind a failed seal can soak into the wall, the subfloor or the ceiling underneath long before you see it. If there is already staining downstairs or a soft spot in the floor, it is worth having the area checked rather than simply sealing over the top; the warning signs listed in our piece on the benefits of regular plumbing checks are a useful guide to when a professional should look first.

What you need

Silicone and acrylic-based caulks behave differently. Silicone stays flexible and copes well with constant moisture, which is why it is the usual choice around baths. Acrylic versions are easier to tool and can be painted, but are generally better suited to drier joints. Whatever you choose, follow the manufacturer's directions on ventilation and drying time.

Step by step

1. Remove the old sealant

Slice along both edges of the old bead with a utility knife, holding the blade low so you do not scratch the tub or the tiles. Then pull and scrape it out. Stubborn sections loosen if you apply a caulk remover and wait. Take your time here; new silicone does not stick to old silicone, so any leftover film will spoil the result.

2. Clean and dry the joint

Scrub the gap with a bathroom cleaner to remove soap scum, rinse, then wipe with rubbing alcohol to lift the last residue. If there is mould deep in the joint, treat it with a suitable mould cleaner and rinse well. Now let everything dry. Leaving the bathroom ventilated overnight is the simplest way to be sure; trapped moisture is the most common reason a new bead fails.

3. Fill the tub

A bath full of water sits slightly lower than an empty one, which opens the joint to its widest point. Sealing it in that position means the bead is squeezed rather than stretched when someone climbs in later. Leave the water in until the sealant has skinned over.

4. Tape the edges

Run tape along the tub and along the wall, leaving a gap just wider than the joint. Press it down firmly so sealant cannot creep underneath.

5. Lay the bead

Cut the nozzle at an angle, starting with a small opening; you can always cut more. Hold the gun at a steady angle and push the bead along the joint in one smooth movement, starting in a corner and working towards the next. Keep the pressure even and avoid stopping halfway along a side if you can.

6. Smooth and peel

Run a smoothing tool or a gloved, slightly damp finger along the bead once, pressing it into the gap and leaving a gentle concave curve. Then peel the tape away straight away, pulling it back on itself and away from the joint. Waiting until the sealant skins over makes the edges tear.

7. Let it cure

Drain the tub only once the surface has firmed up, and keep the bath and shower out of use for the full curing time printed on the tube. Silicone usually needs considerably longer to cure through than to feel dry on top.

Mistakes that shorten the life of the seal

• Sealing over old caulk instead of removing it.
• Working on a joint that is still damp, or in a steamy room.
• Laying too much sealant, which smears and traps air.
• Going over the bead repeatedly with a finger, which drags it out of shape.
• Running a shower the same evening.

Once it is done, a new seal stays clean for longer if the bathroom is aired after every bath or shower and the joint is wiped dry now and then. A quick glance along the tub edge fits easily into a weekly Sunday reset, and spotting a lifting corner early saves a bigger repair later. If the weekend still has room in it and the weather is kind, outdoor wood needs similar care; the prep-first approach in our guide to staining a deck follows the same idea of cleaning thoroughly before anything new goes on.