How to Caulk a Bathtub or Shower

A clean bead of caulk is the only thing standing between your shower spray and the wall cavity behind it. Get it wrong and water wicks into drywall and framing for months before you see the stain — by then you’re looking at mold remediation and a rotted subfloor, not a $12 tube of sealant.

What you’ll need

• 100% silicone caulk — kitchen & bath / mildew-resistant (DAP, GE, or Gorilla); avoid acrylic-latex for wet areas
• A dripless caulk gun — found alongside the caulk; a ratchet-rod gun gives you clean starts and stops
• Caulk remover / softener gel — softens stubborn old silicone so it peels instead of shredding
• A sharp utility knife — to score both edges of the old bead
• A putty knife or plastic scraper — to lift the softened caulk without gouging the tub
• Painter’s tape — two lines that frame the joint for a razor-straight bead
• Rubbing alcohol or a degreaser — the final wipe so silicone actually bonds
• A bathroom cleaner — to strip soap scum before you seal
• Mildew remover / bleach gel — kill any black spots hiding in the joint first
• Sponges and rags, plus disposable gloves — for cleanup and to keep uncured silicone off your skin

Step 1: Strip out every bit of the old caulk

Run your utility knife down both edges of the existing bead — where it meets the tub and where it meets the wall — then pull the strip free. For silicone that won’t budge, lay on a caulk-remover gel, wait the label time, and it will scrape off in ribbons with a plastic putty knife.

Common mistake: new caulk will not stick to old caulk. If you leave even a thin film of the previous bead, the new one lifts within weeks. Get the joint down to bare tile and tub.

Step 2: Kill the mildew and clean the joint

Any black speckling in the corner is mildew, and it will grow right through fresh caulk. Treat it with a mildew remover or bleach gel, let it dwell, and rinse. Then scrub the whole area with a bathroom cleaner to cut soap scum and body oils that block adhesion.

Step 3: Dry it completely, then wipe with alcohol

Silicone hates moisture during application. Towel the joint, then leave the fan on or the window open for a few hours — overnight is better. Just before caulking, give the surface a final pass with rubbing alcohol from your cleaning supplies on a lint-free rag. This flashes off fast and removes the last invisible residue.

Pro tip: fill the tub with water before you caulk the tub-to-wall joint. The weight pulls the tub down to its lowest position; caulking it empty means the joint stretches and cracks the first time someone takes a bath.

Step 4: Tape both sides of the joint

Press a line of painter’s tape onto the tub and another onto the wall, leaving a gap the width you want your finished bead — usually about 3/16″. This is the difference between a hand-tooled look and a factory-clean line, and it takes five minutes.

Step 5: Cut the tip and lay one continuous bead

Snip the nozzle at a 45-degree angle to match your gap, load the tube in the gun, and squeeze a test bead onto cardboard. Then run the gun steadily along the joint, pushing (not pulling) the tip ahead of the bead so it packs silicone into the gap. Work one wall or edge at a time so nothing skins over before you tool it.

Step 6: Tool the bead and pull the tape

Wet a gloved fingertip (a dab of dish soap in water keeps silicone from grabbing) and draw it smoothly along the bead once — one pass, light pressure. This forces caulk into the joint and leaves a concave, water-shedding surface. Immediately pull both tape lines up and away while the caulk is still wet, then leave it alone.

Don’t rush the cure: keep the shower dry for a full 24 hours (check your tube — some need 48). Water on uncured silicone leaves a cloudy, weak seal you’ll be redoing next month.

Frequently asked questions

Reseal your tub right and it stays watertight for years — skip the prep and you’ll be back at it before summer. If you hit a stubborn joint or want a caulk brand matched to your exact surround, your local independent hardware store can hand you the right tube today, or you can ask us here.