How to Caulk a Bathtub

Preflight — supplies, ventilation, and a dry tub joint before you strip old caulk.

Silicone caulk · gun · tape · knife · alcohol · fan on · tub dry 24+ hr after last shower.

Silicone bonds only to clean dry surfaces — working over a damp joint or wrong caulk type fails within weeks.

1. Supplies gathered? Silicone caulk, gun, tape, removal tool, alcohol, rags, and gloves are ready.
2. Tub dry 24+ hours? No shower since yesterday — joint feels dry to the touch.
3. Fan on or window open? Ventilation reduces fumes during strip and cure.
4. Right caulk type? 100% silicone or tub-and-tile label — not acrylic latex.

Supplies are ready, the bathroom is ventilated, and the tub joint has been dry at least 24 hours since the last shower.

Silicone will not bond to a damp joint — new bead pulls away or traps mold under old residue. If you showered within 24 hours or the tissue test shows dampness, see Wet surface before taping. Use 100% silicone or tub-and-tile labeled caulk in wet zones — acrylic latex peels within weeks when shower water hits the joint daily.

Inspect the existing caulk bead for mold, gaps, and peeling.

Full joint run · mold · gaps · loose edges noted.

Knowing whether mold or grout failure hides under the bead tells you if the main path is enough or the mold branch is required first.

1. Stand at one end of the tub and scan the full tub-to-wall joint in good light.
2. Note black, green, or fuzzy spots, gaps where water could enter, and edges lifting away.
3. Press gently on loose sections — if caulk peels easily, the full strip path is confirmed.

You know whether mold, gaps, or peeling are present along the full joint run.

Black, green, or fuzzy mold on old caulk means the bead failed — do not caulk over it. See Moldy old caulk before stripping.

Score the old caulk bead on both sides with a utility knife.

Blade on tub side · blade on wall side · cut through bead only.

Scoring frees the old bead from tile and tub so stripping does not tear finish surfaces or leave hidden residue.

1. Hold the blade flat against the tub surface and cut along the bottom edge of the old bead.
2. Repeat on the wall-tile side, cutting along the top edge of the old bead.
3. Work in short 6-inch passes — do not dig the blade into acrylic or fiberglass.

Old caulk is scored on both tub and wall sides without scratching finish surfaces.

Do not scrape acrylic or fiberglass tubs with metal blades — use plastic removal tools and score gently so you do not gouge the tub surface.

Pry and strip old caulk with a removal tool or stiff putty knife.

Plastic tool · pry scored bead · all old material in trash.

Any old caulk left in the gap prevents the new bead from bonding and traps moisture that grows mold under the fresh line.

1. Hook a plastic caulk removal tool or putty knife under the scored bead and lift it out.
2. Pull the full length into the trash — do not drop strips into the tub drain.
3. Check the gap — no gray or discolored caulk should remain in the joint.

Old caulk is fully removed and the bare joint gap is visible along the full run.

Scrub the joint with isopropyl alcohol and dry completely.

Alcohol on rag · scrub gap · tissue test must read dry.

Soap film and shower residue block silicone adhesion — alcohol cuts grease and the tissue test confirms the joint is truly dry.

1. Soak a lint-free rag with isopropyl alcohol and scrub the full joint gap and 1 inch on each side.
2. Wipe with a dry rag, then press a fresh tissue against the joint for 10 seconds.
3. Tissue must come away dry — if it picks up moisture, stop and use the wet-surface branch.

Joint is free of soap film and a dry tissue pressed to the gap comes away with no damp mark.

Tissue shows damp or joint fogged after a recent shower? → Wet surface.

Apply painter's tape 1/8 inch from the joint on tub and wall sides.

Tape on tub lip · tape on wall tile · joint gap exposed.

Tape defines a clean bead edge — without it, silicone smears on tile and tub and leaves a ragged line that peels first.

1. Run painter's tape along the tub side about 1/8 inch below the joint gap.
2. Run a second tape line on the wall tile about 1/8 inch above the gap.
3. Press tape edges firmly so caulk cannot seep underneath during application.

Straight tape lines border the joint on tub and wall sides with the gap fully exposed.

Cut the silicone tube nozzle at 45 degrees to match bead width.

45-degree snip · opening matches gap · pierce foil seal.

A nozzle opening too wide lays a fat messy bead; too narrow leaves hollow pinholes that let water behind the tile.

1. Snip the nozzle tip at a 45-degree angle — start small; you can trim again if needed.
2. Match the opening width to the joint gap — usually 1/8 to 1/4 inch for tub joints.
3. Pierce the inner foil seal with the gun plunger rod or a stiff wire.

Nozzle is cut to match gap width and the inner seal is pierced so caulk can flow.

Load the tube in the caulk gun and squeeze until bead appears at the tip.

Tube seated in gun · plunger engaged · caulk at nozzle tip.

A tube not fully seated in the gun skips and leaves gaps in the bead — priming the tip confirms smooth flow before the joint pass.

1. Cut the tube base foil if present, then drop the tube into the caulk gun cradle.
2. Turn the plunger ratchet and push until the plunger plate contacts the tube bottom.
3. Squeeze the trigger slowly until a small bead appears at the nozzle tip, then wipe the excess.

Tube is loaded, plunger engaged, and caulk flows cleanly from the nozzle tip.

Apply a steady continuous bead along the tub-to-wall joint.

Even gun speed · fill gap fully · one pass where possible.

A bead that does not fully fill the gap leaves hollow channels — water travels behind tile through pinholes you cannot see from the surface.

1. Place the nozzle at the far end of the joint and squeeze as you pull the gun toward you.
2. Keep speed steady so the bead fills the gap without voids or thin spots.
3. Overlap the start and end slightly if you must pause — you will smooth joins in the next step.

A continuous bead runs the full tub-to-wall joint with no large voids or bare gaps.

Fresh bead pulls away or will not stick to the surface? → Wet surface.

Smooth the bead with a wet finger or caulk finishing tool.

Concave profile · one light pass · no smears outside tape.

Tooling sets the concave profile that flexes with tub movement — an untooled bead is too proud and peels at the edges first.

1. Dip a finger in soapy water or use a caulk finishing tool at a shallow angle.
2. Draw along the bead in one light pass to form a concave profile.
3. Wipe any smears on tape immediately with a dry rag — do not spread caulk onto tile.

Bead has an even concave profile with no drag marks or smears on tub or tile.

Peel tape outward at 45 degrees while the bead is still wet.

Pull away from joint · 45-degree angle · before skin forms.

Tape pulled after the bead skins tears the edge — peeling while wet leaves a crisp line that resists peeling in shower use.

1. Start at one end and pull tape away from the joint at a 45-degree angle.
2. Peel the tub-side tape first, then the wall-side tape in the same direction.
3. Do not drag tape through the wet bead — lift outward in one smooth motion.

Tape is off both sides and bead edges are clean with no caulk bridges across the tape lines.

Let cure 24 hours undisturbed and keep the area dry.

No shower 24 hr · fan running · do not touch bead.

Silicone reaches full waterproof strength only after the full cure window — shower use too early washes uncured caulk away or softens the profile.

1. Keep the bathroom fan running or the window cracked for the full cure period.
2. Do not shower or splash the joint for at least 24 hours.
3. Avoid touching or wiping the bead — it should feel firm and rubbery when cure is complete.

Joint stayed dry for 24 hours and the bead feels firm and rubbery to a light touch.

Inspect for gaps or thin spots and touch up if needed.

Full run check · pinholes · thin areas filled.

A single pinhole or thin stretch lets water behind tile — a quick touch-up now prevents a full redo in a few months.

1. Scan the full joint in bright light for pinholes, thin spots, or missed sections.
2. Apply a small fresh bead to any gaps and smooth with a wet finger.
3. Allow touch-up areas the same 24-hour cure before using the shower.

Continuous seal runs the full joint length with no visible gaps or thin spots.