How to Recaulk a Bathtub or Shower Joint

Job: replace a failed tub or shower bead — from clean, dry, bondable substrate to a cured, watertight, mildew-resistant joint that survives the tub being filled a thousand times.

Time: about an hour of gunning and tooling for a standard three-wall tub perimeter — after the removal (its own guide: 1–2 hours plus overnight drying).

Difficulty: neatness and restraint, not strength. Two disciplines decide the whole job: fill the tub before you caulk, and tool each section once, while it's fresh.

Everything else: the cartridge of sealant itself — this store sells the gun and the finishing tool, not the chemistry; buy a tube labeled for tub-and-shower use — plus painter's tape if you want guided edges, isopropyl or mineral spirits and clean rags, nitrile gloves, a spray bottle of soapy water for silicone tooling, and a utility knife and a long nail: none of the three guns above claims a spout cutter or a seal punch, so the cut and the puncture come from the 43660's tube cutter and the junk drawer — which is exactly the corner the homeowner tier's price cuts.

Before you start: the admission ticket, and the rule that decides everything

Arrive at clean, dry, bondable substrate — or go back one guide. The removal is not part of this page; it is its own complete walkthrough (remove-old-caulk), and its exit test is this page's entrance exam: mist the joint with water — droplets *beading* along the line mean silicone film remains, and the new bead will peel; water *sheeting* plus a dry fingertip finding no slick spot means the joint is bondable. New caulk over old caulk residue fails the way paint over grease fails, and no gunning technique on this page can rescue a joint that flunks the mist test. One more clock to respect: a stripped joint stays clean for a day, not a month. Recaulk promptly, or dust and soap film start rebuilding the contamination you just removed.

Be honest about what was living behind the old bead. A tub bead rarely fails dry: it fails because water got behind it, which means the substrate under the old caulk has been damp — and usually colonized — for months. The kill belongs to the removal guide (1:10 bleach solution or an EPA-registered mildewcide, rinsed with clean water), and so does the dry-out: hours to overnight with a fan, because *surface-dry is not dry*, and sealant will not bond to substrate that is still exhaling moisture. If you skipped that step, do it now and accept losing the day — caulking over a damp joint is the single most common way this job fails, and caulking over a live colony guarantees black shadows through the new bead within weeks. Two boundaries while you're at it: bleach in a small enclosed shower needs ventilation and must never meet ammonia- or acid-based cleaners — the mix makes chloramine or chlorine gas, and a shower stall is exactly the small, poorly ventilated space where it accumulates. And if mold runs *behind* the tile rather than sitting on the joint faces, caulk is cosmetics — that wall is a regrout or tile repair, not a bead.

FILL THE TUB. This is the step that separates beads that last from beads that split by spring. A tub-to-wall joint is a movement joint: the tub sinks under load — the caulking line's reasoning doc puts it at a few millimeters under 300 pounds of water and bather, and modern acrylic and fiberglass units flex the most. Caulk an empty tub and the bead cures with the joint closed; then every single fill stretches it in tension, hundreds of times a year, until it tears free or splits down the middle — which is the whole reason tub beads fail on a schedule. Fill the tub before you caulk and the geometry inverts: the bead cures with the joint at maximum open, so for the rest of its life the joint can only close on it, and the cured sealant works in compression — the state every sealant tolerates far better than stretch. So: after prep, before gunning, fill the tub to its working level. Wipe any splash off the joint and let it flash dry — the substrate must stay bone dry even while the tub is full. Leave the water in until the sealant has cured, then drain. Cast-iron tubs move least and glass-fiber units most, but the rule costs nothing and pays everywhere; a shower stall with no tub simply skips it (a shower pan still moves — keep the pan-to-wall bead properly sized and tooled, and it lives in compression's cousin: small, well-bonded movement).

Choose the chemistry with both eyes open — the label is a contract. The tub aisle offers two honest choices. 100% silicone, labeled tub-and-shower: waterproof, permanently flexible, the best movement tolerance in the aisle — the specialist for a loaded, daily-flooded joint — and it exacts three prices: paint will never stick to it, cleanup is solvent rather than water, and nothing (including fresh silicone) bonds well where silicone has been, so the joint is committed to silicone for life. Siliconized acrylic / kitchen-and-bath acrylic with mildewcide (the 09968's class): paintable, water cleanup, noticeably easier for a first-timer to tool — and it gives back some movement capability and some lifespan in a joint that gets soaked every day. The honest steer for a tub perimeter proper is silicone: the fill-the-tub physics above is a movement argument, and movement is silicone's specialty. Run the acrylic where the bead must take paint — say, where a surround meets painted drywall — or end the silicone exactly where the paint begins. Either way, buy a wet-area formula (mildew-resistant, labeled for tub and shower), match the color to the fixture (white, almond, or clear), and read the cure line on the tube like it's load-bearing, because it is: "water-ready" commonly means 24 hours, full cure runs days, not hours, and water-ready is not cured.

The recaulk

Load and prep the gun — the one-paragraph version of a ritual with its own guide. Cut the nozzle small and at roughly 45° — at the tip first, because every millimeter lower is a permanently bigger bead; a hole about half the gap's width, moved slowly, beats a big hole moved fast in every case that will ever matter. The 43660's tube cutter or a utility knife makes the cut; none of these three guns claims a cutter on the frame. Puncture the inner foil seal with a long nail or stiff wire — skip it and trigger pressure has nowhere to go until something gives, usually backwards. Seat the cartridge, advance the rod to contact, and run a test bead on cardboard until the size looks like the joint. The full ceremony — seal types, rod handling, pressure setting — is the load-and-prep-a-caulk-cartridge guide. If you want guided edges, run two parallel lines of painter's tape leaving an even reveal about the finished bead's width: honest trade-off stated plainly — tape buys a beginner dead-straight lines and costs a slightly proud edge where the caulk steps off the tape; a practiced hand skips it.

Run the bead — one section at a time, at the speed of your best attention. Work one joint face per pass: the back wall first, then each side wall, finishing at the front. Bead uniformity comes from travel speed, not trigger squeeze: set a working pressure and keep the nozzle moving at constant speed, topping up with the trigger in rhythm — when the bead fattens, speed up; when it starves, slow down; never chase it with the trigger. Treat every plane change as a full stop: end the bead at the inside corner, release the pressure, and restart on the next face — swinging the nozzle around a corner mid-bead is how corners get buried. And at *every* stop, release the pressure before lifting the nozzle — thumb lever on the 46400, rod release on the 46410, and on the 46310 the StopDrip does the un-drooling for you; that claimed behavior, ratchet advance without the ooze after trigger release, is the entire reason that gun exists. Section length is set by your tooling window, not your ambition: gun what you can tool while it's fresh — one wall at a time is right for a first-timer.

Tool it — once, firmly, within the skin time. Every sealant skins — acrylics within minutes, silicone faster than beginners expect — and the tooling pass has to land inside that window, which is why the rhythm of this job is *gun, tool, move on*. One steady pass per section with the 43660's padded end: it presses the caulk into both joint faces (that pressed contact — the wetted bond — is what the bead's life hangs on, not looks), sets a consistent concave profile, and carries the excess away; wipe the tool clean after every stroke. The honest alternative is as old as caulk: a wetted fingertip — plain water for acrylic, soapy water for silicone so it won't grab — tools a bead adequately and always has. What the padded end adds is a radius your finger doesn't have, no solvent on skin, and a working edge in the vertical-to-horizontal transitions at the tub corners, where a fingertip flattens the profile. If you taped, pull the tape *now*, low and away from the bead while everything is wet, then lay one feather-light finishing touch on the tape line. Do not go back and re-polish half-set caulk — a second pass through a skinning bead drags and wrinkles what a single pass left sealed. The full technique — profiles, corners, tool care — is the tool-and-smooth-a-caulk-bead guide.

Cure discipline — the cheapest step to respect and the most expensive to skip. Leave the water in the tub until the label's cure time has passed, then drain gently; the joint settles into its compressed working state with the bead already set. No spray, no shower, no cleaning products on the bead until at least the label's water-ready time — and remember what that phrase bought: water-ready means a light rinse won't wash it away, not that the chemistry is done. Full cure runs days; if the household can spare the tub a second night, give it the night. A bead that cost an hour deserves 48 patient hours more than it deserves a season-one redo.

Drain, inspect, and close the loop. With the tub empty, sight down the bead line in raking light: continuous, concave, no pinholes, no skips at the corners, no spots where the bead sits on top of the joint instead of in it. A pinhole found today is a ten-minute dab; found in six months, it's this whole job again. Then the honest maintenance sentence: every tub bead is a wear item. Ventilation after showers and an occasional rinse slow the mildew clock; nothing stops the movement clock. When this bead eventually fails — years from now if the tub was full when you gunned it — the removal guide is waiting, and the loop runs again.

What goes wrong (and the fix)

"The new bead peeled off within weeks." Wet or contaminated substrate — almost always a skipped mist test over invisible silicone film, or caulk over a damp joint. Strip it (it comes easily; it never bonded), rerun the removal guide's clean-to-bond step, and re-bead dry.

"Black mildew is showing through the bead already." It was caulked over a live colony or onto damp substrate, or the tube wasn't a wet-area formula. There is no bleaching this away permanently — strip, kill, rinse, dry overnight, and re-bead with a tub-and-shower-rated sealant.

"The bead split/cracked along the tub by next season." The signature failure: the tub was empty when it was caulked. The bead cured at joint-closed, then every fill stretched it. Strip and redo it with the tub full — this time the joint can only compress it.

"It skinned over before I tooled it." Sections too long, or a hot dry room shortening the skin time. Never drag the tool through a skinned bead — it tears and wrinkles instead of smoothing. Let the section cure, slice it out, and redo it shorter; from now on: gun one wall, tool one wall.

"The gun keeps oozing between sections." Stored pressure — the ratchet's signature. Release the rod at every stop, the instant the bead ends; the 46400's thumb lever dumps pressure fastest, and ending the ooze is the 46310 StopDrip's entire job description.

"The bead sank into the gap." The joint is deeper than it is wide and the bead has no back to press against. Backer rod first, then caulk — the sizing and the two-surface rule live in the seal-a-movement-joint-with-backer-rod guide.

The history footnote (because these pages should be worth reading)

The joint this guide seals is younger than it looks. A quarter-ton of enameled iron barely moves when you fill it, and its era's tubs were sealed accordingly. What made the tub-to-wall joint a *movement* joint in nearly every house was the postwar shift to light, flexy acrylic and fiberglass tubs and surrounds — the fill-the-tub rule on this page is the trade's answer to tubs that weigh a tenth of Kohler's and sag under every bath.

Related walkthroughs: load-and-prep-a-caulk-cartridge · tool-and-smooth-a-caulk-bead · seal-a-movement-joint-with-backer-rod · repair-caulk-without-a-gun (the no-gun touch-up path) · caulk-a-kitchen-backsplash-or-sink-rim. Every linked PDP lists this guide under its applications — the graph runs both directions.