How to Caulk a Bathtub

Updated August 2026 · Home Project Resources

Remove all of the old caulk first. Not most of it, all of it, right down to bare tub and bare wall. New caulk laid over old caulk fails every single time, and that one shortcut is why most re-caulk jobs look cracked, gray, and peeling within a year.

After the joint is stripped, clean it, kill any mold living in it, dry it completely, then pull one continuous bead of 100 percent silicone. Total working time is about 60 to 90 minutes, the materials are among the cheapest in the store, and a joint done this way lasts 5 to 10 years instead of 8 months.

Planning more than a caulk line? If the tub surround tile is coming out too, get your exact material count with our free tile calculator, and the bathroom remodel cost guide breaks out fixtures and labor so you can see whether re-caulking buys you three more years or just delays the inevitable.

Updated August 2026

A note on numbers. This page gives you dimensions, quantities and scope, not dollar figures. Material and contractor pricing varies by region, by season and by the specifics of your job, and we do not set any of it. Work out what you need here, then get quotes that can be compared to each other.

How to caulk a bathtub: the whole job in seven steps

Here's the sequence before the detail. Do them in this order, because every one of them depends on the one before it.

1. Strip all the old caulk down to bare tub and bare wall.
2. Clean the joint and kill any mold living in it.
3. Dry the joint completely. Silicone will not bond to damp.
4. Fill the tub with water so the joint is at its widest while the caulk cures.
5. Cut the nozzle small, at 45 degrees, and load a smooth-rod gun.
6. Pull one continuous bead and tool it within 5 minutes.
7. Wait out the full cure before the tub gets used or drained.

The whole thing is 60 to 90 minutes of work plus 24 to 72 hours of waiting.

Why new caulk over old caulk always fails

Caulk sticks to clean, dry, non-porous surfaces. It does not stick to cured silicone, and it does not stick to soap film, mildew, or the powdery residue old acrylic caulk leaves behind.

When you squeeze a fresh bead over an old one, you get adhesion in maybe two places along the whole run. Everywhere else you have a thin skin of new caulk bridging a gap with nothing holding it down. The tub flexes when you fill it, the bead tears loose at the weakest point, and water goes straight into the wall through a joint that looks sealed from the outside.

That hidden water is the expensive part. A failing tub joint feeds the bottom course of drywall or backer board, and by the time you see a soft spot or a stain on the ceiling below, you're not buying a tube of silicone anymore. You're buying wall repair, which costs orders of magnitude more. If you've already got soft drywall near the tub, how to patch drywall covers cutting back to solid material before you re-seal anything.

What you need

The whole list is inexpensive, and only the first line is a true consumable. The caulk gun is the biggest single item and it is a one-time purchase, so a first-time job costs several times what a repeat job costs. A repeat job costs you a tube.

Step 1: strip every bit of the old caulk

Give this step the most time. It's 70 percent of the job and it's the part that decides whether the new bead lasts.

1. Score both edges. Run a sharp utility knife along the top edge where caulk meets the wall or tile, and the bottom edge where it meets the tub. You're cutting the bond, not gouging the surface. Keep the blade almost flat.
2. Apply softener if the old caulk is silicone. Silicone remover gel sits on the bead for 2 to 3 hours (check the label, some want overnight) and turns it into something you can pull off in ribbons rather than chips. Acrylic caulk usually comes out dry without help.
3. Pull the bead out with a plastic caulk removal tool. The hooked plastic blades are inexpensive and are shaped to ride in the corner. Work in one direction and try to lift a continuous strip.
4. Scrape the residue. There will be a thin film left behind, especially on tile grout. A plastic razor blade held at a low angle takes it off without scratching.
5. Check with your fingernail. Run it along the joint. If you feel any ridge or rubbery patch, it's still there. Keep going.

Why a metal razor blade on an acrylic tub is a mistake

Acrylic and fiberglass tubs are soft. A steel razor blade will cut fine scratches into the surface in seconds, and once the gloss layer is scored, the scratches hold soap scum, go dull and gray, and never buff back out. On a tub that costs several hundred times what the tube of caulk does, that's a permanent cosmetic loss for the sake of saving 10 minutes.

Use plastic blades on acrylic, fiberglass, and cultured marble. A metal blade is acceptable on glazed ceramic tile and on porcelain-on-steel or cast iron tubs, held at a very low angle, but the plastic tool works there too. When in doubt, plastic.

Step 2: clean the joint and kill the mold

Stripping the caulk usually exposes black staining in the corner. That's mold, and it's alive. If you seal over living mold, it keeps growing under the new silicone and shows through as dark shadows in a few months. The caulk isn't failing at that point, it's just transparent enough to show what you trapped.

1. Scrub the joint with a stiff brush and bathroom cleaner to remove soap scum and body oils. Soap film is a bond breaker.
2. Kill the mold. A solution of 1 part household bleach to 3 parts water, applied to the bare joint and left for 10 to 15 minutes, does it. A commercial mold and mildew remover works too. Ventilate the room, wear gloves and eye protection, and never mix bleach with any ammonia-based cleaner.
3. Rinse thoroughly with clean water. Bleach residue interferes with silicone adhesion.
4. Wipe with denatured or isopropyl alcohol. This pulls off the last of the oils and residue and evaporates clean.
5. Dry completely. This is not optional. Silicone will skin over trapped moisture and release later.

How dry is dry enough

Give the joint at least 24 hours with no showering, or speed it up with a hair dryer on low followed by 2 to 3 hours of a fan pointed at the corner. If the tub joint has been leaking, the gap may have water sitting behind the tub flange, and that takes longer. A dehumidifier in the room overnight is the reliable move.

One warning for older bathrooms. If the tub surround is painted plaster or painted drywall in a home built before 1978, assume the paint contains lead until a test says otherwise. Do not sand or scrape painted surfaces. Scoring caulk with a knife is fine; taking a sander to the wall above the tub is not. In homes built before 1990, sheet vinyl flooring, old floor tile, and pipe wrap around the tub supply lines can contain asbestos. Do not cut or tear any of it. Get it tested and let a certified abatement contractor handle removal.

Step 3: fill the tub with water before you caulk

This is the trick almost nobody has heard of, and it's the difference between a bead that lasts five years and one that splits in six weeks.

Fill the tub with water to a few inches below the overflow, or get in and stand in it, before you apply the caulk. Then leave it full until the caulk has cured.

Here's why. An empty acrylic or fiberglass tub sits high. Add a person plus 40 gallons of water, roughly 500 pounds, and the tub deflects downward. It might only move 1/16 to 1/8 of an inch, but the caulk joint is only 1/8 to 1/4 inch wide, so that movement is a huge percentage of the bead.

Caulk applied to an empty tub is cured at its narrowest. Every time you get in, the joint stretches past what the bead can take, and it tears at the top edge. Caulk applied to a loaded tub cures at its widest, so all subsequent movement is compression, which silicone handles easily.

Worked example. A 60 by 30 inch acrylic tub holds about 42 gallons filled to the overflow. Water weighs 8.34 pounds per gallon, so that's roughly 350 pounds, plus a 170 pound person is 520 pounds on a tub whose empty weight is around 70 pounds. On a flexible acrylic shell over a mortar-poor base, deflection of 1/16 to 1/8 inch is normal. On a cast iron tub sitting on a solid floor, deflection is near zero and this step matters much less. If you don't know which you have, tap the side. A dull thud is cast iron or steel, a lighter hollow sound is acrylic or fiberglass. Fill it either way, it costs you nothing.

Drain the tub only after the full cure time on the tube has passed.

Step 4: pick the right caulk

Say it plainly: 100 percent silicone is the right choice for a bathtub joint, and it cannot be painted. Not "poorly," not "with the right primer." Paint will bead up, flake, and peel off silicone. If you need the joint to match painted trim, use a hybrid MS polymer or siliconized acrylic and accept the shorter life, or paint the wall first and caulk last.

Buy a tube labeled kitchen and bath, or tub and tile, with mildewcide. Skip generic construction silicone, which often has no mildewcide and can carry an acetic (vinegar smell) cure that's harsher on some surfaces.

Step 5: cut the nozzle and load the gun

1. Cut the nozzle at a 45 degree angle, near the tip, so the opening is about 1/8 to 3/16 inch across. Cut small first. You can always cut more, you can't uncut.
2. Match the opening to the gap. A 1/8 inch gap wants a 1/8 inch opening. A wide, uneven gap wants closer to 1/4 inch. Too big an opening is the number one cause of a messy job.
3. Puncture the inner seal. Most guns have a wire for this. Push it in until it pops.
4. Use a smooth-rod gun with a drip stop. A ratchet gun keeps pushing after you release the trigger and dumps caulk where you don't want it.
5. Tape if you want crisp lines. Run painter's tape on the tub and on the wall, leaving a gap about 3/16 inch wider than your intended bead. Pull the tape while the caulk is still wet, within 5 minutes, at a shallow angle away from the bead.

Step 6: pull one continuous bead

Push or pull, both work, but pulling gives you a better view of the joint and a more consistent bead for most people.

1. Start in a corner and work toward an end so you don't have to stop mid-run.
2. Hold the nozzle at roughly 45 degrees to the joint, tip touching the back of the corner.
3. Move at a steady speed with steady trigger pressure. Consistency beats speed. If you go too slowly, you overfill. Too fast and the bead breaks and leaves voids.
4. Do the whole run in one pass if you can. Every stop and start is a potential weak point. On a 60 inch tub, do the long back wall in one pull, then each short end wall in one pull.
5. Don't overfill. The bead should sit in the joint, not sit on top of it like a rope.

Tooling the joint

Tooling isn't just cosmetic. It's what presses the caulk into the joint and forces contact with both surfaces. An untooled bead touches the corners only lightly and peels away later.

Within about 5 minutes of laying the bead, before it skins:

• Wet your finger with soapy water or denatured alcohol, or use a caulk finishing tool.
• Draw it along the bead in one smooth stroke with light, even pressure.
• Wipe the excess off your finger onto a paper towel after each pass, so you don't drag globs back into the joint.
• One pass, maybe two. Working it repeatedly drags it thin and breaks the seal at the edges.

A finishing tool with the right radius gives a more consistent result than a finger on long runs. Both are fine. What matters is that the caulk is pressed in, not smeared over.

Step 7: cure time before you use the tub

Skin time and cure time are different numbers, and people confuse them constantly.

Read your specific tube. Fast-cure silicones exist that are water-ready in 3 to 12 hours. Standard neutral-cure silicone in a cool, dry room can take the full 72 hours.

The practical rule: do this on a Friday evening and use the tub Sunday morning. Keep the tub full of water the entire time, run the bathroom fan, and don't shower in there. A bead that gets wet at hour 6 is a bead you'll be redoing.

The mistakes that ruin a good caulk job

Using way too much caulk. A fat bead does not seal better. It skins over on the outside while staying uncured underneath, it collects soap scum in the wide flat face, and it looks like a repair rather than a detail. If the gap genuinely is wider than 1/4 inch, pack it with foam backer rod first and caulk over that, or fix whatever is causing the gap.

Caulking joints that shouldn't be caulked. Not every seam in a bathroom is a caulk joint. Tile to tile seams are grout, not caulk. Filling a cracked grout line with silicone traps moisture in the tile bed and makes the problem worse. Change-of-plane joints (wall to wall, wall to tub, wall to floor) get caulk. Flat field joints get grout.

Sealing a joint that needs to drain. This one causes real damage. The weep holes at the bottom track of a sliding shower door, and the gap under a tub spout escutcheon, exist so water that gets behind the assembly can get back out. Caulk them shut and that water has nowhere to go but into the wall. On a shower door track, caulk the outside of the track where it meets the tub deck, and leave the weep holes on the inside open. Same principle at the bottom of a tile shower curb.

Caulking over a moving joint that's actually a structural problem. If the gap between tub and wall grew from 1/8 inch to 1/2 inch, the tub is settling or the framing moved. Caulk won't hold that. Find out why first.

Not letting it dry after the removal step. Alcohol wipe, then patience. Silicone will not bond to a damp surface, and you won't be able to tell until it lets go.

What this costs, DIY versus hired

The pattern is the same everywhere: on the hired version, materials are almost a rounding error and labor is the whole number. Regional labor rates swing that by a wide margin in either direction, and most handymen have a minimum service call, so a lone caulk job is charged as a visit rather than as work. If you are hiring, bundle it with the other small jobs on your list in one visit, ask each quote to state the minimum call and whether it includes removal of the old bead, and get it in writing before you budget. If you're pricing a full tub-to-shower conversion instead, shower installation cost has the current numbers.

When to call a pro

Caulking is genuinely a DIY job. Call someone when:

• The wall behind the tub is soft, spongy, or stained. That's water damage, and caulk over rot is a cosmetic lie. The wall needs opening up.
• The tub moves when you step in it. An unsupported tub needs shimming or a mortar bed, and no bead survives that motion.
• Tile is loose or hollow-sounding around the joint. The setting bed has failed.
• You keep re-caulking the same corner every year. Something structural is moving, and a pro should find it.

Permits don't apply to caulking. They do apply to moving plumbing, replacing a tub with a different drain location, or opening walls in many jurisdictions. Check with your local building department before any of that.

Frequently asked questions

Do I really have to remove all the old caulk?

Yes. Silicone doesn't bond to cured silicone, and acrylic caulk leaves a chalky residue that acts as a release layer. A partial removal gives you a bead that's stuck in a few places and floating everywhere else. It will look fine for a month and fail by the end of the year.

What is the best caulk for a bathtub?

A 100 percent silicone labeled for kitchen and bath, with mildewcide. It stays flexible, is completely waterproof, and lasts 5 to 10 years in a wet joint. The tradeoff is that it can't be painted and it's less forgiving to tool. Siliconized acrylic is easier to work with but has half the life in a tub joint.

Should I fill the bathtub with water before caulking?

Yes, on any acrylic, fiberglass, or steel tub. A full tub deflects downward under the weight, so the joint is at its widest while the caulk cures. Every use after that compresses the bead instead of stretching it, which is what silicone handles best. Leave the water in until the caulk has fully cured.

How long before I can shower after caulking a tub?

Give 100 percent silicone at least 24 hours before water contact and 48 to 72 hours for a full cure. Fast-cure formulas can be water-ready in 3 to 12 hours, but check your tube. Getting the bead wet early is the most common way a good caulk job goes bad.

How do I stop mold from coming back in the caulk?

Kill it before you seal, with a bleach solution or mold remover left on the bare joint for 10 to 15 minutes, then rinse and dry. Use a caulk with mildewcide, run the bathroom fan for 20 minutes after every shower, and squeegee the tub walls. Mold in caulk is almost always a ventilation problem wearing a caulk costume.

Can I paint over silicone caulk?

No. Paint won't adhere to cured silicone. It beads up, dries in patches, and flakes off within weeks. If the joint must be painted, use a paintable siliconized acrylic or a hybrid MS polymer instead, and expect a shorter service life in a wet area. Paint the walls first, caulk last.

Why does my tub caulk keep cracking at the top edge?

Two usual causes. The bead was applied to an empty tub, so it cures narrow and then gets stretched every time the tub loads. Or the bead was never tooled, so it only lightly touches the wall and peels at that contact line. Filling the tub and pressing the bead in with a firm tooling pass fixes both.

What's the difference between caulk and grout around a tub?

Grout is a rigid cement product for flat joints between tiles in the same plane. Caulk is flexible and belongs anywhere two different planes or materials meet, because those joints move. Grout in a tub-to-wall corner cracks out within a season. Caulk in a flat tile field traps moisture. Use each where it belongs.

Related: If stripping the old caulk revealed soft or damaged wall behind the tub, how to patch drywall covers cutting back to solid material and setting a proper patch before you seal anything. Budgeting the whole room? Start with the bathroom remodel cost guide, and if the tub is coming out entirely, shower installation cost has the separate numbers for that swap.