How to Cut Out and Replace Caulk at a Tub or Counter

Why this matters

A caulk joint looks like the smallest part of a repair, and it is the part the customer touches every day. Run a new bead over old caulk, or over a joint that is still damp, and it peels within weeks, lets shower water behind the tile or into the cabinet, and grows a black line the customer blames on whoever touched it last. That is you. A clean recaulk takes longer than a cosmetic one mostly in waiting time, and the waiting is what makes it hold.

This card covers replacing a bead that your work disturbed or exposed, at a tub, shower, sink rim or countertop backsplash. Which sealant goes in which joint has its own card (see related: Sealant + Caulk Selection Quick Reference).

Before you start: blades, solvents and cleaners

• Blades. Utility knives and razor scrapers slip on glazed surfaces. Cut away from your other hand, use a fresh blade (a dull one needs force, and force is what slips), and use plastic blades on acrylic, fiberglass and cultured marble, which steel scratches.
• Solvents. Mineral spirits, isopropyl alcohol and caulk-remover gels are flammable and give off vapor in a small bathroom. Run the exhaust fan or open a window, keep ignition sources out of the room, and wear gloves the product's safety data sheet names.
• Mildew cleaners. Never mix a bleach cleaner with an ammonia or acid cleaner, or follow one with the other without rinsing; the mix releases toxic gas. Use one product, ventilate, wear eye protection and gloves, and rinse before using anything else.
• Old caulk in commercial buildings. Caulk in buildings built or renovated between roughly 1950 and 1979, mostly schools and commercial buildings, can contain PCBs, and EPA treats removing it as something to plan for, not improvise. In that setting, ask the facility whether the caulk has been tested before cutting it out.

Step 1: Cut both edges and pull the old bead

Score the old bead along both edges, where it meets each surface, with a utility knife or a caulk removal tool, then pull it out in as long a strip as it will give. Cutting both edges first lets it release from the joint instead of tearing and leaving a film on each face.

What breaks if you skip it: new sealant laid over old caulk bonds only to the old caulk, which is already failing, so the new bead fails along the old one's line. Latex caulk laid over silicone barely bonds at all.

Step 2: Remove every trace of residue

Scrape the remaining film off both faces with a plastic scraper. Silicone leaves a nearly invisible slick film; wipe the joint with isopropyl alcohol or the solvent the new sealant's data sheet recommends, and use a remover gel for stubborn residue, following its dwell time. Test any solvent on a hidden spot of an acrylic or cultured-marble surface first, because some solvents haze or craze those materials. Latex and acrylic residue softens with water and comes off with a scraper.

The test that you are done: drag a clean fingertip across the cleaned face. Silicone film feels slick; clean tile, enamel or laminate feels slightly grippy.

Step 3: Deal with the mildew and look at what is behind it

Black staining under old caulk is mold growth on the residue, the grout edge, or the surface behind. Clean surface staining with a mildew cleaner or a diluted bleach solution mixed as its label directs, rinse with plain water and let it dry.

Then look at the joint itself. Press the grout and the tile edge beside the joint. If the wall flexes, the grout is soft, or a screwdriver tip pushes into the backer behind the tile, the joint has been leaking long enough to damage the wall, and a new bead will only hide that. Stop, show the customer, and treat it as a water-damage repair, not a caulk job (see related: Plan the Restore Before You Remove the Finish).

Step 4: Let the joint dry completely

Sealant does not bond to a wet surface, and water sealed into the joint feeds mildew from behind the new bead. A tub joint that has been wet for years, or was just rinsed, needs at least overnight with the exhaust fan running and the shower unused, longer if the grout beside it still looks darker than the grout higher up. Tell the customer before you start that this is a two-visit job, or a return-the-next-morning job, and why.

Rushing it is the most common reason a professional recaulk peels.

Step 5: Load the tub, then size and back the joint

For a tub-to-wall joint, fill the tub with water before caulking. The weight settles the tub to the position it sits in when someone is standing in it, which opens the joint to its working width. Caulked empty, the joint is stretched every time the tub is used, and the bead tears at its edges. Leave the water in until the sealant reaches the cure the tube states.

Measure the gap. Typical practice for a wide or deep joint is to press closed-cell backer rod (a foam cord) into the gap so the sealant bead is about half as deep as it is wide and bonds only to the two faces, not the bottom; confirm the widths and depth ratio on the sealant's data sheet. A bead bonded on three sides cannot stretch and splits down the middle.

Step 6: Tape both sides of a wide or visible joint

For a joint wider than a pencil line or anywhere the bead's edge will be seen up close, run painter's tape along both faces, leaving the exact bead width open. Tape turns a wavy freehand edge into two straight lines, and it catches smears that would otherwise need solvent on a fresh bead.

Step 7: Choose the sealant for the joint, and apply it in one go

Wet joints at tubs, showers and sinks get a sealant rated for that exposure, usually a mildew-resistant silicone; a dry, paintable joint at a counter edge or trim may get a siliconized acrylic. Natural stone needs a sealant labeled for stone, because some sealants stain it. The quick-reference card covers the choices.

Cut the nozzle at an angle to the bead width, hold the gun at a steady angle and push the bead ahead of the nozzle in one continuous run per side, rather than stopping and restarting, which leaves lumps.

Step 8: Tool once, pull the tape wet

Tool the bead with one smooth pass of a tooling tool or a gloved finger, pressing lightly so the sealant wets both faces and forms a slight concave surface. Each extra pass drags skinned sealant and leaves ridges. Use a tooling aid only if the sealant's data sheet allows it; some aids interfere with adhesion.

Pull the tape immediately, while the bead is wet, peeling it back on itself away from the joint. Tape left until the bead skins tears the edge.

Step 9: Give the customer the cure time

Read the tube for two figures, not one: the time until the surface is tack-free, and the time until the joint may be wet. They are often very different. Write the second one on the ticket and tell the customer in words, with the clock time it ends.

Worked example: a tub perimeter after a leak repair

A plumber is called for a stain on the kitchen ceiling under a bathroom. From the access panel the plumber finds and replaces a failed overflow gasket. A flood test of the tub with the shower running also shows water getting behind the tile at the end wall, where the old silicone bead has pulled away from the tub. The plan, agreed before work, is to cut out and replace the whole tub-to-tile bead, back wall and both end walls.

The joint. A 60 in tub against three walls: 60 in at the back and 30 in at each end, so 120 in, or 10 ft, of joint. The gap is about 1/8 in along the back wall and opens to about 3/8 in at the leaking end.

Cut and clean. Both edges scored with a plastic-blade scraper, since the tub is acrylic. The old silicone pulls out in four strips. Residue scraped, then wiped with isopropyl alcohol after a test on the tub's apron showed no hazing. Black staining on the grout edge at the leaking end cleans off with a diluted bleach solution, rinsed. Pressed by hand, the tile and grout at that end are firm, and a screwdriver tip does not push into the backer, so this stays a caulk job.

Dry. The grout at the leaking end is visibly darker than the grout a foot up the wall. The plumber runs the fan and comes back the next morning, when the grout reads the same color all the way up.

Load, back and tape. Tub filled with water. Backer rod pressed into the 3/8 in section at the end wall; the 1/8 in gap along the back needs none. Tape on tile and tub, leaving about 1/4 in open along the back and a little more than the 3/8 in gap at the leaking end.

How much sealant. Estimated at a 1/4 by 1/4 in bead, the cross-section is 0.25 x 0.25 = 0.0625 sq in. Over 120 in, that is 120 x 0.0625 = 7.5 cu in. A 10.1 fl oz cartridge holds about 18.2 cu in (10.1 x 1.805), so the job uses about 41 percent of one cartridge before waste, a little more for the wider end section. One tube of mildew-resistant silicone, plus a spare for safety.

Apply and tool. One run per wall, one tooling pass, tape pulled wet.

Cure. The tube states the bead is tack-free in under an hour and ready for water after 24 hours. The ticket says: "Tub left full; do not drain or shower before 9:30 tomorrow morning."

What would change the call. A soft wall at the leaking end makes it a wall repair before any caulk. A natural-stone tub deck would need a stone-rated sealant. In an older school's restroom, the old caulk gets tested for PCBs before the knife comes out.

How to verify

Before you leave: the bead is continuous with no pinholes or gaps at the corners, the tape lines are straight, both faces are wetted along the whole run, and no smears are left on the tile or tub. After the cure time, and not before, run the shower against the joint and check the edge and, where reachable, the area below or behind for water. On a leak repair, ask the customer to check the ceiling stain is dry after the first few showers, and note that follow-up on the ticket.

References

• EPA guidance on PCBs in building caulk, for buildings built or renovated about 1950 to 1979.
• Sealant manufacturer product data sheets: joint dimensions, backer rod, tooling aids, cure times.
• Safety data sheets for the solvents and cleaners used.
• See related: Sealant + Caulk Selection Quick Reference; Plan the Restore Before You Remove the Finish.