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The line of caulk where the tub or shower base meets the tile does more than look tidy. It stops water running down behind the wall and into the floor, which is how a great many ceiling stains in the room below begin. Caulk lasts a few years, then cracks, pulls away or grows black mold. Replacing it is not difficult, but it has to be done thoroughly.
When it needs doing
- Gaps or cracks along the joint
- Mold that comes back no matter how it is cleaned
- Caulk that has pulled away from the tub or the tile
- A stain on the ceiling below the bathroom, after other causes have been ruled out
Tools and materials
- A caulk removal tool or a plastic razor scraper, and a utility knife
- Rubbing alcohol, or a mildew cleaner, and a cloth
- A tube of 100% silicone caulk for kitchens and baths, with mildew resistance. White or clear, or a color to match the tub.
- A caulk gun, painter's tape, paper towels, and a bowl of soapy water
Avoid ordinary acrylic latex caulk in a wet area. It fails quickly.
Step by step
- Remove all the old caulk. This is most of the job and it cannot be skipped: new silicone does not stick to old silicone. Cut along both edges with the knife, then pull and scrape out the bead. A caulk remover softener helps on stubborn silicone. Go over the joint again with the scraper until it is clean tile and tub.
- Clean and kill the mold. Wipe the joint with a mildew cleaner, rinse, then wipe with rubbing alcohol to remove soap film. Let it dry completely, ideally overnight with the bathroom fan on.
- Fill the tub with water. A tub flexes and sinks slightly under the weight of a bather. Caulking it full means the joint is at its widest, and the caulk will be compressed, not stretched, in use.
- Tape both sides of the joint, leaving a gap about a quarter inch wide. This gives a straight edge and saves clean-up.
- Cut the tube tip at a 45-degree angle, with a small opening. Run a steady bead along the joint, pushing the gun rather than pulling.
- Smooth it with a finger dipped in soapy water, or a caulk finishing tool, in one long pass. Wipe your finger often.
- Pull the tape immediately, at an angle away from the joint, before the caulk skins over.
- Leave it for the time on the tube, usually 24 hours, before running water. Drain the tub only after the caulk has cured.
The corners and the floor
Do the vertical corners of the tile in the same way if they are caulked rather than grouted. Do the joint where the tub meets the floor too; it is the one that lets water under the flooring.
Grout is different
If the cracks are in the grout lines between tiles rather than the caulk joint, that is a grout repair, and the joint between different materials, tub to tile, should always be caulk, not grout, because it moves.
When to call a plumber
Caulk is not a plumbing job, but what caulk was hiding sometimes is. If the tile behind the joint is loose, the wall is soft, or water is still reaching the ceiling below after the caulk is replaced, the cause is likely the shower drain, the tub overflow gasket, or the valve in the wall. For those, find a licensed plumber near your town.