Caulking a tub looks like a five minute job, and the actual bead application genuinely is. The reason so much bathtub caulk fails within a year has almost nothing to do with the caulk itself and almost everything to do with what was, or was not, done before it went on, starting with what is already there.
Removing the old caulk completely
A new bead run directly over old caulk will not bond to either surface, so it has to come off fully first.
- Cut along both edges of the old caulk bead with a caulk removal tool or a sharp utility knife.
- Pull the loosened bead away in strips, working slowly rather than tearing it in one motion.
- Scrape any remaining residue off the tub and tile with a plastic scraper to avoid marking either surface.
- Wipe the joint with a cloth and check for any remaining film. A new bead run over old residue, even a thin one, will not bond properly to either surface.
Cleaning and drying the joint
What happens between removal and the new bead matters as much as either step on its own.
- Wipe the whole joint with isopropyl alcohol to remove soap residue, body oils and any mould that has taken hold in the grout line.
- Pay particular attention to the corners, where mould and residue both tend to concentrate.
- Let the joint air dry completely, ideally overnight rather than a couple of hours.
- Confirm it is fully dry before moving on. Caulk applied over a damp joint seals the moisture in rather than keeping it out, which is the opposite of what caulk is meant to do.
Filling the tub with water first
This is the step almost everyone skips, and it matters more than most of the others combined. Fill the tub with water before caulking, enough to weigh it down and drop it to roughly the position it sits in during actual use. Caulk applied to an empty, unweighted tub sets in that raised position, and the first time someone takes a bath, the tub drops slightly under the extra weight and the caulk bead cracks along the bottom edge almost immediately, often within the first week. Draining the tub only after the caulk has fully cured avoids this entirely.
Applying the bead
With the prep done properly, the actual application is the fast, satisfying part.
- Cut the tip of the caulk tube at a low angle for a thin, controllable bead rather than a wide opening.
- Load the tube into a caulking gun and run the bead in one continuous motion along the joint, rather than starting and stopping.
- Smooth the bead immediately with a wet finger or a purpose-made caulk smoothing tool, in a single pass.
- Tool the excess off onto a rag rather than reworking the same section repeatedly, which tends to pull caulk back out of the joint.
- Let it cure fully, usually about 24 hours, before draining the tub or using the shower.
If the tile or tub surround itself needs attention as well, our caulking and drywall service in Kitchener, Waterloo and Cambridge can handle the surround and the seal in the same visit.