Stand in any tiled shower and you are looking at two materials doing two very different jobs. Grout is the rigid, cement-based filler between tiles. Caulk is the flexible sealant where surfaces meet. Mix up which goes where and the joint fails: grout cracks along the tub edge, or caulk smeared between tiles peels and traps grime. The rule that decides it is simple, and once you know it you can read any bathroom from Vancouver to Halifax and spot what was done right.
The one rule: grout on the plane, caulk at the change
Grout belongs in field joints, the joints between tiles on the same flat surface. A wall of tile, a tiled floor, a niche back: everything within a single plane gets grout.
Caulk belongs at every change of plane and wherever tile meets a different material. In a typical bathroom that means:
- Inside corners where wall meets wall
- The joint where tiled walls meet the tub rim or shower base
- Where tile meets the ceiling or an adjacent painted wall
- Around tub spouts, valve trim and shower door frames, where the manufacturer calls for sealant
- Along the floor where tile meets a different flooring material
The reason is movement. Framing shrinks and swells with the seasons, and Canadian homes see real swings, from humid summers to bone-dry forced-air winters. An acrylic tub flexes every time it is filled. Two walls meeting at a corner move independently. Grout is rigid and cannot absorb any of that, so at a plane change it cracks, and cracked grout at a wet joint is an open door for water into the backer board and framing behind it. Caulk stretches and recovers, which is exactly what those joints need.
Silicone vs acrylic: an honest comparison
In the sealant aisle the choice comes down to two chemistries, each with a legitimate place.
| Factor | 100% silicone | Acrylic latex (siliconized) |
|---|---|---|
| Water resistance | Excellent, fully waterproof | Fair, degrades with constant soaking |
| Flexibility over time | Stays elastic for many years | Hardens and shrinks sooner |
| Ease of application | Unforgiving, needs careful tooling | Easy to tool, cleans up with water |
| Paintable | No | Yes |
| Best use | Tub and shower wet joints | Trim and gaps outside the splash zone |
For the joints that actually get wet, 100% silicone is the honest answer. It costs more per tube and is fussier to apply: you get one chance to tool a clean bead, and fresh silicone will not bond to old silicone residue, so surface prep matters. In exchange you get a joint that stays flexible and waterproof for years instead of seasons. Acrylic caulk earns its keep on baseboards, casings and the gap between a vanity backsplash and a painted wall, where paintability and easy cleanup matter more than immersion resistance. Hybrid formulas exist, but read the tube: if it is not rated for tubs and showers, it is not the one for the wet zone.
Colour matching without regret
A caulk line that clashes with the grout will bother you every day, so plan the colour before you cut the tube. Most major grout manufacturers sell caulk colour-matched to their grout palettes, including sanded-texture versions that mimic sanded grout, which makes the transition from grouted field joints to caulked corners nearly invisible. Two safe fallbacks: clear silicone, and crisp white against white fixtures. White caulk against a coloured grout, though, draws a bright outline around every corner and rarely looks intentional.
What mould-resistant claims really mean
Mould-resistant caulk contains a mildewcide additive that slows surface mould growth. It works, but it is a delay, not a force field, and the additive gradually leaches out over the life of the bead. No tube of caulk overcomes a bathroom that never dries. Ventilation is the real defence, and it matters most in a Canadian winter when the window stays shut for months: run the exhaust fan during every shower and for twenty to thirty minutes after, and rinse away soap film, because mould feeds on the residue sitting on the caulk more than on the caulk itself. If mould is growing under the surface of a bead rather than on it, cleaning will not fix it. Cut it out and recaulk.
When cracking caulk is a symptom, not a supply problem
Some cracking is routine. A hairline gap after years of service means the bead has aged out, and a one-time crack in a new build often just reflects settling. Recaulk and move on. One classic trick for the tub-to-tile joint: fill the tub with water before you caulk, let the bead cure, then drain. The tub sits at its lowest loaded position while the silicone sets, so the joint is not stretched every time someone takes a bath.
Persistent cracking is different. If a fresh bead splits again within weeks, if the gap visibly opens and closes with the seasons, or if the cracked caulk comes with cracked tiles, loose grout radiating across the wall, or a base you can feel flexing underfoot, the caulk is reporting a movement problem it cannot solve. That can mean an unsupported tub apron, a base installed without a proper mortar bed, or framing and deflection issues. Sealant is not structure. At that point it is worth having a contractor or plumber assess it, and if the verdict is that the fixture itself is at fault, our guides to standard bathtub sizes and shower base sizing will help you scope a replacement that fits the existing footprint.
A maintenance rhythm that works
- Weekly: rinse the walls after the last shower and run the fan. Cheap, boring, effective.
- Twice a year: inspect every caulked joint. Press gently along the bead and look for gaps, lifting edges or shadowy discolouration underneath.
- Every few years: plan to recaulk a busy shower. Remove the old bead completely, clean off every trace of silicone residue, let the joint dry fully, then run the new bead.
- Per the manufacturer's schedule: reseal cementitious grout so the field joints shed water instead of absorbing it.
Modern shower bases with integrated tiling flanges and properly sealed shower doors also shrink the number of vulnerable joints in the first place, worth remembering if a renovation is on the horizon. Everything ships across Canada, so the same logic applies whether the bathroom is in Victoria, Winnipeg or St. John's.
Frequently asked questions
Can I use caulk instead of grout between tiles?
No. Field joints between tiles on the same plane need grout. Caulk in those joints looks acceptable for a short while, then peels, stains and traps dirt, and it does nothing to lock the tile edges together the way cementitious grout does. Save caulk for corners, plane changes and fixture meetings.
How often should a shower be recaulked?
Let condition decide rather than the calendar. A quality silicone bead in a well-ventilated bathroom can last many years, while a busy shower that stays damp may need attention much sooner. Recaulk whenever you see cracking, lifting edges, or mould beneath the surface of the bead.
Should the caulk colour match the grout?
Usually, yes. Colour-matched caulk from the grout manufacturer, in a sanded texture if your grout is sanded, makes corners blend into the field tile. Clear silicone is the safe fallback, and bright white belongs on white-on-white installations where it reads as a clean line rather than an outline.
Why does my fresh caulk keep cracking in the same spot?
Repeated cracking in one spot usually means the joint is moving more than the sealant can stretch, or the new bead went over old silicone residue and never bonded. Strip back to clean, bare surfaces and use a tub-rated 100% silicone. If it still splits within weeks, treat it as a movement symptom and have a professional check the support under the tub or base.
