What causes the grout in my shower to crack every year, and how do I fix it permanently?

Recurring grout cracking in a shower is almost always caused by movement — either the substrate is flexing, the wrong type of grout was used, or grout was applied where caulk should have been. This is one of the most common bathroom complaints among GTA homeowners, and the good news is that the underlying cause can usually be identified and corrected.

The most frequent culprit is using grout in change-of-plane joints — where the shower floor meets the wall, where two walls meet in a corner, or where tile meets the tub rim. These joints experience constant micro-movement from thermal expansion, building settling, and the daily wet-dry cycle of a shower. Grout is rigid and cannot accommodate movement, so it cracks repeatedly no matter how many times you regrout. The permanent fix is simple: remove the grout from all change-of-plane joints and replace it with 100% silicone caulk in a colour matched to your grout. Silicone is flexible and moves with the joint instead of cracking. This is a repair you can do yourself for under $20 in materials.

Substrate Problems

If grout is cracking within the tile field (not just at corners and transitions), the problem is likely substrate deflection. This means the surface behind or beneath the tile is flexing under load or moisture. Common causes in Toronto homes include drywall used as tile backer instead of cement board (disturbingly common in older renovations and builder-grade finishes), a subfloor that is too thin or has damaged sections, or missing or inadequate thinset coverage behind the tile — if the tile is only adhered at the edges with hollow spots behind it, any pressure on the tile causes it to flex and crack the surrounding grout.

To test for hollow spots, tap the tiles with your knuckle. A solid, dull sound indicates full thinset adhesion. A hollow, ringing sound means the tile is not fully bonded to the substrate. Widespread hollow tiles combined with cracking grout usually means the tile installation needs to be redone properly — unfortunately, there's no patch fix for poor adhesion.

Wrong Grout Type

Unsanded grout in joints wider than 1/8 inch will crack because it lacks the structural strength for wider joints. Sanded grout should be used for joints 1/8 inch to 1/2 inch wide. For the best crack resistance, epoxy grout is the premium option — it's virtually impervious to water, doesn't need sealing, and resists cracking far better than cement-based grout. Epoxy grout costs more ($8–$15 per kg versus $3–$6 for cement-based grout) and is harder to work with, but it's an excellent long-term solution for showers. Many GTA tile installers now offer epoxy grout as a standard upgrade for shower installations.

The Permanent Fix

If your substrate is sound (cement board, no hollow tiles, solid subfloor) and the cracking is limited to corners and transitions, the fix is straightforward: remove cracked grout from all change-of-plane joints using a grout saw or oscillating tool, clean the joints thoroughly, let them dry completely, and apply 100% silicone caulk (not latex caulk, which degrades quickly in wet environments). Allow 24 hours of cure time before using the shower.

If the cracking is widespread across the tile field, you're likely looking at a larger project. A professional assessment will determine whether the tile can be re-grouted with a better product or whether the installation needs to be redone with proper substrate preparation and full thinset coverage. In the GTA, a professional regrout of a standard shower runs $400–$800, while a complete shower retile ranges from $5,000–$12,000 depending on size and materials.

Need help finding a professional bathroom renovator? Toronto Bath Remodeling can match you for free.