Why is grout discolouring in my Toronto shower already?

Grout discolouration in a shower that's only a few years old (or even months old) usually comes down to one of three culprits: moisture trapped beneath the surface, mould and mildew growth, or a sealing failure. The good news is that most cases are diagnosable and fixable without a full renovation.

The most common cause in Toronto homes is inadequate or missing grout sealer. Grout is naturally porous, and without proper sealing, it absorbs soap scum, hard water minerals, and body oils almost immediately. Toronto's municipal water supply has moderate hardness, which means calcium and magnesium deposits build up faster than many homeowners expect — you'll often see this as a white, chalky discolouration or yellowing along grout lines. If your installer didn't seal the grout within 48–72 hours of installation, or skipped it entirely (unfortunately common with rushed jobs), this is almost certainly your issue.

Mould and mildew are the second major culprit, showing up as grey, black, or pink staining. Toronto's humid summers and the naturally steamy shower environment create ideal conditions for mould growth, especially in grout that wasn't sealed or in showers with poor ventilation. If your bathroom exhaust fan isn't pulling air effectively — or if it's venting into the attic instead of outside (a code violation under the Ontario Building Code) — moisture lingers and mould follows. Run your hand along the grout lines: if they feel soft, crumbly, or slightly recessed, moisture has already compromised the grout itself.

Installation issues are worth considering if the discolouration appeared quickly after a new tile job. Grout that was mixed too wet, applied over uncured thinset, or installed in a shower that was used too soon can cure unevenly, leading to blotchy or inconsistent colouring. Efflorescence — a white powdery residue — happens when water moves through grout and deposits salts on the surface, often a sign of moisture coming from behind the tile.

For next steps, start with a simple water test: drop a few beads of water on the grout. If it absorbs within 30 seconds, the sealer is gone and resealing is your first move. Clean the grout thoroughly with a pH-neutral cleaner or a diluted hydrogen peroxide solution (avoid bleach long-term — it degrades grout), let it dry completely for 24–48 hours, then apply a penetrating silicone-based grout sealer. This is a legitimate DIY task that costs $20–$50 in materials.

If the grout is crumbling, deeply stained, or mould has penetrated below the surface, professional regrout or regrouting is the right call. In the GTA, expect to pay $300–$600 for a standard shower regrout, or $800–$1,500+ if the tiles need to be pulled and waterproofing inspected underneath. If your shower was recently installed and is already failing, that's a conversation to have with your original contractor — poor workmanship within 1–2 years may be covered under their warranty.

You can browse experienced tile and bathroom contractors in our directory at the Toronto Construction Network to get a few opinions before committing to any repair work.