What type of grout is best for preventing mold growth in an Ottawa bathroom shower?

Epoxy grout is the best choice for preventing mould growth in an Ottawa bathroom shower, and it is not even close. Unlike cementitious grout, epoxy grout is completely non-porous — water, soap residue, and mould spores simply cannot penetrate its surface. It never needs sealing, it resists staining, and it maintains its colour and integrity for decades even in the wettest shower environments.

The reason mould thrives in shower grout comes down to porosity. Standard cementitious grout — both sanded and unsanded varieties — is inherently porous. Even when sealed, those tiny pores absorb moisture over time, and that trapped moisture creates the perfect breeding ground for mould and mildew. In Ottawa, this problem is amplified by the dramatic humidity swings between seasons. During the humid summer months, bathroom humidity can stay elevated for extended periods, feeding mould colonies that established themselves in damp grout. Then during winter, when indoor air is bone-dry from forced-air heating, the grout dries out and cracks, creating even more pathways for moisture infiltration once humidity returns.

Epoxy grout does cost more — roughly $2 to $4 per square foot for materials compared to $0.50 to $1.50 for cementitious grout — and it is more difficult to work with, requiring faster application and more careful cleanup during installation. Most professional tile installers charge a modest premium for working with epoxy, typically adding $1 to $3 per square foot to labour costs. But when you factor in the money and effort you will save by never needing to seal the grout, never scrubbing mould, and never regrouting due to deterioration, epoxy pays for itself within a few years.

If epoxy grout is not in the budget, the next best option is a high-quality sanded cementitious grout with built-in antimicrobial additives, sealed with a penetrating grout sealer immediately after curing and re-sealed every 12 to 18 months. Products with silver-ion antimicrobial technology do slow mould growth, but they do not eliminate it the way epoxy's non-porous surface does. Proper bathroom ventilation is also critical — run your exhaust fan for at least 20 minutes after every shower and ensure it vents to the exterior, not into the attic. In Ottawa's climate, attic-vented bathroom fans create ice damming and moisture problems in the roof space during winter.

For a shower regrouting project or a new shower tile installation where mould prevention is a priority, a professional installer experienced with epoxy grout will deliver the best results.

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Looking for experienced contractors? The Ottawa Construction Network connects Ottawa homeowners with qualified professionals:

• Homeupgraders
• JC Carpentry
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• Engur Construction
• COCO TILE