How do you fix stucco discolouration and efflorescence on an Ottawa home?

Those white, chalky streaks or patches on your stucco are efflorescence—mineral salts that get carried to the surface by moisture moving through the wall. It's one of the most common cosmetic issues on Ottawa stucco homes, especially visible on darker-coloured finishes. While efflorescence itself isn't structurally harmful, it's a clear signal that moisture is moving through your stucco, which in Ottawa's freeze-thaw climate is something worth addressing.

Understanding the Problem

Efflorescence happens when water dissolves soluble salts (primarily calcium carbonate) from the cement in stucco, concrete, or mortar. As water migrates to the surface and evaporates, those salts crystallize as a white deposit. In Ottawa, you'll notice it most in spring after snowmelt, and on north-facing walls that stay damp longer.

Discolouration beyond efflorescence can also come from:

• Algae and mildew growth — especially on shaded, north-facing walls where Ottawa's humid summers create ideal growing conditions- Rust staining — from corroding metal lath, fasteners, or flashing behind the stucco- Dirt and pollution buildup — particularly near busy roads or construction sites- Uneven weathering — areas sheltered by overhangs age differently than exposed sections

How to remove efflorescence:

• Dry brushing — Start with a stiff natural-bristle brush on dry stucco. Many light efflorescence deposits come off with dry brushing alone. Don't use a wire brush—it damages the stucco surface.- Water and vinegar solution — For moderate deposits, a 50/50 white vinegar and water solution applied with a brush, left for 5–10 minutes, then rinsed with clean water works well.- Muriatic acid (diluted) — For heavy, persistent efflorescence, a 10:1 water-to-muriatic-acid solution is effective. Wet the wall first, apply the solution, scrub, and rinse thoroughly. Wear proper protective equipment and protect landscaping below.- Commercial efflorescence removers — Products like Prosoco Sure Klean or Dumond are formulated specifically for masonry and stucco. They run $25–$50 per container.

For algae and mildew: A solution of 1 part bleach to 3 parts water, applied and left for 15 minutes before rinsing, handles most biological growth. Follow up with a mildew-resistant paint or sealer.

Preventing recurrence is the real fix. This means:

• Applying a breathable silane/siloxane water repellent ($150–$400 for a typical Ottawa home)- Fixing any grading issues that direct water toward the foundation- Ensuring downspouts discharge well away from stucco walls- Checking and resealing caulk joints at windows and penetrations annually

Professional stucco cleaning and sealing in Ottawa runs $500–$1,500 depending on the home's size. If efflorescence keeps returning despite cleaning, you may have a moisture issue behind the wall that needs investigation—budget $300–$600 for a professional assessment.

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

• 613Bins
• RenoMotion Inc.
• Capital City Drywall
• Denys Builds Designs Renovations
• Somar Contracting Inc.

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