What is the best exterior paint for north-facing walls in NB that get mildew and algae growth?

For north-facing walls in New Brunswick that attract mildew and algae, you want a premium 100% acrylic latex exterior paint with built-in mildewcide, applied over a properly cleaned and treated surface. The paint choice matters, but the surface preparation matters even more — no paint will stay mildew-free if applied over an existing colony.

North-facing walls in NB get the worst of it: limited direct sunlight, slow drying after rain, persistent cool moisture, and often full shade for much of the day. Miramichi, Fredericton's older west-side neighbourhoods, and many homes in the Saint John River Valley see heavy algae growth on north exposures every two or three years because the conditions are essentially ideal for biological growth. The key is attacking this problem from both sides — prep and product.

Preparation is non-negotiable. Before any paint goes on, the surface must be thoroughly cleaned with a mildewcide wash. A solution of one part household bleach to three parts water, applied with a pump sprayer and scrubbed in, then rinsed after 15 minutes, kills existing mildew and algae effectively and cheaply. Commercial mildewcide products like Wet and Forget or a purpose-made exterior wash concentrate work even better. After washing, rinse thoroughly and let the surface dry for 48 to 72 hours minimum. Check wood moisture content with a moisture meter — you need below 15% before painting.

For the paint itself, look for these specific qualities: 100% acrylic latex (not vinyl-acrylic, not alkyd), built-in mildewcide, and high-quality titanium dioxide pigment for UV resistance even on shaded walls. Products that NB painting contractors consistently reach for on problem north exposures include Benjamin Moore Aura Exterior, Sherwin-Williams Duration, and Dulux WeatherShield. These are in the 5-80/gallon range but deliver noticeably better mildew resistance and durability than mid-grade alternatives.

Colour choice also plays a small role. Lighter colours show mildew more visibly but actually absorb less heat and reduce the thermal stress on the coating. Darker colours on north-facing walls can hide algae longer but may create more condensation-related issues in NB's humid climate. A mid-tone colour in a low-sheen satin finish (rather than flat, which holds moisture against the surface) is a practical choice for problem north walls.

One more step worth considering: after painting, an annual or biennial spray of a diluted mildewcide concentrate (like Wet and Forget Ready-To-Use) on north-facing walls in late spring acts as preventive maintenance that significantly extends the time before mildew can re-establish. This is a quick DIY task that takes 20 minutes per side of the house and is vastly easier than a full strip and repaint every three years. If the problem keeps returning despite quality paint and proper prep, investigate whether there's a moisture source nearby — a leaking gutter, a sprinkler system hitting the wall, or poor drainage at the foundation — that is keeping the wall perpetually damp.

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