What are the differences between painting fibre cement siding like HardiePlank versus wood clapboard on a New Brunswick home?

Fibre cement and wood clapboard are fundamentally different substrates that require different prep approaches, primers, and paint systems — and in New Brunswick's climate, getting those differences wrong is expensive.

Both materials are common on NB homes, but they fail for opposite reasons: wood clapboard fails because it absorbs too much moisture, while fibre cement fails primarily because of inadequate surface prep and the wrong primer at installation or repainting time.

Wood Clapboard: Managing Moisture Is Everything

Traditional wood clapboard — whether it's spruce, pine, or cedar — is the dominant siding on older NB homes, and its biggest enemy is moisture. Before you touch a brush, check the wood's moisture content with a moisture meter. It must be below 15%. In NB, this rules out painting in April and early May almost entirely, when snowmelt and spring rain keep wood saturated for weeks. Even in summer, north-facing clapboard in shaded areas can hold moisture well above safe painting levels after a few rainy days.

Surface prep on wood clapboard means scraping all loose and peeling paint, sanding edges smooth, filling nail holes and cracks with exterior wood filler, caulking gaps at trim and corner boards, and priming every bare wood spot with an oil-based or shellac-based primer before topcoating. The end grain of clapboard — the bottom edge — is the most vulnerable spot on the whole board. Paint it carefully, because unpainted end grain wicks moisture like a straw and causes the boards to cup and split over time.

For the topcoat, 100% acrylic latex exterior paint is the right choice for wood clapboard in NB. It's flexible enough to expand and contract with the wood through freeze-thaw cycles without cracking, and it's breathable enough to let trapped moisture escape rather than building pressure behind the paint film. Oil-based paints were the standard for decades on NB clapboard homes, but they become brittle over time and crack badly under the 100+ freeze-thaw cycles NB sees annually. If you're repainting an older home that still has oil-based paint on it, you can apply acrylic latex over it — but the existing oil paint must be sound, clean, and lightly sanded for adhesion.

Mildew is a constant threat on wood clapboard, especially on north-facing walls and under soffits in communities like Shediac, Saint John, and the Fundy shore where humidity is persistently high. Never paint over mildew. Clean it with a bleach-and-water solution (1 part bleach, 3 parts water), let it dry completely, then prime and paint. Painting over mildew traps it under the new film and it grows right through within a season.

Expect a quality exterior paint job on wood clapboard to last 7-12 years in NB with proper prep, though south- and west-facing walls exposed to UV and prevailing Maritime winds may need attention sooner.

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Fibre Cement (HardiePlank): Primer Is Non-Negotiable

HardiePlank and other fibre cement sidings have become very popular on new NB construction and renovation projects over the past 20 years, and for good reason — they don't rot, they're dimensionally stable, and they don't feed carpenter ants or woodpeckers. But they are not maintenance-free, and they have their own specific painting requirements that catch a lot of homeowners off guard.

The most critical rule with fibre cement: it must be primed before painting, and the primer must be specifically formulated for fibre cement or masonry. Fibre cement is highly alkaline and porous. Apply a standard latex primer without the right chemistry and you'll get adhesion failure within a couple of years. James Hardie actually requires that their product be primed within a specific timeframe after installation — unprimed fibre cement left exposed to NB weather for more than a few months can absorb enough moisture to cause paint failure right from the start. If you're repainting HardiePlank that was factory-primed and painted at installation, check the existing paint condition carefully. If it's chalking, fading, or peeling, clean it thoroughly with a pressure washer (low pressure — fibre cement can be damaged by high-pressure washing), let it dry fully, spot-prime any bare areas, and then topcoat.

Moisture content matters less with fibre cement than with wood — the material doesn't swell and shrink the way wood does, so freeze-thaw movement is much less of a concern. This makes fibre cement somewhat more forgiving in NB's climate, but it doesn't mean you can skip drying time after rain. Paint applied to wet fibre cement still won't adhere properly.

For the topcoat, 100% acrylic latex exterior paint is again the right product — the same premium paint you'd use on wood clapboard works well on fibre cement. Two full coats are mandatory. Fibre cement is thirsty and the first coat soaks in more than you'd expect, especially on bare or newly primed surfaces. Skimping to one coat on fibre cement is a very common mistake that leads to uneven colour, poor durability, and early fading.

Cut edges are the vulnerability on fibre cement, just as end grain is the vulnerability on wood clapboard. Any time HardiePlank is cut during installation or repair, those cut edges must be sealed with a quality primer immediately. Unsealed cut edges absorb water, and in NB's freeze-thaw climate, that moisture causes the cement board to delaminate from the inside out. If you're repainting a home where the cut edges were never properly sealed, address them before topcoating.

Fibre cement holds paint longer than wood when properly primed — expect 10-15 years from a quality paint job on HardiePlank in NB conditions, versus 7-12 on wood clapboard.

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Side-by-Side Summary

Wood clapboard demands moisture management above all else — test moisture content, respect the spring painting window, prime bare wood aggressively, and use flexible 100% acrylic latex. Watch end grain, mildew, and caulking at joints.

Fibre cement demands the right primer chemistry — use a primer rated for fibre cement or masonry, seal every cut edge, pressure-wash gently before repainting, and plan on two full topcoats. Less movement than wood, but primer failure is the dominant cause of early paint breakdown.

In both cases, the exterior painting window in NB runs from mid-May through mid-October. Both substrates need surface temperatures above 10°C and ideally below 30°C, with no rain forecast for 24-48 hours after application.

If your home has two storeys, significant peeling, or you're unsure about the condition of the existing paint system, this is a project worth getting a professional assessment on. New Brunswick Painting can match you with a local painting professional for a free estimate — find contractors in your area through the New Brunswick Construction Network directory at newbrunswickconstructionnetwork.com/directory?trade=painting.