How do I prepare cedar shingle siding for painting on a New Brunswick home?

Preparing cedar shingle siding properly is about 70% of the battle — a rushed prep job on cedar will result in peeling paint within two to three NB winters, regardless of what you spend on paint. Cedar is porous, resinous, and highly sensitive to moisture, so each preparation step matters.

Cedar shingle siding is found on a huge proportion of older New Brunswick homes, particularly in Saint John, Fredericton, and rural communities. Many of these homes have had multiple paint layers applied over decades, and the first step is assessing the condition of existing paint. If the paint is alligatoring (a pattern of cracks resembling alligator skin), bubbling significantly, or peeling in large sheets, it needs to be fully stripped — not just scraped around the edges. Old paint layers on cedar will delaminate and bring new paint down with them.

Once any loose or failing paint is removed, work through these preparation steps:

Clean the surface thoroughly. Cedar shingles in NB’s damp climate attract mildew, algae, and surface dirt. Pressure wash at moderate pressure (1,000–1,500 PSI on a fan tip — not a narrow jet that will blast the soft summer wood out of the grain) using a solution of 1 part bleach to 4 parts water with a squirt of dish soap. This kills mildew spores. Allow the shingles to dry completely — a minimum of 48-72 hours of dry weather in June or July, longer in September’s cooler air.

Test moisture content. Before priming, check that shingle moisture content is below 15% using an inexpensive pin-type moisture meter. In NB’s wet springs, cedar shingles commonly read 20-25% or higher into May — painting over wet cedar is the primary reason exterior paint fails prematurely on NB homes.

Address knots and resinous areas. Cedar has natural oils and resin pockets that bleed through paint, causing brown staining. Spot-prime these areas with a shellac-based primer like Zinsser BIN before applying your full coat of primer. On new or bare cedar, a penetrating alkyd primer is preferable to a waterborne primer — it soaks into the open grain and bonds more effectively than a latex primer on raw cedar.

Caulk gaps selectively. Caulk the top edge of each shingle course where it meets the course above, and around window and door trim. Do NOT caulk the butt edges (the exposed bottom edges) — cedar needs to drain and breathe through the butt edges, and sealing them traps moisture inside the wall.

For the finish coat, use a premium 100% acrylic latex exterior paint in a satin finish. Two full coats are the minimum — and on cedar that has been stripped or has significant bare wood, you may find you need three coats to get solid, even coverage. For professional-quality results on a full cedar exterior, this is genuinely a job that benefits from an experienced contractor who knows NB’s cedar housing stock.

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