What is the best way to prepare rough-sawn T1-11 or board-and-batten plywood siding for painting on a New Brunswick garage or outbuilding?

Rough-sawn T1-11 and board-and-batten plywood siding requires aggressive surface preparation to achieve a durable paint finish that will survive New Brunswick's harsh freeze-thaw cycles and Maritime humidity. The deep grooves and rough texture trap moisture and dirt, making proper cleaning, priming, and paint selection critical for longevity.

Surface Cleaning and Repair

Start by power washing the siding with a 2500-3000 PSI pressure washer, working from top to bottom. The rough texture of T1-11 collects years of dirt, pollen, and mildew that must be completely removed. Use a fan tip and keep the nozzle 12-18 inches from the surface to avoid gouging the wood fibers. For stubborn mildew (common on north-facing garage walls in NB's humid climate), add a mildew cleaner or diluted bleach solution before pressure washing. Allow the siding to dry completely for at least 48-72 hours after washing — moisture trapped in the deep grooves takes longer to evaporate than smooth siding.

Inspect every panel for loose or raised edges, particularly around the bottom where moisture damage is most common. T1-11 is notorious for delaminating at the edges when exposed to repeated wet-dry cycles. Secure any loose areas with galvanized screws and fill gaps with exterior wood filler. Sand down any splintered or fuzzy areas with 80-grit sandpaper, but don't over-sand — the rough texture actually helps paint adhesion.

Critical Priming Step

Never skip primer on T1-11 siding — this is the most common mistake that leads to paint failure within 2-3 years. The factory-applied primer on new T1-11 is minimal and degrades quickly under UV exposure. Use a high-quality oil-based or acrylic primer specifically designed for rough wood surfaces. Sherwin-Williams ProBlock or Benjamin Moore Fresh Start are excellent choices that penetrate deeply into the wood grain and seal the surface properly.

Apply primer with a thick-nap roller (15-20mm/5/8 to 3/4 inch) to work the primer into all the grooves and texture. Back-brush immediately with a 4-inch brush to ensure complete coverage in the deep channels. The rough surface will consume more primer than smooth siding — budget for 25-30% more material than the coverage rate on the can suggests.

Paint Selection for NB Climate

Choose a 100% acrylic latex exterior paint in satin or semi-gloss sheen. The slight sheen helps moisture run off rather than soaking into the wood grain, which is crucial for T1-11's longevity in New Brunswick's wet springs and humid summers. Flat paint on rough siding holds moisture and promotes mildew growth.

Premium options like Benjamin Moore Aura Exterior or Sherwin-Williams Duration Exterior provide the flexibility needed to handle freeze-thaw cycles without cracking. These paints cost $60-75 per gallon but will last 8-10 years on properly prepped T1-11, compared to 4-5 years for mid-grade paint.

Application Technique

Apply paint the same way as primer — thick-nap roller followed by back-brushing. Work in manageable sections (one full panel at a time) and maintain a wet edge to avoid lap marks. The rough texture requires two full coats for complete coverage and protection. Don't thin the paint — T1-11's deep grooves need full-strength paint to bridge the texture properly.

Timing for NB Conditions

Plan this project for late May through September when you can guarantee 3-4 consecutive dry days. T1-11's rough surface takes longer to dry than smooth siding, and morning dew can reactivate fresh paint if humidity is too high. Avoid painting in direct afternoon sun, which causes the paint to dry too quickly and prevents proper leveling.

When to Hire a Professional

Consider hiring a professional if your garage is two stories or if the T1-11 is severely weathered with extensive edge delamination. Professional painters have spray equipment that can achieve more even coverage in the deep grooves, and they carry the insurance needed for working at height. For a single-story garage or shed, this is a manageable DIY project that will save $1,500-3,000 in labor costs while giving you complete control over the prep quality.

Need help finding a painting professional for your T1-11 project? New Brunswick Painting can match you with experienced contractors who understand the specific challenges of rough-sawn siding in our Maritime climate.