Why are my deck post bases rotting in Riverview NB?

Your deck post bases are rotting because the wood is in direct or near-direct contact with the ground without adequate drainage, and ground-level moisture is wicking into the end grain of the posts continuously. End grain absorbs water at 10 to 15 times the rate of face grain, so even pressure-treated lumber will deteriorate when the base sits in a persistently wet condition. In Riverview, where the Petitcodiac River valley's clay-heavy soils retain moisture and the water table can be high in low-lying areas, post base rot is one of the most common structural deck failures.

The fundamental problem is how water interacts with the post base. When a post sits directly on a concrete footing or pier without a standoff, rainwater, snowmelt, and ground moisture collect in the joint between the post bottom and the footing surface. That thin film of water never fully evaporates because the post blocks airflow and sunlight. In Riverview's climate, with over 1,100 mm of annual precipitation and snow cover persisting from December through March, that joint stays wet for months at a time. The pressure treatment chemicals in the lumber slow the decay process but do not stop it indefinitely, particularly at the end grain where the chemical penetration is shallowest.

Posts that were set directly into concrete or buried in the ground without a gravel drainage bed are the worst cases. The concrete wicks ground moisture directly into the wood, and once rot begins at the base it progresses upward through the post interior where you cannot see it. By the time the outside surface shows obvious decay, the post may have lost 40 to 60 percent of its structural cross-section internally. This hidden rot is dangerous because the post can appear sound from the outside while being critically weakened on the inside.

To repair rotted post bases, the standard approach is to cut the post above the rotted section and install a metal post base connector. Temporarily support the beam above the post using an adjustable jack post placed beside the affected post. Cut the decayed post cleanly at a point above all visible rot, typically removing the bottom 6 to 12 inches. Install a galvanized or stainless steel post base bracket onto the concrete footing using concrete anchor bolts. The metal bracket elevates the bottom of the post approximately 1 inch above the footing surface, creating an air gap that allows water to drain and the end grain to dry. Set the freshly cut post into the bracket, check for plumb, and secure with the bracket's through-bolts or structural screws.

If the concrete footing itself is in poor condition, crumbling or undersized, this is the opportunity to replace it entirely. Dig down to below the 4-foot frost line, pour a new footing that is at least 18 inches in diameter with a flat top surface, set the metal post base bracket into the wet concrete with the anchor bolt template, and let it cure for at least 48 hours before loading.

For prevention going forward, every post on your deck should have a metal standoff base that keeps the wood above the footing surface. Brush-apply additional end-cut preservative to any freshly cut post bottoms before setting them in the bracket. Ensure the grade around each footing slopes away so surface water drains clear rather than pooling at the post base. In Riverview's clay soils, adding a ring of 3/4-inch crushed stone around each footing improves drainage significantly and reduces the moisture load that caused the rot in the first place.

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