Why the Wrong Nails Ruin a Fence Before the Wood Ever Rots
Black, bleeding streaks running down a fence board are a fastener problem, not a wood problem — and the cause depends on what the fence is made of.
If the lumber is pressure-treated with ACQ (the modern standard), using regular galvanized nails is a mistake that compounds over time: those nails can corrode to failure within about three years, because ACQ’s chemical formulation is more corrosive to standard galvanized steel than older treatments were. There’s no cosmetic fix once the staining has set in on ACQ lumber — the only real solution is waiting until the fasteners fail and rebuilding with fasteners actually rated for ACQ contact (double-galvanized or better).
If the lumber is red or white cedar, the staining comes from a different chemical reaction — iron in the fastener reacting with tannins naturally present in the wood, and there’s no reliable way to remove those streaks once they’ve formed. For cedar, the practical fix is cosmetic rather than corrective: a solid stain or a very dark semi-transparent finish that hides the discoloration going forward.
Either way, the lesson is the same: match your fasteners to your lumber treatment before you build, because there’s no clean fix after the fact.