A.Mark Knaebe responds: Treated lumber is not the source of your deck-painting difficulties. Clean, dry CCA-treated lumber is actually a better surface to paint than untreated wood of the same species. The real problem is that a paint’s performance suffers on a horizontal surface that is exposed to the weather. To make matters worse, deck boards are usually flat-grained, high-density wood that doesn’t hold paint as well as edge-grained, low-density wood.

For exterior decks, you’re better off using a water-repellent preservative or a penetrating-type semitransparent pigmented stain. Solid-color stains and film-forming paints aren’t recommended for horizontal surfaces because they may fail early. Hard enamel paints lack the flexibility to accommodate the movement of exposed wood. Flexible latex...

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