Metal flashing, gutters, and downspouts need specific primers and paints to stop corrosion during exterior house painting.

Start by removing loose rust and scale with a wire brush or coarse sandpaper until you reach clean metal; for heavy rust use a rust converter that chemically stabilizes remaining corrosion and follow with thorough drying. Choose a rust inhibitive primer suitable for the metal type, such as a zinc-rich primer for galvanized steel or an epoxy-based primer for heavily corroded areas, and apply thin, even coats to avoid drips and ensure adhesion. For topcoats use either oil-based paints formulated for metal or metal-specific acrylics that list corrosion protection on the label, applying two coats for uniform coverage and allowing full flash times between coats as the manufacturer specifies. When aiming for a glossy, long-lasting finish, lightly sand between primer and topcoat with fine grit to level imperfections and remove nibs, then wipe with a solvent-compatible tack cloth to remove dust. For seams and joints, use a paintable, exterior-grade sealant after priming edges and before final topcoating so the sealant bonds to primed metal and the paint ties into the joint. If the flashing is extensively pitted or the coating failures are recurring, consider replacing with coil-coated flashing where the factory-applied coating is baked on, which provides a far longer service life and reduces maintenance frequency.

Common mistakes include painting over rust without proper preparation which leads to rapid coating failure, so remove loose corrosion and treat or prime bare metal before topcoating. Another issue is using the wrong primer or topcoat; do not substitute general-purpose latex house paint for metal work, instead match primer and topcoat chemistry for compatibility. A third frequent problem is poor edge and seam treatment that allows water ingress and undercutting of the paint film; solve this by priming exposed edges, using a paintable exterior sealant at joints, and ensuring overlapping laps shed water away from exposed metal.

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