How to Prepare Exterior Surfaces for Painting

New wood siding: Make sure to brush the wood clean, working from the top down. Caulk after you stain or prime. If you plan to paint or use a solid-color stain, set any nails that the carpenters missed below the surface and fill the nail holes with caulk.

Weathered wood siding: Stain bonds well to unpainted, weathered wood. If you plan to paint, sand or power-wash the wood to smooth siding that has been exposed to the weather for more than a few weeks. You may have to remove as much as 1/8 inch of the gray, weathered surface to get to the unweathered, natural-colored wood. If you're staining, use a wood restorer or power-wash the wood to bring back its natural color so that staining produces the desired color.

Old painted siding: Scrape off loose paint. Then power-sand to feather the hard edges left by scraping, prime any bare wood, and caulk all joints. Also, set any popped nails, fill the holes with caulk, and spot-prime the siding.

Hardboard siding: You can easily ruin hardboard siding by neglecting maintenance or by doing the work incorrectly. Some of the preparation guidelines include

• Use a 300-degree steam cleaner (a rental item) or scrub the siding with a very hot detergent solution.

• Lightly sand glossy finishes to remove the sheen (called scuff sanding), but sand, scrape, or cut into the surface only as much as is necessary to correct problems. Replace or fill badly damaged areas.

• Don't set nails or you'll break the factory-applied protective coating.

New cedar and redwood: New cedar and redwood bleed tannin. Wash them with a general cleaning detergent and water solution before priming them with a stain-blocking alkyd primer.

Concrete and masonry: Unfinished, fully cured concrete can be finished with concrete stain or paint after being cleaned with a power-washer. Although you can scrape or sand small areas of peeling paint off concrete or masonry surfaces, doing so dulls scrapers and chews up sandpaper quickly. Consider sandblasting or stripping with a chemical remover.

Clean out cracks with a wet-dry vacuum or blow out dust with compressed air before caulking the cracks. Do the same when using a concrete patch, and mist the surface before applying the patch.

Stucco: In many cases, a masonry cleaner is all you need to renew a stucco surface. Hose off the loose dirt and, while the surface is still wet, apply the cleaner to lift the remaining dirt. Then scrub with a stiff brush. If the stucco still looks dingy, consider having a stucco contractor redash the finish.

Power-washing stucco, especially old stucco, is risky. The force of the water can blast the finish off, turning a simple cleaning job into a major repair.

Glossy finishes: Paint doesn't bond well to glossy surfaces. Sanding is a time-consuming and especially difficult on detailed areas of trim, windows, and doors. Brush-on deglosser, available for both oil- and latex-based paints, is an easier way to dull the surface.

Iron railings, siding, and so on: Clean the metal to remove dirt, grime, and oil before priming with a rust-inhibiting primer. Follow the paint manufacturer's cleaning guidelines. Generally, you can use a 50-50 vinegar and water solution for all metal except galvanized steel. Clean new galvanized metal with mineral spirits before priming with special galvanized metal primer.

Rust often occurs under the paint on these surfaces, causing stains and a bumpy finish. Eventually, the corrosion flakes off with the finish. You can eliminate rust by sanding, grinding, or sandblasting. Or, when removing every last spot of rust is impractical, you can use a wire brush to scrape off only the loose, flaking rust and then treat the metal with a chemical to neutralize the corrosion.

Aluminum or vinyl gutters: Avoid painting aluminum and especially vinyl gutters, if at all possible. If you do paint, scuff-sand for better bonding.

Aluminum siding: A good cleaning is generally all aluminum siding needs before you paint.