When painting a home with a wood exterior , it’s not unusual to find areas that are worn and weathered. In extreme cases, the entire house may be weather-beaten.
Sometimes, a home is this way because it’s been years since the last paint job. But even new construction – a recent addition, for example – can be “weathered” after only a few weeks if unpainted wood is left exposed to the elements.
“If the wood exterior you’re about to paint meets one of these descriptions, you’ll need to do some extra surface preparation ,” says Debbie Zimmer, spokesperson for the Paint Quality Institute. “That’s the only way to end up with a high quality, long-lasting paint job on weathered wood.”
Assuming that the wood has been painted before, start your surface preparation by scraping away all of the loose or peeling paint. (But if your home was built before 1978 and you suspect the presence of lead-based paint, first call 1-800-424-LEAD to learn how to avoid potential health hazards.) Then, carefully inspect the exterior of your home for damaged or rotted wood.
Dry rot (dry, crumbly sections of wood) and wet rot (soggy, soft spots) are both caused by microorganisms that thrive in damp conditions. Rot can destroy the wood  so completely that a finger can be pushed right through it. To test for rot, poke suspicious-looking boards with a screwdriver; if it goes in easily, the wood has rotted.
Remove all of the rot you find. Use wood filler to repair small problem areas, and totally replace any wood that is damaged beyond repair. If the damaged wood is structural – roof support posts, railing posts on elevated decks, and the like – consider hiring a professional to make the repairs.
Since wood can rot wherever there is excess moisture, be sure to caulk and seal inside and outside corners, seams, and other gaps in the wood exterior where rain or other moisture could penetrate the surface. For the best performance, use a paintable siliconized acrylic caulk.
Thoroughly sand surfaces that have any degraded wood fiber. If you are painting cedar shakes or another type of wood that is uneven, use a wire brush rather than sandpaper for this work. Then brush off the surface.
Next, wash off any remaining dust with a power washer, or scrub the surface with soapy water using a long-handled brush. Start at the top of the wall and work down toward the bottom. Be sure to rinse off the soap residue.
If any mildew remains, remove it by applying a solution of one part bleach to three parts water, letting it sit on the surface for 20 minutes, then scrubbing it away. Again, rinse the area clean.
Apply a coat of top quality latex or oil-based primer to the entire exterior. Then finish the project by applying one or two coats of top quality 100% acrylic latex exterior paint . (A second coat will provide better protection from the elements and make your new paint job last longer.)
“When painting weathered wood, you may be tempted to skip the extra work required to properly prepare the surface, but it’s a temptation you have to resist,” says Zimmer. “By going about the project in the right way, you’ll be rewarded with many years of great performance from your new paint job.”