Remember when we told you that it's critically important to paint on a moisture-free surface? Forget that for a second. Once you've stripped off old paint and patched up busted siding, you need to attack another unsightly plague of old houses: mold and mildew. And the best way to do that is with an old-fashioned scrub and rinse.
Mold, mildew and other fungi can embed themselves deep in wood fibers far beyond the reach of a scraper or sander. The best weapon is to mix up a diluted solution of 1 cup (236 milliliters) each of bleach and trisodium phosphate to 2 gallons (7.5 liters) of water [source: Lernley]. Use a spray bottle to spritz problem areas and scrub deeply with a stiff-bristled brush.
Let the bleach solution do its work for a few hours before giving the entire house a gentle rinse to remove dust and paint debris. It's tempting to use a power washer, but that convenience can come at a price — high-powered streams of water can gouge softer woods. When in doubt, try a regular garden hose [source: Hurst-Wajszczuk].
OK, now you can remember our moisture advice. Wait a few sunny days after rinsing before proceeding with the painting project.