Twenty-five years ago, the handyman magazines promised us that someday we'd be able to change the decor of a room as easily as changing clothes—just plug a hose into a wall outlet, press a button for color selection and squeeze the trigger. Today's airless sprayers come pretty close to this description. For large expanses requiring a single color, the labor savings can be truly impressive. Indeed, the speed that spraying offers has changed the painting profession, much as nail guns have in the carpenter's trade. But just as pneumatic nailers don't exempt you from paying attention to basic structural requirements, neither does spraying magically allow you to ignore fundamental painting principles. I spray a lot, but the decision is by