A thorough scrubbing is a must before painting any exterior surface. It removes the dirt and broken-down paint residues that keep fresh coats from adhering and gets rid of mildew that grows on paint in all but the most arid climates. Most contractors clean with pressure washers, but in the hands of someone unfamiliar with the equipment, these can gouge wood, shatter glass, and drive water behind siding and trim. Using a hose, a pump sprayer, and a scrub brush is slower but safer, and just as effective.
to be the devils advocate i have been a building contractor 20 of the last 30 yrs. i do know that if you go to a higher sheen of paint and or darker colors then any imperfections in the walls will show up much more dramatically…therefore the painter or a good drywall finisher is needed to prepare the walls extensively. this could cause more expenses…for it takes a lot of time to prep walls (smooth walls..not textured walls) and this cost has to be absorbed. House Painting Wheat Ridge, CO