The most important part of any painting job is proper preparation. I can't even begin to tell you how many people and even contractors paint the outside of a home without even cleaning the exterior off with the proper chemicals to ensure a paint job that lasts.
Preparation of the surface is everything and without it your paint job will fail. Even if the house looks clean I can assure you it is not! Mildew and mold that grows on the paint is sometimes difficult to spot unless you look very closely at the surface. And if you want to see just what I am talking about just mix up about 8 parts of water to one part of household bleach and spray it or sponge it on the surface you are thinking about painting and I can guarantee you will start to see some blackish brown stains start to run down the side of your home.
That's the bleach killing the mildew. And that is what you want to get rid of if you want a paint job that is going to last more than a couple years. Just power washing a house down is not enough.You have to kill the mildew. Yet if you do decide to paint without killing the mildew first , what's going to happen is the fresh new paint over time will become the food for the old mildew and sooner than later your paint job is going to fail. So whoever paints your home; just make sure they get rid of your mold and mildew first or you just wasted a few thousand dollars on a bum paint job! Nuff said.....