Sanding not only feathers out chipped paint but also provides "tooth" for the next coat of paint. For glossy trim, use a sanding sponge rather than sandpaper. Sponges mold to the shape of the trim and last longer than paper. When applying latex over alkyd paint or when he is not sure of the original finish, Brian Doherty, a painter in Richmond, Virginia, follows the hand-sanding with liquid sandpaper to make sure the surface is completely deglossed to prevent incompatibility problems. "I've seen homes where latex was used on oil-painted trim, and the paint started to peel in less than a year," says Doherty.
Oh, where to begin? Let me start with 'watered down paint'. 25-50% before the material gets to the site? Impossible. You would basically be painting with water at that point. It would be less of a hassle, and cost, to simply use proper material. You would be forced to apply three coats instead of two, as the coverage would be horrible. Whatever cost you think might be saved in materials would be lost in labor.
Even if you think you'll probably do the job yourself, it's good preparation to seek estimates from professional home painters, whether your painting the exterior or interior of your home. Then you'll have a financial point of comparison and you may benefit from what a home painting contractor has to say about the condition of your home, color choices and types of paint available. Let the painter make his pitch for a professional job before you decide what to do. You can still opt to do it yourself while having learned something worthwhile.
We were performing some remodeling in conjunction with the painting project and Henry's crew was able to work with and around our contractor with ease. Henry's crew was ahead of schedule, so they were able to start our project early (nearly a week ahead of schedule) and ended up finishing the project the day they were originally scheduled to start!
This painter Scot never came and finished the job. Texted me at 6:30 in the morning saying that he isn't able to do the job I gave him. I would not recommend this painter to anyone. I will make sure everyone I know won't use this guy. He is the worse business owner I have ever met. I don't know how he is in business. Be very careful of this guy Scot. Don't trust him and don't pay him for anything for any work.