You scuff up existing paint for two reasons. First, you want to get rid of any oil, grease or dirt trapped in the top layer of paint. This is the stuff that cleaners and degreasers can't get off. The second reason to scuff is to set up a physical bond for the new primer and paint to adhere to. You want to give the old paint some tooth so the new sticks better. Paint should not be applied to a concrete basement floor until the concrete has aged for at least a year. The floor should be dry when painted, the best time for application being during the winter or early spring (assuming there is some heating apparatus in the basement), when the humidity in the basement is low. In general, three coats of paint are required on an unpainted floor, and the first coat should be thin to secure good penetration. After the paint is dry, it should be protected with a coat of floor wax. The paints may be applied by brush or spray; the small spray attachment for vacuum cleaners is very convenient, especially for painting radiators.
Water-thinned rubber-latex paint is already an old reliable, though it is only about 10 years old. It accounts for a big percentage of all paint sold and is still the most widely available of the easy-to-use finishes. One new type is a combination vinyl-rubber paint that is said to do a better job on interiors than either vinyl or rubber alone because it dries faster, lasts longer and has less sheen. Airless Tip: If you have somebody who can start masking off the trim, have them start on that while you convert the airless to a new color. When changing colors with an airless paint sprayer it is a good idea to have a second bucket filled half way with clean water. Place the intake hose in the clean water gently without getting the old color everywhere in the water. Take the tip out of the airless and spray all of the old paint out of the hose and back into its original paint bucket. Be careful when doing this that you recognize when the paint starts turning watery. When it does point the gun into the first bucket and spray until it looks pretty clean. It doesn't need to be perfectly clean. When it looks good, clean off the intake line in the clean bucket and get the old color off the intake line. Now place the intake line inside of your new trim paint. Following a European directive, the British paint industry has reduced VOCs in two stages, the second of which came into force in January last year. Now that you have primed the airless, make sure that there isn't a tip in the gun of the airless and bring it over to the empty bucket. Since there is typically cleaning solution in the hose leading to the gun it is a good idea to spray that out until you see thick paint coming out. Once you have thick paint coming out you may put your tip back in. Remember that the tip will have an arrow on one side of the handle that shows which direction it must be in, in order to spray.