Poor surface preparation is where most paint failures occur. Any time you paint over a glossy, slick, dirty, greasy surface that is not properly prepared, you are asking for paint problems.
Liquid sand paper removes grease, dirt, and dulls the finish so the paint will adhere to the wall surface. It is easy to use. All you have to do is dampen a cloth with the liquid and wipe the wall surface.
Other surfaces that have potential paint problems are cement, paint with mildew growth, vinyl, peeling paint, new sheetrock, and new wood. Cement contains alkaline, which causes hot spots and burns on the painted surface. This problem is eliminated by washing off the alkaline with one of the many compounds available for that purpose before painting.
Some people think they can cover mildew by just painting. The problem is the mildew has to be removed before painting or the mildew continues to grow and works up through the new paint. Trying to paint over vinyl presents some painting problems. Vinyl paneling or vinyl wall covering cannot be painted unless the vinyl has been prepared with a special material, which makes it so the paint bonds to the vinyl surface. A flat finished wall can also present a painting problem. If you paint a flat finish onto another flat finish, the paint may appear shinier in some areas. You may need to prime the wall surface and then use a paint with a flat finish. Peeling paint may mean moisture is under the paint. If there is a moisture problem, determine where the moisture is coming from and eliminate the moisture before repainting.
To paint new sheetrock, the first coat should be a latex primer, not an oil-based primer. The latex primer lays the sheetrock nap down, resulting in a smooth finish coat. On new wood, use an oil-based primer. This is because the water in the latex causes the wood to swell, therefore, requiring more sanding.