Peeling paint can have a number of causes but all of them are aggravating! Most often, the reasons are water-related and include water leaks, painting in very humid weather and applying a second coat of paint when the first has not had time to dry. The other frequent cause of peeling paint on walls is application of one kind of paint over another kind.
Scrape off peeling paint and feel for moisture underneath. Even if your wall does not feel wet, run your hand over surrounding areas. Areas of plaster or other interior surfaces troubled by moisture often feel cooler than areas where paint is sound. You may also see cracks or dimples in plaster affected by moisture. Defer repainting until you can find the possible moisture source.
Examine the full range of possible moisture sources. In an apartment, look for plumbing drips or high sources of moisture (like poor ventilation if bathroom walls are peeling). Find out or ask for your superintendent's help in determining whether the problem may stem from your next door neighbour's apartment or the one above you. Peeling paint on an outer wall or one containing a window may be caused by problems in the window-frame, a minor roof leak or even the pointing (mortar) of an exterior wall. You may have to wait until your landlord can tackle the problem.
Add to your list of possible moisture sources you to check if you live in a private house. Cracks in exterior stucco, paint or siding may cause peeling on inside walls. Check roof surfaces, gutters and chimney flashing (even if your chimney's on one side of the house, water travels along beams to cause moisture problems in other areas). Check both from the outside and from the attic, if possible. Look hard at overgrown plantings; poor air circulation caused by big bushy shrubs may be the source of peeling paint on inside or outside walls.
Fix the suspected cause first, then repaint. Scrape and sand off all peeling paint and any paint on the edges loosened while scraping. Repair cracks or dimples in plaster with spackle. Several thin coats are more effective than a single thick one. Sand spackled area when dry so that area blends smoothly into the rest of the wall.
Apply water-resistant primer in a thin coat and let dry thoroughly. Apply wall paint, using nearly-dry brush to feather edges of the newly painted patch, blending them into existing paint. In case of large peeling areas, you may have to paint the whole wall.
Determine, especially if peeling is widespread, whether your peeling wall was last painted during very humid weather. This can be true on both exterior and interior walls. High humidity can interpose a barely detectable layer of moisture on a wall, making it hard for new paint to adhere. Eventually, as humidity lowers, you will see bubbling, peeling or flaking. Scrape and sand to produce an even surface and repaint when you can be certain of at least a copy of dry breezy days.
Find out how quickly your peeling wall was last painted. A rush job, which involves adding a new paint coat the moment the previous coat seems dry or nearly so, looks fine when it's first completed. Paint, however, dries from the outside in, and paint that feels just barely dry on the surface can still be wet underneath. Blocking the air circulation each coat needs to dry can produce eventual peeling. Scrape, sand and allow at least 24 hours for each coat of paint to dry. Oil-based paint can do with 48 hours per coat.
Make sure, before you paint, that you have chosen the right kind of paint for your new job. Covering old oil-based paint with new latex, or the other way around, or layering on one of the new alkyds, coloured stains, or glazes is often a recipe that ends with peeling. If your previous paint job is very old or you cannot determine what kind of paint was used earlier, plan to begin your job with a primer coat to insure good adherence.
Don't get discouraged if your first solution is only partial. Peeling problems can be tricky, persistent, and in need of more than one strategy--professional painters will agree. Be proud of the progress you make and keep trying.