Peeling - This usually occurs on protected surfaces such as overhangs and porch ceilings. Chemical salts that were not washed off the old surface before it was repainted are usually the cause of peeling, or it may be the result of painting over a glossy surface.
Solution: The old paint must be scraped off and the surface needs to be thoroughly sanded. Then wash the surface with a phosphate-based detergent (TSP). Rinse thoroughly then let it dry. A primer may be necessary - this depends on the type of paint you select - check the label.
Mildew ? This is a fungus growth caused by high humidity and temperature. If it is not gotten rid of before you paint, it will grow through the new paint.
Solution: Mix a solution of one part bleach and four parts water. Scrub the surface thoroughly to remove all mildew. Be sure to wear rubber gloves to protect your hands. Hose the surface down thoroughly. Let dry.
Blistering - is usually a two-fold problem caused by moisture trapped in the siding which pushes the paint away from the surface. It may be a sign that there is a leak in the roof, eaves or the plumbing. Lack of ventilation in the kitchen and/or bathrooms could also be a cause.
Solution: First you?re going to need to find the source of the moisture and correct the problem. Then scrape the blistered area down to stable paint or wood. Sand the surface. A primer may be necessary before you paint - this depends on the paint you select - check the label.
Flaking ? This usually occurs after peeling or blistering, with the paint breaking completely away from the siding.
Solution: Follow the same steps given for Blistering.
Alligator Cracking - If the siding is plywood or masonry, the problem may be caused by cracks in the siding. If it?s not, it indicates that the top coat of paint has shrunk and pulled away from the undercoat. This condition usually occurs only on very old painted surfaces.

Solution: Scrape or sand the surface until you reach stable paint or wood. Hose it down well. A primer may be necessary before you paint - this depends on the paint you select - check the label.
Wood Rings or Staining ? This is due to rust from (a) nailheads or (b) sap bleeding from a knot hole.
Solution: (a) Remove rust from nailheads by sanding. Countersink nailheads and prime with a metal primer. Cover with wood putty and sand. (b) Prime knot holes and sap streaks with a shellac based primer. In either case, once the area has been primed, cover it with two coats of paint.