Diagnose Common Paint Problems:
Poor Prep and Excess Moisture
Take a good look at your house before you start
painting. You may have to correct some of the wrongs that the previous painter overlooked in desiring to get the job done fast. You may have peeling paint as
shown in Figures A – C.
Poorly prepared surface
You may notice the finished coat of paint peeling away from another coat underneath (Figure A). This is the result of painting over a poorly prepped surface. Usually the surface wasn't cleaned before painting or the primer coat was left too long before the finish coat of paint was applied. You can remedy this situation by firmly scraping
away the paint to get at the surface below. Scrape until you get down to a solid surface that may be part bare wood or a sound, previously painted surface. Sand
and clean the surface thoroughly, let it dry, and prime all bare wood and spot-prime any small bare spots.
Sometimes you find paint and primer falling away from the bare wood surface (Figure B). This is most likely caused by water getting behind the wood or even moisture from the
home’s interior. You can't repaint here unless you stop the source of the moisture migrating through the walls, especially from bathrooms and kitchens. Adding ventilation such as an exhaust fan in the room can frequently help the problem. Many older homes have no vapor barrier, but sometimes applying a vapor barrier paint on the inside will do the trick. If you're stymied, consult a building contractor to help you solve the
problem. Then scrape and sand to remove the loose paint.
Another common problem is cross-grain cracking, sometimes referred to as “alligatoring.” The source of this problem is usually paint buildup from several layers of oil-based paints. Unfortunately, there's no magic bullet for this fix. You'll have to scrape off all the old paint down to bare
wood and then sand the surface. Take precautions and gather this paint onto drop cloths or plastic for disposal because it may contain lead. Don’'t keep applying layers of paint to areas that don't need it such as porch ceilings
and eaves where the surfaces are protected. Often a good cleaning is all they need.
You may find dark mildew spots on the finished coat of paint along shady areas of the house. Buy a special cleaner at paint supply stores to scrub the surface. You can usually stop mildew
by increasing exterior airflow in that area, trimming plants close to the house, and channeling water away with gutters and downspouts. If the area is tough to air out, you can get mildewcide additives for your finish coat
Another problem is chalking, where old paint surfaces get powdery. This is natural for old paints, but you'll have to power wash or scrub the surface and do some light sanding to remove the chalking before applying paint.