Welcome to our continuing series on paint finishes.  If there are any questions that you may have drop us a note and we will try our best to answer your questions.

PEELING, CRACKING AND BLISTERING PROBLEMS

The peeling of paint and other film-forming finishes is often caused by the wood becoming wet and staying wet for long periods of time. Exterior wood must be protected from excess wetting. Brittle paints are more likely to have peeling problems than are the more flexible paints like those based on acrylic latex resins.

INTERCOAT PEELING

Intercoat peeling is the separation of the new paint coat from the old, which indicates that the bond between the two coats is weak. Intercoat peeling usually results from inadequate cleaning of the weathered surface prior to repainting and generally occurs within one year of repainting. This type of paint peeling can be prevented by good cleaning and painting practices. Intercoat peeling can also occur on freshly painted wood if too much time elapses between application of the primer coat and topcoat. If more than two weeks elapse before a topcoat is applied to an oilbased primer, soaplike materials may form on the surface and interfere with the bonding of the topcoat.

CROSS-GRAIN CRACKING

Cross-grain cracking occurs when paint coatings become too thick. This problem often occurs on older homes that have been painted several times. Normally, paint cracks in the direction it was brushed onto the wood (that is, with the grain). Cross-grain cracks run across the grain of the wood and paint. Once cracking has occurred, the only solution is to completely remove the old paint and apply a new finishing system on the bare wood.

To prevent cross-grain cracking, follow the paint manufacturer’s recommendations for spreading rates. Do not repaint unweathered, protected areas such as porch ceilings and roof overhangs as often as the rest of the house. If possible, repaint these areas only as they weather and require new paint. If repainting is required, clean the areas with a sponge or bristle brush and detergent in water to remove any water-soluble materials that will interfere with adhesion of the new paint. Latex paints, based on either vinyl-acrylic or acrylic polymers, have not been known to fail by cross-grain cracking.

BLISTERING

The blistering of paint is not as common as it was when lead-based paints and oil-based paints were in more use. Temperature blisters are bubble-like swellings that occur on the surface of the paint film as early as a few hours or as long as one to two days after painting. They occur only in the last coat of paint. The blisters are formed when a thin, dry skin forms on the outer surface of the fresh paint and the liquid thinner in the wet paint under the skin changes to vapor and cannot escape. When the direct rays of the sun fall on freshly painted wood, the rapid rise in temperature causes the vapors to expand and produce blisters. Usually, only oil-based paint blisters are formed in this way. Dark colors that absorb heat and thick paint coats are more likely to blister than are white paints or thin coats. To prevent temperature blisters, avoid painting surfaces that will soon be subject to the heat of the sun.

OTHER FAILURE PROBLEMS

Other failure problems that can occur on finished wood surfaces include such things as blue staining, water staining, varnish deterioration and discoloration, erosion of semitransparent stains, and discoloration of transparent finishes. These additional failure problems are discussed in more detail in the publications listed in the additional reading section.