When acids come into contact with unpainted wood surfaces it speeds up deterioration and can also affect the performance of paint applied to weathered wood. A newly revised FinishLine, Effects of Acid Deposition on Wood, explains why.
In tests conducted near Madison, Wisconsin, smooth-planed wood was allowed to weather before painting. Exposure for as little as two weeks shortened the service life of the subsequently applied paint. The paint bond was weak and the paint eventually peeled. Acid concentration in rain near Madison tends to be much lower than that found in many other areas of the United States. High acid concentration would tend to produce more surface degradation and thus form a weaker paint bond. In any case, wood should be painted as soon as possible after it is installed outdoors.