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A paint film is a dynamic entity. During its life it is in a slow but continuous state of change. Good weathering requires an unusual balance or compromise of physical and chemical forces within the paint film as it ages. There are perhaps some thirty types of physical and chemical actions within a paint film that cause it to change as it weathers. Many of these forces have been measured, and the rate of change of these forces in the aging film appears to dictate the useful life of the film. The importance of such factors as relative humidity, uniformity of film, film thickness, film shrinkage, moisture sorption, amount of film applied, and physical structure and a rating system for summarizing film properties are discussed in this paper. The field of weathering is so broad that only two general types of films weathered under atmospheric conditions will be considered in this paper: white type house paints and metal protective paints. House paints are primarily linseed oil base paints and metal protective paints are primarily oleoresinous base paints. The weathering of paints is big business. At our test fences and marinebasin at Sayville, L. L., there probably are 25,000 tests under way this year even though only 400 or 500 tests are added each year. There are two andone-half miles of test panels. ASTM Committee D-1 is considering weathering test sites because of the importance of having adequate weathering data.
Dunn, E. J.
National Lead Co., Brooklyn, N. Y.