P. O. Box 815
TECHNICAL MEMO # 16 : Methods of rating test specimens.
NUMERICAL RATINGS are applicable to a wide variety of tests. However, when used alone they are not considered descriptive enough for the failures encountered in some types of tests. Values of 0 to 10 are used, with a rating of "0" indicating total failure, and a "10" rating indicating no failure.
BLISTERING is commonly encountered as a result of salt spray testing or a variety of humidity, boil, or soak tests. It is rated numerically as above in accordance with the photographic reference standards in ASTM D714-56, Methods for Evaluating Degree of Blistering of Paints. Where possible, the numerical rating is enhanced by the addition of several codes: "B" for general blistering due to system failure, "C" for blister patterns which suggest concentrations of rinse solution salts, "D" for blisters which have the pattern characteristic of drips falling on the work, and "G" for blister patterns which appear to be due to glove or fingerprints, or other handling marks.
CORROSION CREEPAGE is primarily used in rating salt spray performance, and will be reported as creepage from the scribe line in 1/16 inch increments in accordance with ASTM D1654-79a, Method of Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments. The rating may be enhanced by the use of "S" as a code to indicate an isolated spot failure that is not representative of the test in general. This spot may be the only failure, or significantly in excess of the average creepage.
FIELD CORROSION (corrosion unrelated to the scribe line) will be rated according to the photographic references in A. S. T. M. D610-68, Method of Evaluating Degree of Resistance to Rusting with Paint on Iron or Steel Surfaces, or as a percentage of the surface if necessary.
OTHER DESCRIPTIVE CODES may be used to further describe the type or intensity of corrosion: "R" or "W" to indicate red or white rust, "VL", "L", "M", "H", or "S" to indicate very light, light, moderate, heavy, or scab corrosion.
ADHESION is an indication of the bond between the finish and the surface, and is rated numerically as follows: 10 - adhesion equal to paint film integrity (paint film will shear without loss of adhesion), 8 - no loss of adhesion in crosshatch adhesion test, 6 - no complete squares lost in crosshatch adhesion test, 4 - complete squares lost in crosshatch adhesion test, 2 - paint will pick off in spots with a Scotch Tape pull, 0 - a Scotch Tape pull will remove the paint.
FILM THICKNESS is measured by an appropriate means and reported in mills.
HARDNESS is tested using a standard pencil hardness test, and reported as the hardest lead that will not cut the film.
FLEXIBILITY will be measured by ASTM D522-60 Conical Mandrel or ASTM D2794-69 Impact test. Any resulting peeling will be reported in 1/16 inch increments from the small end of the conical mandrel, or from the center of the convex side of the impact dimple, and is defined as paint removed by a Scotch Tape pull . "F" is used as a code to indicate that the paint film cracked or fractured, but without any significant film loss to the subsequent Scotch Tape pull.