ASTM D660-93 pdf free.Standard Test Method for Evaluating Degree of Checking of Exterior Paints.
The illustrated reference standards included in this testmethod are representative of degrees and types of checking ofexterior paint films. These standards are primarily intended forcomparative evaluation.
Definitions of Terms Specific to This Standard:checking,n—that phenomenon manifested in paintfilms by slight breaks in the film that do not penetrate throughthe last applied coating. Where precision is necessary inevaluating a paint film, checking may be described as visible(as seen with the naked eye) or as microscopic (as observedunder a magnification up to ten diameters).
Since checking is not easily recognizable，this testmethod is intended to provide, through definition and illustra-tions,a means of evaluating the degree of this film failure.4.Types of Checking.Many types of checking are recognized, of which someare:Irregular Pattern Type—Checking in which thebreaks develop in the surface of the film in no definite pattern.4.1.2 Line and Short Parallel Type—Checking in which thebreaks in the surface of the film are generally arranged inparallel lines.Switch Type—Checking in which the breaks in thesurface of the film form short and long irregular lines crossingeach other in a wire brushed pattern.Crow Foot Type—Checking in which the breaks in thesurface of the film form in a definite three-pronged pattern withthe breaks running from a center and forming an angle of about120° between the prongs.
Mosaic liype Checking in which the breaks in the surface of the film form straight sided,geometric patternswhich join on all sides.
Shrinkage Type—-Checking in which the breaks in thesurface of the film usually form individual short breaks withshorter irregular breaks progressing at right angles. Short,Random Type——Checking in which breaks inthe surface of the film form short，irregular patterns.Thesebreaks are usually individual and do not join. Sigmoid lype——Checking in which the breaks in thesurface of the film form oval patterns.These oval shapes rarelycomplete their circle.ASTM D660 pdf download.