This SAE Recommended Practice covers a procedure for evaluating plastic and multiple-layer coatings exposed to gravelometer testing (as defined in SAE J400) with an optical imaging and analysis system. The intent of the procedure is to detect, count and characterize instances of damage in the coated surface that fracture the top coat layer or penetrate through multiple layers of the coating system. It may be possible to extend this methodology of coating damage evaluation to specimens that have undergone test procedures or exposures that produce similar, discrete damage sites in the coating system. If so applied, evaluation results must be interpreted with respect to the limitations and intent implied by the original evaluation procedure and its associated rating system, if applicable.
The ISO method is designed only for exterior coatings material. SAE J2661 is a more comprehensive method that covers not only the exterior coatings materials but also exterior plastics, coatings, paints, plastic sheeting materials and so on. The ISO method is not comprehensive in its description of how the evaluation is performed. The SAE method describes details of performance not covered in the ISO method, base on the input of American automakers and their suppliers. The American automakers perform a slightly different type of stone chipping test (Gravelometer Test) compared to the rest of the world due to the road conditions in the U.S. SAE J2661 is technically equivalent to ISO 21227-2.