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NEVER AGAIN ADHESION TEST METHODS – MAKING SURE THE RESULTS STICK BY MIKE O'BRIEN A dhesion testing is commonly used during coating failure investigations; however, sometimes the wrong type of adhesion test is performed, the results are misinterpreted, or the procedures and reporting requirements in the test methods are disregarded. This article addresses some common issues related to ASTM D4541 and ASTM D6677 adhesion testing and provides readers with a proper understanding of differences between these two test methods. DIFFERENT ADHESION TESTS – DIFFERENT RESULTS Several years ago, a consultant, working for a large inspection firm in the United States, convinced state Department of Transportat ion (DOT) person- nel that the adhesion of an inorganic zinc (IOZ) primer was inadequate on a large bridge with over 400,000 square feet (37,161.22m2 ) of steel. The consul- tant recommended that all coatings be removed and replaced on this the bridge. This recommendation was based primarily on qualitative and subjective testing he conducted on portions of the bridge, reportedly in accordance with ASTM D6677. According to the consultant's report, greater than 61% of ASTM D6677 adhesion tests conducted on the exterior, and 65% of the tests on the interior box girders displayed poor cohesion strength The purpose of the procedures within a standard is to ensure that different individuals perform the test following the same procedures and that they report the results using the same criteria. 74 CoatingsPro J July 2012 ABOVE ASTM D4541 (Test Method E) showing 65% cohesive failure in IOZ primer, 20% glue failure, and 15% cohesive failure in red topcoat. of the inorganic zinc. However, the consultant did not follow the procedures contained within ASTM D6677 and even developed his own rating system, disre- garding the rating system contained within the standard. Two other consultants, one hired by the general contractor and the other hired by the fabricator, performed adhesion tests using ASTM D4541, (a quant itative adhesion test method), and their results provided a completely different picture regarding the adhesion of the coating system. ASTM D4541 testing indicated that approximately 96% of the areas tested displayed satis- factory adhesion. Why such different results? These two test methods differ significantly in several ways. One test is quantitative, and the other is qualitative and subjec- tive. ASTM D6677 states that the test method is subjective and qualitative and "does not have any known correlation to