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other test methods (pull-off, tape, etc)." Additionally, it states, "Other adhesion test methods may be useful in obtaining quantitative results (See D2197, D3359, D4541, and D7234)." Regardless of the explicit state- ments contained within ASTM D6677, the DOT's consultant refused to accept the results of more than 260 adhesion tests performed by two other consultants in accordance with ASTM D4541. As a result of the DOT's consultant's allega- tion that the coating system would likely fail catastrophically if not removed, the steel fabricator and the general contrac- tor each spent a substantial sum of money on consultants and legal fees. OVERVIEW OF ASTM D4541 & ASTM D6677 There are several ASTM test methods for assessing the adhesion of liquid-applied coatings to a substrate or to a previously applied coating. These test methods are as follows: (1) ASTM D3359, Standard Method for Measuring Adhesion by Tape Test, (2) ASTM D4541, Standard Test Method for Pull Off Strength of Coatings Using Portable Adhesion Testers, and (3) ASTM D6677, Standard Test Method for Evaluating Adhesion by Knife. (Note: ASTM D7234, Standard Test Method for Pull Off Adhesion Strength of Coatings on Concrete Using Portable Pull Off Adhesion Testers, addresses adhesion testing of coatings on a concrete substrate.) This article only discusses ASTM D4541 and ASTM D6677. The reader is advised to obtain a copy of each standard and to follow it when perform- ing testing. ASTM D4541 This quantitative test method involves a procedure for evaluating the pull-off strength of a coating system from metal substrates using portable mechanical, hydraulic, or pneumatic adhesion testers. It maximizes tensi le stress. Fai lure occurs at the weakest plane within the system, which includes the substrate, each coating layer applied, the adhesive, and the test dolly. A test fixture, commonly referred to as a dolly, typically composed of alumi- num, is attached to a properly prepared and cleaned surface using an adhesive compatible with the coating system, and with a rated strength (in psi or MPa) that exceeds the minimum test strength required for the test. After the adhesive cures sufficiently, the adhesion tester is mounted onto the dolly and a mechani- cal, hydraulic, or pneumatic device attempts to remove the dolly from the coated surface. Each component or layer involved in the test is designated according to an alphabetic naming convention detailed in the standard. The substrate is designated as location "A," the first coating layer as "B," the next coating layer as "C," and so on. The adhesive or glue used to affix the dolly to the coated surface is referred to as "Y," and the letter "Z" designates the test fixture or dolly. Three distinct types of failures are possible under ASTM D4541, includ- ing cohesion failure (failure within one distinct layer), adhesion failure (failure between two distinct layers), and glue failure. Under ASTM D4541, a glue failure may occur between the glue and ABOVE ASTM D4541 (Test Method E) showing 100% cohesive failure within the IOZ primer. the test fixture, between the topcoat and the glue, or within the glue itself. A cohesion failure is identified by a single letter, which indicates the layer within which the failure occurred. For example, a 100% cohesive failure within the primer is reported as "B"- 100%. Two letters identifying an adhesion failure, (i.e., B/C), indicate the layers between which the failure occurred. The letter "Y" indicates a glue failure. The three general types of test equipment cited in this standard are based on the means used to perform the pull (i.e., mechanical, hydraulic, or pneumatic). Each piece of equipment is designated within the standard as a Method using the letters B, C, D, E, and F. The Test Method (instrument) used for the test significantly affects the test result values. Tables showing results on four paint systems using di f fer- ent Methods are contained within the standard. The tables accompanying the July 2012 J www.coatingspromag.com 75