Adhesion Testing of Epoxy Coating

The hot water and knife adhesion tests developed in this study proved to be a valuable tool for quality control and for in-depth studies of coating adhesion. Hot water and knife adhesion tests were very useful in discriminating and identifying good from bad quality coatings. The tests were relatively easy to perform and did not require special or sophistocated equipment. Most of the subjectivity involved in other adhesion tests was eliminated or reduced through the use of a calibrated knife. Nevertheless, it was shown that the subjectivity of the tests had little or not effect in the detection of coatings with poor adhesion. Test parameters such as knife force calibration procedures, adhesion test method, test operator, type of knife and blade, and test evaluator had little effect on the test results. Sample source was the most influential factor in determining adhesion strength. The quality of coating application by different coaters can vary greatly and affects adhesion of the coating. An interesting finding was the good agreement observed between results from hot water-adhesion tests and those from the TxDOT peel test. Considering that the TxDOT peel test is simple and quick to perform, the test is useful for adhesion evaluation, especially if a calibrated knife is not available. Another important finding was the poor correlation observed between knife adhesion tests and bend tests. Bend tests were not reliable indicators of coating adhesion and were more a measure of the coating flexibility. Therefore, the use of bend tests as the only method of testing epoxy coating adhesion (as proposed in some ECR standards) is discouraged.