Testing zinc coating adherence is achieved using a stout knife and smoothly running it along the surface of the steel without whittling and gouging, as detailed in the ASTM specifications A123/A123M and A153/A153M. The knife should put a slight mark in the zinc metal surface, but should not cause any flaking or delamination of the layers. Paring or whittling with the knife is not acceptable, and the test should not be performed on corners or edges of the product. Because flaking or peeling of the zinc coating is usually quite obvious and uncommon, the stout knife test, which is a referee test, is rarely performed.
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