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Laboratory salt fog tests on E-coated steel often show greater creep from scribed marks when the underlying steel is galvanized than when it is not, while the scab test produces the more realistically greater corrosion on nongalvanized steel. To explain these observations, the corrosion mechanisms, kinetics, and products of both procedures were carefully examined using specimen weight loss, alternating current impedance techniques, and X-ray diffraction analysis. The laboratory tests showed that the salt fog exposure on zinc produced poorly protective oxide and chloride films with linear corrosion kinetics, while the scab test resulted in a more protective carbonate film with parabolic kinetics. Thus, the scab test compares more favorably with natural outdoor exposures of zinc, which generally produce carbonate films. The same tests on steel produced the opposite results, with protective films favored by the salt fog and nonprotective layers by the scab test.