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[BoltBuddy92]

In an automotive subframe project using M12 class 10.9 bolts, exposed to salt spray and vibration, I’m looking into zinc flake coatings for corrosion protection. Curious if doubling the coating thickness—from 8 µm to 16 µm—actually improves durability in the field, or if benefits plateau and sealing topcoats make a bigger difference. Has anyone seen clear data or long-term results on this?

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[Thomas Fischer]

We did comparative testing on a commercial van platform—8 µm vs 15 µm zinc flake, both with the same topcoat. In salt spray and vibration scenarios, there was only about a 10–15% improvement in red rust resistance with the thicker coat. However, most of that came from the consistency of the topcoat. Also, 16 µm caused thread tolerance issues on some of our Class 3 fitments. I’d say focus more on topcoat quality and application control.

If you are curious, we used an inorganic, water-based clear topcoat. Excellent torque control and good resistance to chipping during installation. Honestly, if your topcoat is solid, I wouldn’t bother going past 8 µm—just make sure the application is consistent.

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[neil barnes]

+1 to what you said. We ran field trials over two harsh Ontario winters—lots of salt, moisture, and vibration. Bolts with 8 µm zinc flake and a well-applied topcoat showed no significant corrosion difference compared to the 16 µm ones. In fact, some 16 µm samples had torque issues. Save the budget—focus on consistent topcoat application and proper curing.

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